P2C(1) (local) P2C(1)
NAME
p2c - Pascal to C translator, version 1.19
SYNOPSIS
p2c [ options ] [ file [ module ] ]
DESCRIPTION
P2c is a tool for translating Pascal programs into C. The
input consists of a set of source files in any of the
following Pascal dialects: HP Pascal, Turbo/UCSD Pascal, DEC
VAX Pascal, Oregon Software Pascal/2, Macintosh Programmer's
Workshop Pascal, Sun/Berkeley Pascal. Modula-2 syntax is
also supported. Output is a set of .c and .h files that
comprise an equivalent program in any of several dialects of
C. Output code may be kept machine- and dialect-
independent, or it may be targeted to a specific machine and
compiler. Most reasonable Pascal programs are converted
into fully functional C which will compile and run with no
further modifications, although p2c sometimes chooses to
generate readable code at the expense of absolute
generality. P2c endeavors to insert notes and warning
messages into the output code to point out areas which may
require human intervention. Output code is arranged to be
readable and efficient, and to make use of C idioms wherever
possible. The main goal of the translation is to produce C
files which are pleasant and "natural" enough to be
acceptable as the new source files for a program. In a
pinch, p2c will also serve as an ad hoc Pascal compiler.
Code generated by p2c normally does not assume characters
are signed or unsigned. Also, it assumes int is the same as
either short or long but does not depend on which. However,
if int is not the same as long it is best to use a modern C
compiler which supports prototypes. Generated code does not
require an ANSI-compatible compiler (unless ANSI-style code
is requested), but it does use various ANSI-standard library
routines.
All generated code includes the file <p2c/p2c.h> which in
turn includes <stdio.h> and various other common resources.
Also, many translated programs will need to be linked with
the run-time library, typically -lp2c.
Given a file name, p2c reads from the specified file and
outputs to a file with a .c suffix added or substituted.
For example,
p2c myfile.pas
reads from myfile.pas to produce the file myfile.c. The
input file may contain a Pascal main program or a single
Pascal module (or "unit" in Turbo and UCSD Pascal
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nomenclature), or it may just contain a number of procedures
and declarations. P2c is designed to work for correct input
programs. That is, it will accept partial programs but may
occasionally core dump if the input refers to undefined
symbols.
If the input is a module, the translator will also produce a
file module.h containing a translation of the module's
interface section. The implementation section may be
omitted in which case only the .h file will be interesting.
If the program or module has include files, these may cause
additional .c files to be generated depending on the value
of the ExpandIncludes option (see below).
If no file name is given, p2c reads Pascal from the standard
input and writes the resulting C to standard output (though
a .h file may still be produced). If a file name and module
name are given, the file may include several modules (or
units). The specified module is translated; any others are
skipped. The output files will be named module.c and
module.h. P2c never translates more than one module per
run.
Before starting, p2c reads the file /usr/lib/p2c/p2crc for a
number of configuration parameters. (The actual path used
on your system may vary. The -i option is a handy way to
examine this file.) If the P2CRC environment variable is
set, it gives the name of a file to read instead of the
system file; this file can start with Include %H/p2crc to
include the system file. Next, p2c attempts to read the
file p2crc in your directory for further configuration. If
this file does not exist, p2c looks for .p2crc instead.
OPTIONS
-o cfile
Use cfile in place of file.c or module.c as the primary
output file. A single dash (`-o -') says to write the
C code to the standard output.
-h hfile
Use hfile in place of module.h as the output file for
interface text. This only has effect if the input is
an HP Pascal module or a Turbo Pascal unit.
-s sfile
Read interface text from sfile before beginning the
translation. This file typically contains one or more
modules, often with interface sections omitted for
speed, which the program or module being translated
will use. (Typically the ImportFrom and ImportDir
parameters in p2crc are set up to allow p2c to locate
interface text without needing any -s options.) If
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there are several -s options in the command, the sfiles
are read from left to right.
-pn Display progress of translation in the form of a line
number/file name display. This is refreshed every n
lines, 25 by default.
-c rcfile
Read local configuration commands from rcfile instead
of p2crc or .p2crc. A dash (`-c -') in place of rcfile
causes no local configuration file to be used.
-v ("Vanilla.") Do not read from the system configuration
file /usr/lib/p2c/p2crc. Since some of the parameters
in this file are required, your local configuration
file must include those parameters instead. This also
suppresses the file named by the P2CRC environment
variable.
-H homedir
Use homedir instead of /usr/lib/p2c as the p2c home
directory. The system p2crc file will be searched for
in this directory.
-Ipattern
Add pattern to the ImportDir search list of places to
find modules which are imported. The pattern should
include a %s to represent the module name, and should
evaluate to a potential file name for that module's
source code. For example, ../%s.pas looks for
modulename.pas in the parent of the current directory.
-i This special option (which must be the only argument on
the command line if used) simply copies the system
configuration file /usr/lib/p2c/p2crc to the standard
output in its entirety. (It may be used with -H, but
-i is most useful precisely when you don't know the
location of the home directory.)
-q Quiet mode. Suppresses output of status messages
during translation.
-En Abort translation after n errors. If n is omitted it
defaults to zero, which means unlimited errors are
allowed. Use -E1 to make p2c halt after the first
error.
-e Echo the Pascal source into the output file, surrounded
by #ifdefs. This is the same as the CopySource
parameter in the p2crc file.
-a Produce modern ANSI C. This is a convenient override
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for the AnsiC parameter in the p2crc file.
-L language
Select input language name, such as VAX or TURBO. This
is a convenient override for the Language parameter.
-V Verbose mode. This causes p2c to generate an
additional ".log" file with further details of the
translation, such as a list of warnings and notes
including those which are suppressed in the regular
output.
-M0 Disable memory conservation. This prevents p2c from
freeing various data structures after translating each
function, in case this new conservation feature causes
unforseen problems.
-R Regression testing mode. Formats notes and warning
messages in a way that makes it easier to run diff(1)
on the output of p2c.
P2c also understands a few debugging options which may
occasionally be useful when tracking down translation
problems. The -dn option sets the "debug level" to n, a
small integer which is normally zero. Debugging output is
written into the regular output file along with the C code;
the higher your n, the more "wallpaper" you get. Also, -t
prints debugging information at every Pascal token, -Bn
enables line-breaker debugging, and -Cn enables comment
placement debugging.
CHOICE OF SOURCE LANGUAGE
The Language configuration parameter or -L command-line
option tells p2c which Pascal dialect to expect in the input
file. Any language features which do not overlap between
dialects are supported all of the time. The Language
parameter is consulted when a syntax or usage is detected
that has different meanings in two different dialects, and
also to determine default values for various other
translation parameters as described below.
The following language words are supported by p2c. Names are
case-insensitive.
HP HP Pascal. This is the default language. All
features of HP Standard Pascal, the Pascal
Workstation version, are supported except as noted
in BUGS below. Some features of MODCAL, HP's
extended Pascal, are also supported. This is a
superset of ISO standard Pascal, including
conformant arrays and procedural parameters.
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HP-UX HP Pascal, HP-UX version. Almost identical to the
"HP" dialect.
Turbo Turbo Pascal 5.0 for the IBM PC. Few conflicts with
HP Pascal, so the Language parameter is not often
needed for Turbo. (Most important is that the Turbo
and HP dialects use 16 and 32 bit integers,
respectively.)
UCSD UCSD Pascal. Similar to Turbo in many ways.
MPW Macintosh Programmer's Workshop Pascal 2.0. Should
also do a pretty good job for Lightspeed Pascal.
Object Pascal features are not supported, nor is the
fact that char variables are sometimes stored in 16
bits.
VAX VAX/VMS Pascal version 3.5. Most but not all
language features supported. This has not yet been
tested on large programs.
Oregon Oregon Software Pascal/2. All features implemented.
Berk Berkeley Pascal with Sun extensions.
Modula Modula-2. Based on Wirth's Programming in Modula-2,
3rd edition. Proper setting of the Language
parameter is not optional. Translation will be
incomplete in most cases, but should be good enough
to work with. Structure of local sub-modules is
essentially ignored; like-named identifiers may be
confused. Type WORD is translated as an integer,
but type ADDRESS is translated as char * or void *;
this may cause inconsistencies in the output code.
Modula-2 modules have two parts in separate files.
Suppose these are called foo.def (definition part)
and foo.mod (implementation part) for module foo.
Then a pattern like %s.def must be included in the
ImportDir list, and LibraryFile must be changed to
refer to system.m2 instead of system.imp. To
translate the definition part, give the command
p2c foo.def
to translate the definition part into files foo.h
and foo.c; the latter will usually be empty. The
command
p2c -s foo.def foo.mod
will translate the implementation part into file
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foo.c.
Even if all language features are supported for a dialect,
some predefined functions may be omitted. In these cases,
the function call will be translated literally into C with a
warning. Some hand modification may be required.
CONFIGURATION PARAMETERS
P2c is highly configurable. The defaults are suitable for
most applications, but customizing these parameters will
help you get the best possible translation. Since the
output of p2c is intended to be used as human-maintainable
source code, there are many parameters for describing the
coding style and conventions you prefer. Others give hints
about your program that help p2c to generate more correct,
efficient, or readable code.
The p2crc files contain a list of parameters, one per line.
The system configuration file, which may be viewed using the
-i option to p2c, serves as an example of the proper format.
Parameter names are case-insensitive. If a parameter name
occurs exactly once in the system p2crc, this indicates that
it must have a unique value and the last value given to it
by the configuration files is used. Other parameters are
written several times in a row; these are lists to which
each configuration line adds an entry.
Many p2crc options take a numeric value of 0 or 1, roughly
corresponding to "no" or "yes." Sometimes a blank value or
the value "def" corresponds to an intermediate "maybe"
state. For example, the stylistic option ExtraParens
switches between copious or minimal parentheses in
expressions, with the default being a nice compromise
intended to be best for readers with an average knowledge of
C operator precedences.
Configuration options may also be embedded in the source
file in the form of Pascal comments:
{ShortOpt=0} {AvoidName=fred}
{FuncMacro slope(x,y)=atan2(y,x)*RadDeg}
disables automatic short-circuiting of and and or
expressions, adds "fred" to the list of names to avoid using
in generated C code, and defines a special translation for
the Pascal program's slope function using the standard C
atan2 function and a constant RadDeg presumably defined in
the program. Whitespace is generally not allowed in
embedded parameters. The `=' sign is required for embedded
parameters, though it is optional in p2crc files. Comments
within embedded parameters are delimited by `##'. Numeric
parameters may replace `=' with `+' or `-' to increase or
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decrease the parameter; list-based parameters may use `-' to
remove a name from a list rather than adding it. Also, the
parameter name by itself in comment braces means to restore
the parameter's value that was current before the last
change:
{VarFiles=0 ## Pass FILE *'s params by value even if
VAR}
some declarations
{VarFiles ## Back to original FILE * passing}
causes the parameter VarFiles to have the value 0 for those
few declarations, without affecting the parameter's value
elsewhere in the file.
If an embedded parameter appears in an include file or in
interface text for a module, the effect of the assignment
normally carries over to any programs that included that
file. If the parameter name is preceded by a `*', then the
assignment is automatically undone after the source file
that contains it ends:
{IncludeFrom strings=<p2c/strings.h>}
{*ExportSymbol=pascal_%s}
module strings;
will record the location of the strings module's include
file for the rest of the translation, but the assignment of
ExportSymbol pertains only to the module itself.
For the complete list of p2crc parameters, run p2c with the
-i option. Here are some additional comments on selected
parameters:
ImportAll Because Turbo Pascal only allows one unit per
source file, p2c normally stops reading past
the word implementation in a file being
scanned for interface text. But HP Pascal
allows several modules per file and so this
would not be safe to do. The ImportAll
option lets you override the default behavior
for your Pascal dialect.
AnsiC This parameter selects which dialect of C to
use. If 1, all conventions of ANSI C such as
prototypes, void * pointers, etc. are used.
If 0, only strict K&R (first edition) C is
used. The default is to use "traditional
UNIX C," which includes enum and void but not
void * or prototypes. Once again there are a
number of other parameters which may be used
to control the individual features if just
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setting AnsiC is not enough.
C++ At present p2c does not use much of C++ at
all. The default action is to generate code
that will compile in either language.
UseVExtern Many non-UNIX linkers prohibit variables from
being defined (not declared) by more than one
source file. One module must declare, e.g.,
"int foo;", and all others must declare
"extern int foo;". P2c accomplishes this by
declaring public variables "vextern" in
header files, and arranging for the macro
vextern to expand to extern or to nothing
when appropriate. If you set UseVExtern=0
p2c will instead declare variables in a
simpler way that works only on UNIX-style
linkers.
UseAnyptrMacros
Certain C reserved words have meanings which
may vary from one C implementation to
another. P2c uses special capitalized names
for these words; these names are defined as
macros in the file p2c.h which all translated
programs include. You can set
UseAnyptrMacros=0 to disable the use of these
macros. Note that the functions of many of
these macros can also be had directly using
other parameters; for example, UseConsts
allows you to specify whether your target
language recognizes the word const in
constant declarations. The default is to use
the Const macro instead, so that your code
will be portable to either kind of
implementation.
Signed expands to the reserved word signed if
that word is available, otherwise it is given
a null definition. Similarly, Const expands
to const if that feature is available. The
words Volatile and Register are also defined
in p2c.h, although p2c does not use them at
present. The word Char expands to char by
default, but might need to be redefined to
signed char or unsigned char in a particular
implementation. This is used for the Pascal
character type; lowercase char is used when
the desired meaning is "byte," not
"character."
The word Static always expands to static by
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default. This is used in situations where a
function or variable is declared static to
make it local to the source file; lowercase
static is used for static local variables.
Thus you can redefine Static to be null if
you want to force private names to be public
for purposes of debugging.
The word Void expands to void in all cases;
it is used when declaring a function with no
return value. The word Anyptr is a typedef
for void * or char * as necessary; it
represents a generic pointer.
UsePPMacros The p2c.h header also declares two macros for
function prototyping, PP(x) and PV(). These
macros are used as follows:
Void foo PP( (int x, int y, Char *z) );
Char *bar PV( );
If prototypes are available, these macros
will expand to
Void foo (int x, int y, Char *z);
Char *bar (void);
but if only old-style declarations are
supported, you instead get
Void foo ();
Char *bar ();
By default, p2c uses these macros for all
function declarations, but function
definitions are written in old-style C. The
UsePPMacros parameter can be set to 0 to
disable all use of PP and PV, or it can be
set to 1 to use the macros even when defining
a function. (This is accomplished by
preceding each old-style definition with a
PP-style declaration.) If you know your code
will always be compiled on systems that
support prototyping, it is prettier to set
Prototypes=1 or simply AnsiC=1 to get true
function prototypes.
EatNotes Notes and warning messages containing any of
these strings as sub-strings are not omitted.
Each type of message includes an identifier
like [145]; you can add this identifier to
the EatNotes list to suppress that message.
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Another useful form is to use a variable name
or other identifier to suppress warnings
about that variable. The strings are a
space-separated list, and thus may not
contain embedded spaces. To suppress notes
around a section of code, use, e.g.,
{EatNotes+[145]} and {EatNotes-[145]}. Most
notes are generated during parsing, but to
suppress those generated during output the
string may need to remain in the list far
beyond the point where it appears to be
generated. Use the string "1" or "0" to
disable or enable all notes, respectively.
ExpandIncludes The default action is to expand Pascal
include files in-line. This may not be
desirable if include files are being used to
simulate modules. With ExpandIncludes=0, p2c
attempts to convert include files containing
only whole procedures and global declarations
into analogous C include files. This may not
always work, though; if you get error
messages, don't use this option. By
combining this option with StaticFunctions=0,
then doing some fairly minor editing on the
result, you can convert a pseudo-modular
Pascal program into a truly modular
collection of C source files.
ElimDeadCode Some transformations that p2c does on the
program may result in unreachable or "dead"
code. By default p2c removes such code, but
sometimes it removes more than it should. If
you have "if false" segments which you wish
to retain in C, you may have to set
ElimDeadCode=0.
SkipIndices Normally Pascal arrays not based at zero are
"shifted" down for C, preserving the total
size of the array. A Pascal array a[2..10]
is translated to a C array a[9] with
references like "a[i]" changed to "a[i-2]"
everywhere. If SkipIndices is set to a value
of 2 or higher, this array would instead be
translated to a[11] with the first two
elements never used. This arrangement may
generate incorrect code, though, for tricky
source programs.
FoldConstants Pascal non-structured constants generally
translate to #define's in C. Set this to 1
to have constants instantiated directly into
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the code. This may be turned on or off
around specific constant declarations. Set
this to 0 to force p2c to make absolutely no
assumptions about the constant's value in
generated code, so that you can change the
constant later in the C code without
invalidating the translation. The default is
to allow p2c to take advantage of its
knowledge of a constant's value, such as by
generating code that assumes the constant is
positive.
CharConsts This governs whether single-character string
literals in Pascal const declarations should
be interpreted as characters or strings. In
other words, const a='x'; will translate to
#define a 'x' if CharConsts=1 (the default),
or to #define a x if CharConsts=0. Note that
if p2c guesses wrong, the generated code will
not be wrong, just uglier. For example, if a
is written as a character constant but it
turns out to be used as a string, p2c will
have to write char-to-string conversion code
each time the constant is used.
VarStrings In HP Pascal, a parameter of the form "var s
: string" will match a string variable of any
size; a hidden size parameter is passed which
may be accessed by the Pascal strmax
function. You can prevent p2c from creating
a hidden size parameter by setting
VarString=0. (Note that each function uses
the value of VarStrings as of the first
declaration of the function that is parsed,
which is often in the interface section of a
module.)
Prototypes Control whether ANSI C function prototypes
are used. Default is according to AnsiC.
This also controls whether to include
parameter names or just their types in
situations where names are optional. The
FullPrototyping parameter allows prototypes
to be generated for declarations but not for
definitions (older versions of Lightspeed C
required this). If you use a mixture of
prototypes and old-style definitions, types
like short and float will be promoted to int
and double as required by the ANSI standard,
unless PromoteArgs is used to override this.
The CastArgs parameter controls whether
type-casts are used in function arguments; by
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default they are used only if prototypes are
not available.
StaticLinks HP Pascal and Turbo Pascal each include the
concept of procedure or function pointers,
though with somewhat different syntaxes. P2c
recognizes both notational styles. Another
difference is that HP's procedure pointers
can point to nested procedures, while Turbo's
can point only to global procedures. In HP
Pascal a procedure pointer must be stored as
a struct containing both a pure C function
pointer and a "static link," a pointer to the
parent procedure's locals. (The static link
is NULL for global procedures.) This
notation can be forced by setting
StaticLinks=1. In Turbo, the default
(StaticLinks=0) is to use plain C function
pointers with no static links. A third
option (StaticLinks=2) uses structures with
static links, but assumes the links are
always NULL when calling through a pointer
(if you need compatibility with the HP format
but know your procedures are global).
SmallSetConst Pascal sets are translated into one of two
formats, depending on the size of the set.
If all elements have ordinal values in the
range 0..31, the set is translated as a
single integer variable using bit operations.
(The SetBits parameter may be used to change
the upper limit of 31.) The SmallSetConst
parameter controls whether these small-sets
are used, and, if so, how constant sets
should be represented in C. For larger
sets, an array of long is used. The s[0]
element contains the number of succeeding
array elements which are in use. Set
elements in the range 0..31 are stored in the
s[1] array element, and so on. Sets are
normalized so that s[s[0]] is nonzero for any
nonempty set. The standard run-time library
includes all the necessary procedures for
operating on sets.
ReturnValueName
This is one of many "naming conventions"
parameters. Most of these take the form of a
printf-like string containing a %s where the
relevant information should go. In the case
of ReturnValueName, the %s refers to a
function name and the resulting string gives
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the name of the variable to use to hold the
function's return value. Such a variable
will be made if a function contains
assignments to its return value buried within
the body, so that return statements cannot
conveniently be used. Some parameters
(ReturnValueName included) do not require the
%s to be present in the format string; for
example, the standard p2crc file stores every
function's return value in a variable called
Result.
AlternateName P2c normally translates Pascal names into C
names verbatim, but occasionally this is not
possible. A Pascal name may be a C reserved
word or traditional C name like putc, or
there may be several like-named things that
are hidden from each other by Pascal's
scoping rules but must be global in C. In
these situations p2c uses the parameter
AlternateName1 to generate an alternative
name for the symbol. The default is to add
an underscore to the name. There is also an
AlternateName2 parameter for a second
alternate name, and an AlternateName
parameter for the nth alternate name. (The
value for this parameter should include both
a %s and a %d, in either order.) If these
latter parameters are not defined, p2c
applies AlternateName1 many times over.
ExportSymbol Symbols in the interface section for a Pascal
module are formatted according to the value
of ExportSymbol, if any. It is not uncommon
to use modulename_%s for this symbol; the
default is %s, i.e., no special treatment for
exported symbols. If you also define the
Export_Symbol parameter, that format is used
instead for exported symbols which contain an
underscore character. If %S (with a capital
"S") appears in the format string it stands
for the current module name.
Alias If the value of this parameter contains a %s,
it is a format string applied to the names of
external functions or variables. If the
value does not contain a %s, it becomes the
name of the next external symbol which is
declared (after which the parameter is
cleared).
Synonym This creates a synonym for another Pascal
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symbol or keyword. The format is
Synonym old-name = new-name
All occurrences of old-name in the input text
are treated as if they were new-name by the
parser. If new-name is a keyword, old-name
will be an equivalent keyword. If new-name
is the name of a predefined function, old-
name will behave in the same way as that
function, and so on. If new-name is omitted,
then occurrences of old-name are entirely
ignored in the input file. Synonyms allow
you to skip over a keyword in your dialect of
Pascal that is not understood by p2c, or to
simulate a keyword or predefined identifier
of your dialect with a similar one that p2c
recognizes. Note that all predefined
functions are available at all times; if you
have a library routine that behaves like,
e.g., Turbo Pascal's getmem procedure, you
can make your routine a synonym for getmem
even if you are not translating in Turbo
mode.
NameOf This defines the name to use in C for a
specific symbol. It must appear before the
symbol is declared in the Pascal code; it is
usually placed in the local p2crc file for
the project. The format is
NameOf pascal-name = C-name
By default, Pascal names map directly onto C
names with no change (except for the various
kinds of formatting outlined above). If the
pascal-name is of the form module.name or
procedure.name then the command applies only
to the instance of the Pascal name that is
global to that module, or local to that
procedure. Otherwise, it applies to all
usages of the name.
VarMacro This is analogous to NameOf, but specifically
for use with Pascal variables. The righthand
side can be most any C expression; all
references to the variable are expanded into
that C expression. Names used in the C
expression are taken verbatim. There is also
a ConstMacro parameter for translating
constants as arbitrary expressions. Note
that the variable on the lefthand side must
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actually be declared in the program or in a
module that it uses. The declaration for the
variable will be omitted from the generated
code unless the Pascal-name appears in the
expression: If you ask to replace i with
i+1, the variable i will still be declared
but its value will be shifted accordingly.
Note that if i appears on the lefthand side
of an assignment, p2c will use algebra to
"solve" for i.
In all cases where p2c parses C expressions,
all C operators are recognized except
compound assignments like `+='. (Increment
and decrement operators are allowed.) All
variable and function names are assumed to
have integer type, even if they are names
that occur in the actual program. A type-
specification operator `::' has been
introduced; it has the same precedence as `.'
or `->' but the righthand side must be a
Pascal type identifier (built-in or defined
by your program previously to when the macro
definition was parsed), or an arbitrary
Pascal type expression in parentheses. The
lefthand argument is then considered to have
the specified type. This may be necessary if
your macro is used in situations where the
exact type of the expression must be known
(say, as the argument to a writeln).
FieldMacro Here the lefthand side must have the form
record.field, where record is the Pascal type
or variable name for a record, and field is a
field in that record. The righthand side
must be a C expression generally including
the name record. All instances of that name
are replaced by the actual record being
"dotted." For example,
FieldMacro Rect.topLeft = topLeft(Rect)
translates a[i].topLeft into topLeft(a[i]),
where a is an array of Rect.
FuncMacro The lefthand side must be any Pascal function
or procedure name plus a parameter list. The
number of parameters must match the number in
the function's uses and declaration. Calls
to the function are replaced by the C
expression on the righthand side. For
example,
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P2C(1) (local) P2C(1)
FuncMacro PtInRect(p,r) = PtInRect(p,&r)
causes the second argument of PtInRect to be
passed by reference, even though the
declaration says it's not. If the function
in question is actually defined in the
program or module being translated, the
FuncMacro will not affect the definition but
it will affect all calls to the function
elsewhere in the module. FuncMacros can also
be applied to predefined or never-defined
functions.
IncludeFrom This specifies that a given module's header
should be included from a given place. The
second argument may be surrounded by " " or
< > as necessary; if the second argument is
omitted, no include directive will be
generated for the module.
ImportFrom This specifies that a given module's Pascal
interface text can be found in the given
file. The named file should be either the
source file for the module, or a specially
prepared file with the implementation section
removed for speed. If no ImportFrom entry is
found for a module, the path defined by the
ImportDir list is searched. Each entry in
the path may contain a %s, which expands to
the name of the module. The default path
looks for %s.pas and %s.text in the current
directory, then for /usr/lib/p2c/%s.imp.
(where /usr/lib/p2c is the p2c home
directory.)
StructFunction This parameter is a list of functions which
follow the p2c semantics for structure-valued
functions (functions returning arrays, sets,
and strings, and structs in primitive C
dialects). For these functions, a pointer to
a return-value area is passed to the function
as a special first parameter. The function
stores the result in this area, then returns
a copy of the pointer. (The standard C
function strcpy is an example of this
concept. Sprintf also behaves this way in
some dialects; it always appears on the
StructFunction list regardless of the type of
implementation.) The system configuration
file includes a list of common structured
functions so that p2c's optimizer will know
how to manipulate them.
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P2C(1) (local) P2C(1)
StrlapFunction Functions on this list are structured
functions as above, but with the ability to
work in-place; that is, the same pointer may
be passed as both the return value area and a
regular parameter.
Deterministic Functions on this list have no side effects
or side dependencies. An example is the sin
function in the standard math library; two
calls with the same parameter values produce
the same result, and have no effects other
than returning a value. P2c can make use of
this knowledge when optimizing code for
efficiency or readability. Functions on this
list are also assumed to be relatively fast,
so that it is acceptable to duplicate a call
to the function.
LeaveAlone Functions on this list are not subjected to
the normal built-in translation rules that
p2c would otherwise use. For example, adding
writeln to this list would translate writeln
statements blindly into calls to a C
writeln() function, rather than being
translated into equivalent printf calls. The
built-in translation is also suppressed if
the function has a FuncMacro.
BufferedFile P2c normally assumes binary files will use
read/write, not get/put/^ notation. A file
buffer variable will only be created for a
file if buffer notation is used for it. For
global file variables this may be detected
too late (a declaration without buffers may
already have been written). Such files can
be listed in BufferedFile to force p2c to
allocate buffers for them; do this if you get
a warning message that says it is necessary.
Set BufferedFile=1 to buffer all files, in
which case UnBufferedFile allows you to force
certain files not to have buffers.
StructFiles If p2c still can't translate your file
operations correctly, you can set
StructFiles=1 to cause Pascal files to
translate into structs which include the
usual C FILE pointer, as well as file buffer
and file name fields. While the resulting
code doesn't look as much like native C, the
file structs will allow p2c to do a correct
translation in many more cases.
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P2C(1) (local) P2C(1)
CheckFileEOF Normally only file-open operations are
checked for errors. Additional error
checking, such as read-past-end-of-file, can
be enabled with parameters like CheckFileEOF.
These checks can make the code very ugly! If
I/O checking is enabled by the program
($iocheck on$ in HP Pascal; {$I+} in Turbo;
this is always the default state), these
checks will generate fatal errors unless
enclosed in an HP Pascal try-recover
construct. If I/O checking is disabled,
these will cause the global variable
P_ioresult to be set zero or nonzero
according to the outcome. The default for
most of these options is to check only when
I/O checking is disabled.
ISSUES
Integer size. P2c normally generates code to work with
either 16 or 32 bit ints. If you know your C integers will
be 16 or 32 bits, set IntSize appropriately. In particular
setting IntSize=32 will generate much cleaner code: p2c no
longer must carefully cast function arguments between int
and long. These casts also will be unnecessary if ANSI
prototypes are available. To disable int/long casting
because you know at least one of these cases will hold, set
CastLongArgs=0. (The CastArgs parameter similarly controls
other types of casts, such as between ints and doubles.) The
Integer16 parameter controls whether Pascal integers are
interpreted as 16 or 32 bits, or translated as native C
integers. The default value depends on the Language
selected.
Signed/unsigned chars. Pascal characters are normally
"weakly" interpreted as unsigned; this is controlled by
UnsignedChar. The default is "either," so that C's native
char type may be used even if its signed-ness is unknown.
Code that uses characters outside of the range 0-127 may
need a different setting. Alternatively, you can use the
types {SIGNED} char and {UNSIGNED} char in the few cases
where it really matters. These comments are controlled by
the SignedComment and UnsignedComment parameters. (The type
{UNSIGNED} integer is also recognized.) The SignedChar
parameter tells whether C characters are signed or unsigned
(default is "unknown"). The HasSignedChar parameter tells
whether the phrase "signed char" is legal in the output. If
it is not, p2c may have to translate Pascal signed bytes
into C shorts.
Special types. P2c understands the following predefined
Pascal type names: integer, signed integers depending on
Integer16; longint, signed 32-bit integers; unsigned,
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P2C(1) (local) P2C(1)
unsigned 32-bit integers; sword, signed 16-bit integers;
word, unsigned 16-bit integers; c_int, signed native C
integers; c_uint, unsigned native C integers; sbyte, signed
8-bit integers; byte, unsigned 8-bit integers; real,
floating-point numbers depending on DoubleReals; single,
single-precision floats; longreal, double, and extended,
double-precision floats; pointer and anyptr, generic
pointers (assignment-compatible with any pointer type);
string, generic string of length StringDefault (normally
255); also, the usual Pascal types char, boolean, and text.
(If your Pascal uses different names for these concepts, the
Synonym option will come in handy.)
Embedded code. It is possible to write a Pascal comment
containing C code to be embedded into the output. See the
descriptions of EmbedComment and its relatives in the system
p2crc file. These techniques are helpful if you plan to do
repeated translations of code that is still being maintained
in Pascal.
Comments and blank lines. P2c collects the comments in a
procedure into a list. All comments and statements are
stamped with serial numbers which are used to reattach
comments to statements even after code has been added,
removed, or rearranged during translation. "Orphan"
comments attached to statements that have been lost are
attached to nearby statements or emitted at the end of the
procedure. Blank lines are treated as a kind of comment, so
p2c will also reproduce your usage of blank lines. If the
comment mechanism goes awry, you can disable comments with
EatComments or disable their being attached to code with
SpitComments.
Indentation. P2c has a number of parameters to govern
indentation of code. The default values produce the GNU
Emacs standard indentation style, although p2c can do a
better job since it knows more about the code it is
indenting. Indentation works by applying "indentation
deltas," which are either absolute numbers (which override
the previous indentation), or signed relative numbers (which
augment the previous indentation). A delta of "+0"
specifies no change in indentation. All of the indentation
options are described in the standard p2crc file.
Line breaking. P2c uses an algorithm similar to the TeX
typesetter's paragraph formatter for breaking long
statements into multiple lines. A "penalty" is assigned to
various undesirable aspects of all possible line breaks; the
"badness" of a set of line breaks is approximately the sum
of all the penalties. Chief among these are serious
penalties for overrunning the desired maximum line length
(default 78 columns), an infinite penalty for overrunning
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P2C(1) (local) P2C(1)
the absolute maximum line length (default 90), and
progressively greater penalties for breaking at operators
deeply nested in expressions. Parameters such as
OpBreakPenalty control the relative weights of various
choices. BreakArith and its neighbors control whether the
operator at a line break should be placed at the end of the
previous line or at the beginning of the next. If you don't
want any oversize lines, define MaxLineWidth=78.
Unlike TeX, p2c's line breaker must actually try all
possible sets of break points. To avoid excessive
computation, the total penalty contributed at each decision
point must sum to a nonnegative value; negative values are
clipped up to zero. This allows p2c to prune away obviously
undesirable alternatives in advance. The MaxLineBreakTries
parameter (default 5000) controls how many alternatives to
try before giving up and using the best so far.
PASCAL_MAIN. P2c generates a call to this function at the
front of the main program. In the (unmodified) run-time
library all this does is save argc and argv away because in
both HP and Turbo these are accessed as global variables.
If you do not wish to use this feature, define ArgCName to
be argc, ArgVName to be argv, and MainName (normally
"PASCAL_MAIN") to be blank. This will work if argc and argv
are never accessed outside of your main program.
BUGS
P2c was designed with the idea that clean, readable output
in most cases is worth more than guaranteed correct output
in extreme cases. P2c is not a compiler! However, ideally
the "extreme" cases would include only those which never
arise in real life. Thus if p2c actually generates
incorrect code I will consider it a bug, but I will not
apologize for it. :-) Below are the major remaining cases
where this is known to occur.
Certain kinds of conformant array parameters (including
multi-dimensional conformant arrays) produce code that
declares variable-length arrays in C. Only a few C
compilers, such as the GNU C compiler, support this language
extension. Otherwise some hand re-coding will be required.
HP Pascal try-recover structures are translated into calls
to TRY and RECOVER macros, which are defined to simulate the
construct using setjmp and longjmp. If this emulation does
not work, define the symbol FAKE_TRY to cause these macros
to become "inert." (In cases where the error is detected by
code physically within the body of the try statement, a C
goto to the recover section is always generated.) Also,
local file variables in scopes which are destroyed by an
escape are not closed.
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P2C(1) (local) P2C(1)
Non-local GOTO's and try-recover statements are each
implemented, but may conflict if both are used at once.
Non-local GOTO's are fairly careful about closing files that
go out of scope but may fail to do so in the presence of
recursion.
Arrays containing files are not initialized to NULL as other
files are. In some cases, such as file variables allocated
by NEW, the file is initialized but not automatically closed
by DISPOSE.
LINK variables allowing sub-procedures access to their
parents' variables are occasionally omitted by mistake, if
the access is too indirect for p2c to notice. If this
happens, you can add an explicit reference to a parent
variable in the sub-procedure. A statement of the form
"a:=a" will count as a reference but then be optimized away
by p2c.
Many aspects of Modula-2 are translated only superficially.
For example, the type-compatibility properties of the WORD
and ARRAY OF WORD types are only roughly modelled, as are
the scope rules concerning modules.
Parts of VAX Pascal are still untreated. In particular, the
[UNSAFE] attribute and a few others are not fully supported,
nor are the semantics of the OPEN procedure.
Turbo and VAX Pascal's double, quadruple, and extended real
types all translate to the C double type. Turbo's
computational type is not supported at all.
Because Pascal strings (with length bytes) are translated
into C strings (with null terminators), certain Pascal
string tricks will not work in the translated code. For
example the assignment s[0]:=chr(x) is translated to s[x]=0
on the assumption that the string is being shortened. If x
is actually greater than the current length, but not of a
recognizable form like ord(s[0])+n, then the generated code
will not work. In VAX Pascal this corresponds to performing
arithmetic on the LENGTH field of a varying-length string.
Turbo Pascal's automatic clipping of strings is not
supported. In Turbo, if a ten character string is assigned
to a string[8] variable, the last two characters are
silently removed. The code produced by p2c generally will
overrun the target string instead! The StringTruncLimit
parameter (80 by default if Language=Turbo) specifies a
string size which should be considered "short"; assignments
of potentially-long strings to short string variables will
cause a warning but will not automatically truncate. The
cure is to use copy in the Pascal source to truncate the
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P2C(1) (local) P2C(1)
strings explicitly.
FILES
file.xxx Pascal source files
file.c resulting C source file
module.h resulting C header file
p2crc local configuration file
.p2crc alternate local configuration file
/usr/lib/p2c/p2crc system-wide configuration file
/usr/lib/p2c/system.impdeclarations for predefined functions
/usr/lib/p2c/system.m2 analogous declarations for Modula-2
/usr/lib/p2c/*.imp interface text for standard modules
/usr/include/p2c/p2c.h header file for translated programs
/usr/lib/libp2c.a run-time library
AUTHOR
Dave Gillespie, daveg@csvax.cs.caltech.edu.
Many thanks to William Bader, Steven Levi, Rick Koshi, Eric
Raymond, Magne Haveraaen, Dirk Grunwald, David Barto, Paul
Fisher, Tom Schneider, and others whose suggestions and bug
reports have helped improve p2c in countless ways.
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