h2pas

Section: Free Pascal C header conversion utility (1)
Updated: 12 Dec 1999
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NAME

h2pas - The C header to pascal unit conversion program.

SYNOPSIS

h2pas [options] filename

DESCRIPTION

h2pas attempts to convert a C header file to a pascal unit. it can handle most C constructs that one finds in a C header file, and attempts to translate them to their pascal counterparts. see the CONSTRUCTS section for a full description of what the translator can handle.

USAGE

H2pas is a command-line tool that translates a C header file to a spascal unit. It reads the C header file and translates the C declarations to equivalent pascal declarations that can be used to access code written in C.

The output of the h2pas program is written to a file with the same name as the C header file that was used as input, but with the extension .pp. The output file that h2pas creates can be customized in a number of ways by means of many options.

OPTIONS

The output of h2pas can be controlled with the following options:

-d: use external; for all procedure and function declarations.
-D: use external libname name 'func_name' for function and procedure declarations.
-e: Emit a series of constants instead of an enumeration type for the C enum construct.
-i: create an include file instead of a unit (omits the unit header).
-l libname: specify the library name for external function declarations.
-o outfile: Specify the output file name. Default is the input file name with the extension replaced by .pp "."
-p: use the letter P in front of pointer type parameters instead of "^".
-s: Strip comments from the input file. By default comments are converted to comments, but they may be displaced, since a comment is handled by the scanner.
-t: prepend typedef type names with the letter T (used to follow Borland's convention that all types should be defined with T).
-v: replace pointer parameters by call by reference parameters. Use with care because some calls can expect a NIL pointer.
-w: Header file is a win32 header file (adds support for some special macros).
-x: handle SYS_TRAP of the PalmOS header files.

CONSTRUCTS

The following C declarations and statements are recognized:

defines

defines are changed into pascal constants if they are simple defines. macros are changed - wherever possible to functions; however the arguments are all integers, so these must be changed manually. Simple expressions in define staments are recognized, as are most arithmetic operators: addition, subtraction, multiplication, division, logical operators, comparison operators, shift operators. The C construct ( A ? B : C) is also recognized and translated to a pascal construct with an IF statement (this is buggy, however).

preprocessor statements

the conditional preprocessing commands are recognized and translated into equivalent pascal compiler directives. The special #ifdef __cplusplus is also recognized and removed.

typedef

A typedef statement is changed into a pascal type statement. The following basic types are recognized:

char: changed to char.
float: changed to real (=double in free pascal).
int: changed to longint.
long: changed to longint.
long int: changed to longint.
short: changed to integer.
unsigned: changed to cardinal.
unsigned char: changed to byte.
unsigned int: changed to cardinal.
unsigned long int: changed to cardinal.
unsigned short: changed to word.
void: ignored.

These types are also changed if they appear in the arguments of a function or procedure.

functions and procedures

functions and procedures are translated as well; pointer types may be changed to call by reference arguments (using the var argument) by using the -p command line argument. functions that have a variable number of arguments are changed to a function with an array of const argument.

specifiers

the extern specifier is recognized; however it is ignored. the packed specifier is also recognised and changed with the PACKRECORDS directive. The const specifier is also recognized, but is ignored.

modifiers

If the -w option is specified, then the following modifiers are recognized: STDCALL , CDECL , CALLBACK , PASCAL , WINAPI , APIENTRY , WINGDIAPI as defined in the win32 headers. If additionally the -x option is specified then the SYS_TRAP specifier is also recognized.

enums

enum constructs are changed into enumeration types; bear in mind that in C enumeration types can have values assigned to them; Free Pascal also allows this to a certain degree. If you know that values are assigned to enums, it is best to use the -e option to change the enus to a series of integer constants.

unions

unions are changed to variant records.

structs

are changed to pascal records, with C packing.