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Introduction

This page describes how to create Pascal bindings for C libraries. In order to use C libraries in Pascal, you have to create a pascal translation for every C function, type and variable. To do that one can either utilized an automated tool, like h2pas or do a manual headers conversion

H2PAS

Overview

The H2Pas tool that automatically translates many common C things. A GUI for Lazarus using h2pas and other tools additionally automates the creation. It helps to create a rule set, which can be used to update the bindings. So the next version of the c library can be converted far more easier. A nice feature of the h2pas wizard is that it uses temporary files, so the c header files remain unchanged.

Work flow

Fetch the C header files you want to translate.
Create a working directory and give your bindings a name
Create a new h2pas project with the h2pas wizard.
Add the .h files to the project.
Setup the h2pas options.
Run the wizard.
Fix errors by adding text tools and run the wizard again.
When h2pas runs without errors, test compilation and add optional tools to beautify the output.
Write some test programs to test your bindings.
Publish your bindings on lazarus-ccr or the FreePascal website.

Install tools

The h2pas tool comes with every normal fpc installation.

Install the h2paswizard package in the Lazarus IDE. Go to "Package->Install/Uninstall Packages", select from the right list the H2PasWizard package and click 'Install selection', then 'Save and rebuild IDE'. Restart the IDE and you get a new menu entry: Tools -> h2pas

Fetch C header files

The C header files .h describes the interface of a C library. They are normally not provided with the library. You have to get the sources or the development package of the library. For example the C header files of the gtk libraries are in the package gtk+-devel.

Example: MPICH2

Download the mpich2-1.0.3.tar.gz from http://www-unix.mcs.anl.gov/mpi/mpich2/ and unpack them. The .h files are under mpich2-1.0.3/src/include.

You can find more information about MPICH for FPC here.

Create a working directory and name your bindings

Create a directory with a useful name. A name should not contain special characters, like spaces, umlaute, points or commas. Copy the .h files.

Example: MPICH2

The h2p directory will be used for the pascal files. The h2p/c_sources directory will be used for the .h files.

mkdir -p h2p/c_sources
cp mpich2-1.0.3/src/include/*.h h2p/c_sources/

Create a new h2pas project with the h2pas wizard

Open the h2pas wizard: "Tools -> h2pas". This will open a window. You can switch between this window and the other IDE windows. Your last h2pas project will be loaded automatically. To create a new project click on "Settings -> New/Clear settings". Then click on the bottom button "Save settings" and choose a filename.

Note: If this is the first time you have used the h2pas wizard, you need to use the wizard's "Settings" tab to tell the wizard where to find the h2pas.exe converter program. The h2pas.exe converter lives in the same directory as the FreePascal compiler fpc.exe - if you downloaded FPC as part of Lazarus it will be in ...\Lazarus\fpc\version\bin. Then save the settings so you don't have to do this again.

Example: MPICH2

Click on "Settings -> New/Clear settings". Then click on the bottom button "Save settings" and save it as h2p/mpi2.h2p.

Add the .h files to the h2pas-project

In the "C header files" page you can add/delete the .h files. You can enable/disable .h files to convert only part of the files.

Example: MPICH2

Click on "C header files -> Add .h files ..." and select "mpi.h" and "mpio.h". They will be enabled automatically. Select the mpi.h file and click "Merge all but this", so that the wizard combines all header files into one unit (mpi.pas).

Setup the h2pas options

Under "h2pas Options" you can set the parameters for the h2pas program.

Example: MPICH2

Enable -e, -D, -p, -w and disable all others.
The -l library path is "mpich".
Output extension is ".pas"
Output directory is h2pas/, which is the default, so leave it empty

Run the wizard

Click on the bottom button "Run h2pas". This will copy the <example>.h file to a temporary <example>.tmp.h file and run the tools listed under "Before h2pas". Then it runs h2pas to convert the <example>.tmp.h into <example>.inc or <example>.pas or whatever output extension you setup on the h2pas page. Then it runs the tools listed under "After h2pas" on the output files.

If h2pas finds a syntax error, the IDE will open the example.tmp.h file and jumps to the error line. h2pas often only reports 'syntax error', which is very unspecific. See Common problems when converting C header files.

Example: MPICH2

The h2pas wizard already contains all tools to convert all the specials of this header file, so h2pas runs without errors. But the created unit is not yet ready. Read further.

Go to the After H2Pas tab and add the Reduce compiler directives in pascal file tool.

Add the following to the Undefines property:

 MPI_INCLUDED
 MPIO_INCLUDE
 NEEDS_MPI_FINT
 MPI_BUILD_PROFILING
 MPICH_SUPPRESS_PROTOTYPES
 MPI_Wtime
 HAVE_MPICH2G2
 FOO
 HAVE_PRAGMA_HP_SEC_DEF

Add the following to the Defines property:

 MPICH2
 MPICH_NEW_MPIIO

Writing your own converter tools

Using the tool "Search and replace"

Many things like renaming a variable can be done by the Search and replace tool. Add the tool via the Add new tool button on either the 'Before h2pas' or the 'After h2pas' page. Then set the SearchFor, ReplaceWith, Options and Caption property.

Option: trtRegExpr

If you set this option to True, it means that you want to use regular expressions. This allows for plenty of possibilities to adapt and/or beautify the source code by metacharacters and quantifiers. A list of the metacharacters and quantifiers and examples are found in this article: IDE_regular_expressions.

Example: rename an identifier Tguint to guint

Property	Value
Caption	Rename Tguint to guint
SearchFor	Tguint
ReplaceWith	guint
Options	[trtMatchCase,trtWholeWord]

Example: rename several identifiers

Rename Tguint to guint, Tgulong to gulong, Tgint to gint:

Property	Value
Caption	Rename Tguint to guint
SearchFor	T(guint\|gint\|gulong)
ReplaceWith	$1
Options	[trtMatchCase,trtWholeWord,trtRegExpr]

Example: MPICH2

Removing Makro MPI_DUP_FN

The MPI_DUP_FN is defined two times in the mpi C headers. Once as a macro to something that does not exist, and later to a real function. So, the first should be deleted.

Add a 'Search and replace' tool to the before H2Pas tools (at the end) with the following settings:

Property	Value
Caption	Remove dummy define MPI_DUP_FN
Name	RemoveDummyDefineMPI_DUP_FN
SearchFor	^#define\s+MPI_DUP_FN\s+MPIR_Dup_fn
ReplaceWith
Options	[trtMatchCase,trtRegExpr]

Removing typecasts to MPI_DUP_FN

Add a 'Search and replace' tool to the before H2Pas tools (at the end) with the following settings:

Property	Value
Caption	Remove MPI_DUP_FN Makros
Name	Remove_MPI_DUP_Func
SearchFor	^#define .MPI_DUP_FN\).$
ReplaceWith
Options	[trtMatchCase,trtRegExpr]

Removing functions MPIO_Test, PMPIO_Test, MPIO_Wait and PMPIO_Wait

The MPIO_Test, PMPIO_Test, MPIO_Wait and PMPIO_Wait functions are defined twice and redefined via macro. So, the functions can be removed:

Add a 'Search and replace' tool to the before H2Pas tools (at the end) with the following settings:

Property	Value
Caption	Remove Func P?MPIO_(Test\|Wait)
Name	RemoveFuncP_MPIO_Test_Wait
SearchFor	^int P?MPIO_(Test\|Wait).*$
ReplaceWith
Options	[trtMatchCase,trtRegExpr]

Improving an existing tool

You found a bug and want to fix it or you want to extend one of the above tools. Great!

Most of the above tools are defined in the h2pasconvert unit, which is part of the h2paswizard package. Basically a tool needs a classname, a description and an Execute method. To test/debug a tool outside the IDE and save a lot of compilation time, see the project components/simpleideintf/examples/testh2pastool.lpi. Compile it and start it on a console/terminal with the filename of a .h file as first command parameter. For example:

./testh2pastool files/h2pastest.pas

Writing a custom tool

You can write your own conversion tools and register them in the IDE easily. Start a package and a add a new unit (say unit1) for your new class. See the existing tools as example and read the prior section. When you wrote a new tool and tested it with the above simpleideintf project, then register it in the IDE: Add a register procedure to your unit (unit1), like the following (pseudo code):

uses
  Classes, ..., IDETextConverter;

type
  TYourToolClass = class(TCustomTextConverterTool)
  public
    class function ClassDescription: string; override;
    function Execute(aText: TIDETextConverter): TModalResult; override;
  end;

procedure Register;

implementation

procedure Register;
begin
  TextConverterToolClasses.RegisterClass(TYourToolClass);
end;

Do not forget to enable the register checkbox of the unit in the package editor, otherwise the Register procedure will not be called by the IDE. Then install your package in the IDE.

Future work / Missing stuff

A tool to convert static linked procedures to dynamic linked procedure variables
A tool to fix functions without parameter names by searching the .c files. This could also add a comment, in which c file it found the function.
Find missing identifiers and let the user check which one to comment or replace with base types.
Create a list of macro functions, which were half translated.

C:

typedef struct page
{
   u32int present    : 1;   // Page present in memory
   u32int rw         : 1;   // Read-only if clear, readwrite if set
   u32int user       : 1;   // Supervisor level only if clear
   u32int accessed   : 1;   // Has the page been accessed since last refresh?
   u32int dirty      : 1;   // Has the page been written to since last refresh?
   u32int unused     : 7;   // Amalgamation of unused and reserved bits
   u32int frame      : 20;  // Frame address (shifted right 12 bits)
} page_t;

Pascal:

type
    Unsigned_7  = 0 .. (1 shl 7)  - 1;
    Unsigned_20 = 0 .. (1 shl 20) - 1;

type
    page_t = bitpacked record
       present  : boolean;
       rw       : boolean;
       user     : boolean;
       accessed : boolean;
       dirty    : boolean;
       unused   : Unsigned_7;
       frame    : Unsigned_20;
    end;

Convert C to Pascal with lua script

I'm impressed by the power of the lua scripting language and how easy it is to do funny things with it.

--
-- Please send any improvement to mingodadATgmailDOTcom.
--

inFileName = arg[1] or 'g:\\tmp\\plua\\clua\\lvm.c'

fh = assert(io.open(inFileName))
cbody = fh:read('*a')
fh:close()

pasbody = cbody

function split(str, pat)
   local t = {}  -- NOTE: use {n = 0} in Lua-5.0
   local fpat = '(.-)' .. pat
   local last_end = 1
   local s, e, cap = str:find(fpat, 1)
   while s do
      if s ~= 1 or cap ~= '' then
	table.insert(t, cap)
      end
      last_end = e+1
      s, e, cap = str:find(fpat, last_end)
   end
   if last_end <= #str then
      cap = str:sub(last_end)
      table.insert(t, cap)
   end
   return t
end

function trim(s)
  -- from PiL2 20.4
  return (s:gsub('^%s*(.-)%s*$', '%1'))
end

function trimChars(str, c1, c2)
	return str:gsub('^%' .. c1 .. '*(.-)%' .. c2 .. '*$', '%1')
end

function getPascalType(cType)
	if cType == 'void' then
		return 'pointer'
	elseif cType == 'int' then
		return 'integer'
	elseif cType == 'short' then
		return 'Shortint'
	elseif cType == 'define' then
		return 'is_define'
	else
		return cType
	end
end


--check var name and type
--if var starts with a capital letter
-- add 'T' informt of it
--if var is preceded by * then add a 'P' for type

function checkVarType(aType, aVar)
	aType = getPascalType(aType)
	aType = aType:gsub('^(%u)', 'T%1')
	aVar = aVar:gsub('^(%*)', function(m)
			aType = 'P' .. aType
			return ''
		end)
	aVar = aVar:gsub('(%[[^]]+%])', function(m)
			aType = 'array' .. m .. ' of ' .. aType
			return ''
		end)
	return aType, aVar
end

function varDeclaration(aType, aVar)
	aType, aVar = checkVarType(aType, aVar)
	return aVar .. ' : ' .. aType
end

function checkDeclarationOrGoto(m1, m2, m3)
	if m2 ~= 'goto' then
		return '\n' .. m1 .. varDeclaration(m2, m3) .. ';'
	else
		return '\n' .. m1 .. m2 .. ' ' .. m3 .. ';'
	end
end

function addProcFunc(mtype, mname, mparams, mbody)
	local str, isFunc, rType, k, v
	if mtype == 'void' then
		str = '\nprocedure '
		isFunc = false
	else
		str = '\nfunction '
		isFunc = true
	end
	mtype, mname = checkVarType(mtype, mname)
	local vparams = split(trimChars(mparams, '(',')'), ',')
	str = str .. mname .. '('

	local tparams = {}
	for k, v in pairs(vparams) do
		local vparam = split(trim(v), ' ')
		if #vparam > 2 then
			table.insert(tparams, vparam[1] .. ' ' .. varDeclaration(vparam[2], vparam[3]))
		else
			--print(vparam[1], vparam[2])
			table.insert(tparams, varDeclaration(vparam[1], vparam[2] or 'is_define'))
		end
	end

	str = str .. table.concat(tparams, '; ') .. ')'
	if isFunc then
		if mtype == 'int' then
			rType = 'integer'
		else
			rType = mtype
		end
		str = str .. ':' .. rType
	end

	if mbody then
		local tblLabels = {}
		for v in mbody:gmatch('\n[\t ]*([%w_]+)[\t ]*:[^=]') do
			if v ~= 'default' then
				table.insert(tblLabels, v)
			end
		end

		if #tblLabels > 0 then
			str = str .. ';\nlabel\n  '.. table.concat(tblLabels, ',  ')
		end

		local declarations = {}

		mbody = mbody:gsub('(\n[\t ]*)const[\t ]+([%w_]+)[\t ]+(%*?[%w_]+)[\t ]*:%=[\t ]*([^;\n]+;)','%1 %2 %3 := %4')

		mbody = mbody:gsub('(\n[\t ]*)([%w_]+)[\t ]+(%*?[%w_]+)[\t ]*:%=[\t ]*([^;\n]+;)', function(m1, m2, m3, m4)
			table.insert(declarations, varDeclaration(m2, m3) .. ';' )
			return m1 .. m3 .. ' := ' .. m4
		end)

		mbody = mbody:gsub('\n[\t ]*const[\t ]*([%w_]+)[\t ]+(%*?[%w_]+)[\t ]*;', function(m1,m2)
				table.insert(declarations, varDeclaration(m1, m2) .. ';')
				return ''
			end)

		mbody = mbody:gsub('\n([\t ]*)([%w_]+)[\t ]+(%*?[%w_ ,]+);', function(m1,m2,m3)
				if m2 ~= 'goto' then
					table.insert(declarations, varDeclaration(m2, m3) .. ';')
					return ''
				else
					return '\n' .. m1 .. m2 .. ' ' .. m3 .. ';'
				end
			end)


		if #declarations > 0 then
			local unique_decl = {}
			table.sort(declarations)
			local lastV = ''
			local k2, v2
			for k2,v2 in pairs(declarations) do
				if v2 ~= lastV then
					lastV = v2
					table.insert(unique_decl, v2)
				end
			end
			str = str .. ';\nvar\n  '.. table.concat(unique_decl, '\n  ')  .. '\n'
		else
			str = str .. ';\n'
		end

		str = str .. 'begin' .. trimChars(mbody, '{','}') .. 'end'
	end
	return str .. ';'
end

--*************************************
--
-- Order of substitutions are important
--
--*************************************

--=assignements statements
	pasbody = pasbody:gsub("([\t ]*)([%w_]+)[\t ]*=[\t ]*([^=;\n]+);", '%1%2 := %3;')

--return
	pasbody = pasbody:gsub('([\t ]*)return[\t ]+([^;]+);', '%1exit(%2);')

--NULL
	pasbody = pasbody:gsub('([^%w]+)NULL([^%w]+)', '%1nil%2')

--void functions to procedure declaratios
	pasbody = pasbody:gsub('([%w_*]+)[\t ]+([%w_*]+)[\t ]*(%b())[%s]*(%b{})', addProcFunc)
	--pasbody = pasbody:gsub('\n([%w_]+)%s+([^%s]+)%s*(%b());', addProcFunc)

--const/static
	tblLeaveCommented = {
		'const', 'static'
	}
	for k,v in pairs(tblLeaveCommented) do
		pasbody = pasbody:gsub('([\t ]*)(' .. v .. ')([\t ]*)', '%1{%2}%3')
	end

--defines to const
	isConstEmmited = false
	function addConst(m1,m2)
		local sm
		sm = ''
		if not isConstEmmited then
			isConstEmmited = true
			sm = '\nconst'
		end
		return sm .. '\n\t' .. m1 .. ' = ' .. m2 .. ';'
	end

	isConstEmmited = false
	pasbody = pasbody:gsub('\n#define%s+([^%s]+)%s+(%b())', '\nconst %1 = %2;')
	isConstEmmited = false
	pasbody = pasbody:gsub('\n#define%s+([^%s]+)[ \t]+([^%s]+)', '\nconst %1 = %2;')

--includes
	tblUses = {}
	pasbody = pasbody:gsub('\n#[ \t]*(include)%s+([^\n]+)', function(m1,m2)
			for w in m2:gmatch('"([^.]+)%..+"') do
				table.insert(tblUses, w)
			end
			return '\n//#' .. m1 .. ' ' .. m2
		end)
	pasbody = '//uses ' .. table.concat(tblUses, ', ') .. ';\n' .. pasbody

--defines to compiler directives
	pasbody = pasbody:gsub('\n#([^\n]+)', '\n{$%1}')

--comments
	pasbody = pasbody:gsub('\n#', '\n//#')
	pasbody = pasbody:gsub('/%*', '(*')
	pasbody = pasbody:gsub('%*/', '*)')

--declarations
	pasbody = pasbody:gsub('\n([\t ]*)([%w_]+)[\t ]+([%w_ ,]+);', checkDeclarationOrGoto)

--structs
	function parseStruct(m1, m2)
		return '\n' .. m1 .. ' = record\n' .. trimChars(m2, '{', '}') .. '\nend'
	end
	pasbody = pasbody:gsub('\n[\t ]*struct[\t ]+([%w_]+)[\t ]*(%b{})', parseStruct)

--if statements
	parseStatementCalled = false

	function parseStatement(mSpace, mStatement, mCond, mBody)
		parseStatementCalled = true
		local vStatement
		if mStatement == 'if' then
			vStatement = mStatement .. ' ' .. mCond .. ' then'
		elseif mStatement == 'else' then
			return mSpace .. mStatement .. ' begin' .. trimChars(mCond, '{', '}') .. ' end;'
		elseif (mStatement == 'while') then
			vStatement = mStatement .. ' ' .. mCond .. ' do'
		elseif (mStatement == 'for') then
			vStatement = mStatement .. ' ' .. mCond .. ' do'
			--local forArgs = split(trimChars(mCond, '(', ')'), ';')
			--return mSpace .. (forArgs[1] or '') .. ';' .. mSpace ..'while (' ..
			--	(forArgs[2] or 'true') .. ') do' .. mSpace .. 'begin' .. mSpace .. trimChars(mBody, '{', '}') .. '\n' .. mSpace ..
			--	(forArgs[3] or '') .. ';\n' .. mSpace .. 'end;'
		else
			vStatement = mStatement .. ' ' .. mCond .. '\n'
		end
		return mSpace .. vStatement .. ' begin' ..  trimChars(mBody, '{', '}') .. 'end;'
	end

	-- for nested blocks
	parseStatementCalled = true
	while(parseStatementCalled) do
		parseStatementCalled = false
		pasbody = pasbody:gsub('([^%w_])(if)[\t ]*(%b())[\t ]*(%b{})', parseStatement)
	end

	-- else
	pasbody = pasbody:gsub('([\t ]+)(else)[\t ]*(%b{})', parseStatement)

	pasbody = pasbody:gsub("([^%w_])if[\t ]*(%b())[\t ]*([^;\n]+);", '%1if %2 then %3;')

--?: short if
	pasbody = pasbody:gsub("([^?])?([^:;\n]):[\t ]*([^%s;]+);", ' iff(%1, %2, %3) ')

--while loop
	-- for nested blocks
	parseStatementCalled = true
	while(parseStatementCalled) do
		parseStatementCalled = false
		pasbody = pasbody:gsub('([^%w_])(while)[\t ]*(%b())[\t ]*(%b{})', parseStatement)
	end

--for loop
	-- for nested blocks
	parseStatementCalled = true
	while(parseStatementCalled) do
		parseStatementCalled = false
		pasbody = pasbody:gsub('([^%w_])(for)[\t ]*(%b())%s*(%b{})', parseStatement)
	end

--do/while
	-- for nested blocks
	parseStatementCalled = true
	while(parseStatementCalled) do
		parseStatementCalled = false
		pasbody = pasbody:gsub("([^%w_])do[\t ]*(%b{})[\t ]*while([^;\n]+);",
			function(m1, m2, m3)
				parseStatementCalled = true
				return m1 .. 'repeat ' .. trimChars(m2, '{', '}') .. 'until not' .. m3
			end)
	end


--switch/case statements

	--begin/end enclose blocks around
	-- for nested blocks
	parseStatementCalled = true
	while(parseStatementCalled) do
		parseStatementCalled = false
		pasbody = pasbody:gsub("([^%w_]case[\t ]+[^:]+)[\t ]*:[%s]*(%b{})",
			function(m1, m2, m3)
				parseStatementCalled = true
				return m1 .. ': begin' .. trimChars(m2, '{', '}') .. 'end;'
			end)
		pasbody = pasbody:gsub("([^%w_]default[\t ]*):[%s]*(%b{})",
			function(m1, m2, m3)
				parseStatementCalled = true
				return m1 .. ': begin' .. trimChars(m2, '{', '}') .. 'end;'
			end)
	end

	--breaks remove
	pasbody = pasbody:gsub("([^%w_]case[\t ]+[^:]+)[\t ]*:[%s]*(.-)break;", '%1: %2')

	--case
	pasbody = pasbody:gsub("([^%w_])case[\t ]+([^:]+):", '%1%2:')

	-- for nested blocks
	parseStatementCalled = true
	while(parseStatementCalled) do
		parseStatementCalled = false
		pasbody = pasbody:gsub("([^%w_])switch[\t ]*(%b())[\t ]*(%b{})",
			function(m1, m2, m3)
				parseStatementCalled = true
				return m1 .. 'case ' .. m2 .. ' of ' .. trimChars(m3, '{', '}') .. 'end;'
			end)
	end

	--pasbody = pasbody:gsub("([\t ]*)case[\t ]+('.')[\t ]*:\n", '%1%2:\n')
	--pasbody = pasbody:gsub("([\t ]*)case[\t ]+(%d+)[\t ]*:\n", '%1%2:\n')
	--pasbody = pasbody:gsub("([\t ]*)(case)[\t ]+('.')[\t ]*:[\t ]*(%b{})", '%1%2 : %3')

--pre/pos increments
	-- (n)++ -> PosInc(n)
	pasbody = pasbody:gsub("(%([^%s+]+%))%+%+", 'PosInc%1')
	-- n*++ -> PosInc(n*)
	pasbody = pasbody:gsub("([^%s*+]+)%+%+", 'PosInc(%1)')
	-- ++(n) -> PreInc(n)
	pasbody = pasbody:gsub("%+%+(%([^%s;+]+%))", 'PreInc%1')
	-- ++*n -> PreInc(n)
	pasbody = pasbody:gsub("%+%+([^%s*;+]+)", 'PreInc(%1)')

	-- (n)--
	pasbody = pasbody:gsub("(%([^%s-]+%))%-%-", 'PosDec%1')
	-- n*--
	pasbody = pasbody:gsub("([^%s*-]+)%-%-", 'PosDec(%1)')
	-- --(n)
	pasbody = pasbody:gsub("%-%-(%([^%s;-]+%))", 'PreDec%1')
	-- --n
	pasbody = pasbody:gsub("%-%-([^%s;-]+)", 'PreDec(%1)')

--boolean operators
	tblBooleanOperators = {
		{'||', 'or'},
		{'&&', 'and'},
	}
	for k,v in pairs(tblBooleanOperators) do
		pasbody = pasbody:gsub('([\t ]*)' .. v[1] .. '([\t ]*)', '%1) ' .. v[2] .. ' (%2')
	end


--pointers
	pasbody = pasbody:gsub("%->", '.')
	pasbody = pasbody:gsub("%(%*([%w_]+)", '(%1^')
	pasbody = pasbody:gsub("%*%*([%w_]+)", '%1^^')
	pasbody = pasbody:gsub("&([%w_]+)", '@%1')
	pasbody = pasbody:gsub("%*([%w_]+)[\t ]*:[\t ]*([%w_]+);", '%1 : ^%2;')
	pasbody = pasbody:gsub("%^char", 'pchar')
	--pasbody = pasbody:gsub("%*([%w_]+)[\t ]*:=[\t ]*([^;\n]+);", '%1^ := %2;')

--bit operators
	tblBitOperators = {
		{'<<', 'shl'},
		{'>>', 'shr'},
		{'|', 'or'},
		{'&', 'and'},
		{'~', 'not'},
	}

	for k,v in pairs(tblBitOperators) do
		pasbody = pasbody:gsub('([\t ]*)' .. v[1] .. '([\t ]*)', '%1 ' .. v[2] .. ' %2')
	end

--==eq operator
	pasbody = pasbody:gsub("([\t ]*)%=%=([\t ]*)", '%1 = %2')

--!= not eq operator
	pasbody = pasbody:gsub("([\t ]*)!%=([\t ]*)", '%1 <> %2')

--! unary
	pasbody = pasbody:gsub('([\t ]*)!([\t ]*)', '%1 not %2')

--blocks
	--pasbody = pasbody:gsub("(%b{})", function(m1) return 'begin' ..  trimChars(m1, '{', '}') .. 'end;' end)
	--pasbody = pasbody:gsub("(%b{})", function(m1) return 'begin' ..  trimChars(m1, '{', '}') .. 'end;' end)

--strings and escaped characters
	tblEscapedCahrs = {
		{'\\"', '"'},
		{'\\\\', '\\'},
		{'\\t', "'#9"},
		{'\\n', "'#10'"},
		{'\\f', "'#12'"},
	}
	pasbody = pasbody:gsub('%b""', function(m1)
			return "'" .. trimChars(m1:gsub("'", "''") , '"', '"')  .. "'"
		end)
	for k,v in pairs(tblEscapedCahrs) do
		pasbody = pasbody:gsub(v[1], v[2])
	end

--common functions/procedure
	tblOrigFuncNewFunc = {
		{'printf', 'format'},
		{'malloc', 'GetMem'},
		{'free', 'Dispose'},
		{'memcpy', 'Move'},
	}

	for k,v in pairs(tblOrigFuncNewFunc) do
		pasbody = pasbody:gsub('([\t ]+)' .. v[1] .. '%(', '%1' .. v[2] .. '(')
	end

--typedefs
	isTypeEmmited = false
	function addType(m1,m2)
		local sm
		sm = ''
		if not isTypeEmmited then
			isTypeEmmited = true
			sm = '\ntype'
		end
		return sm .. '\n\t' .. m2 .. ' = ' .. m1 .. ';'
	end
	--pasbody = pasbody:gsub('\ntypedef%s+struct%s+([^%s]+)%s+([^;]+)', addType)
	--pasbody = pasbody:gsub('\ntypedef%s+([^%s]+)%s+([^;]-)', addType)
	pasbody = pasbody:gsub('\n[\t ]*typedef[\t ]+struct[\t ]+([%w_]+)[\t ]+([^;]+)', '\n%2 = %1')
	pasbody = pasbody:gsub('\n[\t ]*typedef[\t ]+struct%s+(%b{})%s+([%w_]+);',
		function(m1, m2) return m2 .. ' = record' .. trimChars(m1, '{', '}') .. 'end;' end)


-- print the results
print(pasbody)

Here is an example of a c file converted.

//uses lua, llimits, lmem, lstate, lzio;
(*
** $Id: lzio.c,v 1.31.1.1 2007/12/27 13:02:25 roberto Exp $
** a generic input stream interface
** See Copyright Notice in lua.h
*)


//#include <string.h>

{$define lzio_c}
{$define LUA_CORE}

//#include 'lua.h'

//#include 'llimits.h'
//#include 'lmem.h'
//#include 'lstate.h'
//#include 'lzio.h'



function luaZ_fill(z : PTZIO):integer;
var
  L : Plua_State;
  buff : Pchar;
  size : size_t;
begin
  *L := z.L;
  lua_unlock(L);
  buff := z.reader(L, z.data, @size);
  lua_lock(L);
  if (buff  =  nil ) or ( size  =  0) then exit(EOZ);
  z.n := size - 1;
  z.p := buff;
  exit(char2int(PosInc^((z.p))));
end;



function luaZ_lookahead(z : PTZIO):integer;
begin
  if (z.n  =  0) then begin
    if (luaZ_fill(z)  =  EOZ)
      exit(EOZ);
    else begin
      PosInc(z.n);  (* luaZ_fill removed first byte; put back it *)
      z-PosDec(>p);
     end;
  end;
  exit(char2int(z^.p));
end;



procedure luaZ_init(L : Plua_State; z : PTZIO; reader : lua_Reader; data : Ppointer);
begin
  z.L := L;
  z.reader := reader;
  z.data := data;
  z.n := 0;
  z.p := nil;
end;


(* --------------------------------------------------------------- read --- *)

function luaZ_read(z : PTZIO; b : Ppointer; n : size_t):size_t;
var
  m : size_t;
begin
  while (n) do begin
    if (luaZ_lookahead(z)  =  EOZ)
      exit(n);  (* exit(number of missing bytes *)
    m = (n <= z.n) ? n : z.n);  (* min. between n and z.n *)
    Move(b, z.p, m);
    z.n -= m;
    z.p += m;
    b := (char *)b + m;
    n -= m;
  end;
  exit(0);
end;

(* ------------------------------------------------------------------------ *)

function luaZ_openspace(L : Plua_State; buff : PTMbuffer; n : size_t):Pchar;
begin
  if (n > buff.buffsize) then begin
    if (n < LUA_MINBUFFER) then n := LUA_MINBUFFER;
    luaZ_resizebuffer(L, buff, n);
  end;
  exit(buff.buffer);
end;

Manual conversion of C headers to Pascal

In this case one should utilize ones knowledge of C and Pascal together to make the headers. One can learn how to do the conversion by looking at examples.

Converting constants

C:

#define SOME_CONSTANT 5
#define ANOTHER_CONSTANT 6

Pascal:

const
  SOME_CONSTANT = 5;
  ANOTHER_CONSTANT = 6;

Converting exported routines

The most basic routines can be translated like this:

C:

int somekind_of_method(int* param_first, int* param_second)
void another_method(char*)

Pascal:

uses ctypes;

const
  MyLib = 'mylib';

function somekind_of_method(param_first, param_second: pcint): cint; external MyLib;
procedure another_method_renamed(param1: PChar); external MyLib name 'another_method';

Note that one should use the ctypes unit together with the types that it declares to convert C headers instead of trying to use the basic Pascal types directly. This ensures that the bindings are correct in all platforms, as the C types might have different sizes on different architectures and operating systems.

Also, note that pointers to basic C types can be converted to types declared in ctypes, for example, int* is a pointer to a C int, so we can use the type pcint (pointer to a c integer). The C type int can be converted to cint and in Pascal we can shorten the declaration of parameters which are declared one after as folows: "param_first, param_second: pcint".

Finally, note that if the return value is void, then we should use a procedure instead of function.

Creating Pascal bindings for C is a tutorial with source code that explains in detail how to create manual bindings for C libraries. It deals with various data types (strings, arrays, etc). The tutorial also demonstrates how to create static (*.a) and shared/dynamic libraries (*.so or *.dll) libraries using the MinGW C compiler. Using this approach in combination with h2pas can be quite efficient.

See also the [External Functions] section of the reference guide.

Publish your bindings on Lazarus-CCR or Free Pascal

You can submit your binding code to the Lazarus CCR repository (see e.g. Using_the_Lazarus-ccr_SVN_repository) so others can use (and maintain) it, too. If the bindings are useful for general, cross-platform work, they could be included in the FreePascal distribution as well.

Creating bindings for C libraries

Introduction

H2PAS

Overview

Work flow

Install tools

Fetch C header files

Example: MPICH2

Create a working directory and name your bindings

Example: MPICH2

Create a new h2pas project with the h2pas wizard

Example: MPICH2

Add the .h files to the h2pas-project

Example: MPICH2

Setup the h2pas options

Example: MPICH2

Run the wizard

Example: MPICH2

Writing your own converter tools

Using the tool "Search and replace"

Option: trtRegExpr

Example: rename an identifier Tguint to guint

Example: rename several identifiers

Example: MPICH2

Removing Makro MPI_DUP_FN

Removing typecasts to MPI_DUP_FN

Removing functions MPIO_Test, PMPIO_Test, MPIO_Wait and PMPIO_Wait

Improving an existing tool

Writing a custom tool

Future work / Missing stuff

Convert C to Pascal with lua script

Manual conversion of C headers to Pascal

Converting constants

Converting exported routines

Publish your bindings on Lazarus-CCR or Free Pascal

See also

Navigation menu

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