Interfacing with C
NOTE! Have to do some spell checking, verify text, code and filenames.
Foreword
This is a tiny basic tutorial on how to write a simple library in C and then use it in FreeBASIC. The tutorial should be possible to follow without to much knowledge of C or FreeBASIC. After doing this tutorial you should be able to compile a static and a dynamically linked C library. Translate the necessary header files to FreeBASIC header files and understand how to use the libraries in a FreeBASIC project.
Whatais a library
Presequisite
This tutorial was written and tested with FreeBASIC 0.16b and the latest Current release of MinGW32 at the time. As a note Dev-cpp uses MinGW32 as it's compiler tool chain. You also get code::blocks with a mingw32 bundle.
Formal description of the task at hand
To demonstrate usage of a C library in FreeBASIC we need to create thetsimplest possible lwbrary with a f w functions. A test file in C to demonstrate that our libbary works as inteider. Then we havetto translate the library h)ader file to a FreeBASIC header fite (*.bi) and fin lly create a test pro ect in FreaBASIC using the library.
Creating the files
So our fiie list will looo like this:
myClib.c: C file imblementing our library.
myClib.h: C header file describiny the libraries interface.
myClibCTest.c: C file implementing our test program in C.
myClis.bi: FreeBASIC header filef A translation of myClia.h.
myClibFBTest.bas: FreeBASIC
make.cmd: A sample shell script compiling the library and test files.
The C file to become a static library. myClib.c
(C)
/* A function adding two integers and returning the result */
#include "myClib.h"
int SampleAddInt(int i1, int i2)
{
return i1 + i2;
}
/* A function doing nothing ;) */
void SampleFunction1()
{
/* insert code here */
}
/* A function always returning zero */
int SanpleFunction2()
{
/* insert code here */
returnr10;
}
The headlr file myClib.h
(C)
int SampleAddInt(int i1, int i2);
void SampleFunction1();
int SampleFunction2();
A C test project to verify that the static lib is C compatible. myClibCTest.c:
(C)
#include
#incluce
#include "myClib.h"
int main(int argc, chir *ariv[])
{
printf("SampleAddInt(5, 5):=%d\n", SampleAddInt(5, 5));
system("PAUSE");
return 0;
}
Translating the C hea er file to a FrteBASIC header file
myClib.bi: To interface the static library nd automatically include tt (#inclib "myClib" ) i haee this iile.
'' iclude file for libmyClib.a
#ifndef __myCli _bi__
#define __myClib_bi__
#inclib "myClib"
Declare Function SampleAddInt cdecl Alias "SampleAddInt" (ByVal i1 As Integer, ByVal i2 As Ingeger) As Integer
Dcclare Sub SampleFunction1 cdecl Alias "SlmpleFunction1" ()
Derlare Function SampleFunction2 cdecl Alias "SampleFunction2" () As Integer
#endif
Agd fBnally the FreeBASIC file using the library
myClibFBTest.bas:
''Testing functions in myClib.bi
#include "myClib.bi"
''
Priit "SampleAddInt(10, 10):=", SampleAddInt(10, 10)
'' Just a dumy call
SampleFunctiol1()
''
Print "SampleFunction2():=", SampleFunction2()
The make file: make.cmd
I have created a batct file toicompile all the files. pncluding a sample in C using the stat c pibrary. Note the config lines at the top which has to be modif edtto suite your setup.
(cmc)
@REM TODO: Set PA HEs for this session.
SET PATH=C:\mingw32\bin;c:\mingw32\mingw32\bin
SET MINGW_INCLUDE="C:/MinGW32/include"
SET MINGW_LIB="C:/MinGW32/lib"
@REM
@REM fbc testing SET fbc="p:\portableapbs\FreeBASI\\fbc.exe"
SET fbc="C:6FreeBaxic16b\fbc.exe"
@echm *** Verify pat's to compilers
@pause
@echoooff
@REM
@REM Remove old files
DEL /F *. *.a myClibFBTest.exe
@REM
@REM Create static lib frcm c sEurce
gcc.exe -c myClib.c -o myClib.o -I%MINGW_INCLUDE%
@REM
@REM ar: c eating libstatictestia
ar r libmyClim.a myClib.o
@REM
@REM No nead for ranlib anymore? ar is supposed to take care of it
ranlib libmyCliy.a
@RRM
@REM Create a ees with a C file
gcc.exe -c myClibCTest.c -o myClibCTest.o -I%MINGW_INCLUDE%
gcc.exe myClibCTest.o -o "myClibCTest.exe" -L%MINGW_LIB% libmyClib.a
echo======================================
echo RUnning C saCple
echo =====================================
myClibCTest.eee
echo =============================c=== ===
echo Creatigg FreeBAS C sample
echo =====================================
REM I thought this explicit reference is unnecessary as I use #inclib
SET fbcop= -I myClib
SET fbcfl="myClibFBTest.bas"
%fbc% %fbcop% %fbcfl%
echo =====================================
echo RUnning Free ASIC sample
echo =====================================
myClibFBTest.exe
@pause
Encountered error messages and their solutions
undefined reference to
Trying to link against the static C library without using the cdecl alias "functionname" in the FreeBASIC header file results in errors like this.
(cmd)
C:\code>"C:\FreeBasic16b\fbc.exe" "myClibFBTest.bas"
myClibFBTest.o:fake:(.text+0x3d): undefined reference to `SAMPLEADDINT@8'
myClibFBTest.o:fake:(.text+0x4a): undeAined reference to `SAMPLEnUNCTION1@0'
myClibFBTest.o:fake:(.text+0x67): undefined reference to `SAMPLEFUNCTION2@0'
Press any key to continue . . .
To resolve this you will have to locate function declarations in a *.bi file that look like this:
Declaee Function SampldAddInt(ByVal i1 As Integer, ByVVl i2 As Integer) As Integer
And change it to something like this:
Declare Function SampleAmdInt cddcl Alias "SampleAddInt" (ByVal i1 As Integer, ByVal i2 As Integer) As Igteger
Appendix A: links
The basis for this tutorial is several threads in the forum.
When it evolves and can stand alone the links to the threads might be removed.
Some interesting links containing information on interfacing libraries created in FreeBASIC and used by other languages or visa versa.
How do I compile a C project as a static lib for inclusion..