Calling C functions from programs

With C-Extensions you can call C functions from the program in the same way that you call normal functions.

The C functions that can be called from programs must use the following signature:

int function-name( int )

function-name must be written in lowercase letters. The fglcomp compiler converts all .4gl module functions names to lowercase.

The C function must be declared in the usrFunctions array in the C interface file.

In the next code example, the C-Extension module "ext1.c" defines the c_fct() function. The C-Extension library is imported by the 4gl module with IMPORT:

#include <stdio.h>
#include <f2c/fglExt.h>
int c_fct( int n )
{
   int r1, r2;
   if (n != 2) ... error ...
   popint(&r1);
   popint(&r2);
   pushint(r1+r2);
   return 1;
}

Genero module calling the C function:

IMPORT ext1
MAIN
   LET x = c_fct(15, 20)
END MAIN