Thank you for answers !

To era:

Maybe I was not clear.
Supposed I want to calculate a product of two integers in child process.
So, child.c looks like that:

... some #include

int main(int argc, char *argv[])
{

int a;

int b;

a=atoi(argv[1]);

b=atoi(argv[2]);

return a*b;

}

Under Windows, if I use this code, in parent.c:

int main()
{

int result;

char *args[4];

// prepare arguments for child process

args[0] = "child.exe";

args[1] = argv[1];

args[2] = argv[2];

args[3] = NULL;

// launch the child process

result=_spawnvp (_P_WAIT, args[0], args);

printf("Product: %d, result);

return 0;

}

I'm able to catch the return product from child (a*b) as return from _spawnvp() function in result variable.
Under Linux, posix_spawnp() or wait() return only EXIT_FAILURE or EXIT_SUCCES. I didn't find a way to catch in the parent the product value calculate in the child (value which is returned in child).

To ramen_noodle:
I don't understand you startChild() function.
I don't know what is funion. Is a function or a data type ? I didn't find reference to funion().