MLSetYieldFunction()

#include "mathlink.h"

int AppYieldFunction(MLINK lp, MLYieldParameters yp)
{
    /* ... */
    return 0;
}

int main(int argc, char **argv)
{
    MLENV env;
    MLINK link;
    int error;

    env = MLInitialize((MLParametersPointer)0);
    if(env  (MLENV)0)
        { /* unable to initialize MathLink environment */ }

    link = MLOpenArgcArgv(env, argv, argv + argc, &error);
    if(link  (MLINK)0 || error  MLEOK)
        { /* unable to create the link */ }

    if(! MLSetYieldFunction(link, (MLYieldFunctionObject)AppYieldFunction))
        { /* unable to set the yield function for link */ }

    /* ... */

    MLClose(link);
    MLDeinitialize(env);
    return 0;
}