C++, create a pthread for a function with a return type?

Question

Say I have the following function:

bool foo (int a); // This method declaration can not be changed.

How do I create a pthread for this? And how

Answer 1

As far as you're dealing only with bools (which are, in fact, integers) it's possible, however not recommended, to cast the function to a pthread function type, as a pointer is compatible with (some) integer types:

pthread_t pid;
pthread_create(&pid, NULL, (void *(*)(void *))foo, (void *)argument));

However, you'd better wrap your function into another, pthread-compatible one, then return a pointer to its return value (must be free()'d after use):

void *foo_wrapper(void *arg)
{
    int a = *(int *)arg;
    bool retval = foo(a);
    bool *ret = malloc(sizeof(bool));
    *ret = retval;
    return ret;
}

then use:

pthread_t pid;
pthread_create(&pid, NULL, foo_wrapper, &a);

With this method, in the future you'll be able to call a function with arbitrary return or argument types.