A frequently-occurring idiom in C code is the "out parameter". If a C function returns more than one value, the caller passes pointers of the correct type, and the C function writes its return values to those locations.

with-out-parameters ( c-types quot -- values... )

The idiom is commonly used for passing back an error message if the function calls fails. For example, if a function is declared in the following way:

Then it could return 1 on error and 0 otherwise. A correct way to call it would be:

which would put the function's return value and error string on the stack.