I'm personally fond of filling an error buffer, but a bit more explicitly than just an int. typedef struct APIError { int code; char *descr

I'm personally fond of filling an error buffer, but a bit more explicitly than just an int. typedef struct APIError { int code; char *description; }; /** * Returns NULL and fills the error parameter if creation was unsuccessful. */ Something APICreateSomething(bool param1, int param2, APIError *error); So common execution would be: APIError error; Something something = APICreateSomething(true, 3, &error); if (error) { // handle error... } And if the user passed in NULL for the error parameter, then that's their problem, and they won't get error information.