Question

I am porting a legacy C program to C++. However, the compiler is not happy and requires additional typecastings for C++. For example, I have this function…

 void foreach_element_in_patch(Patch *patch, void (*func)(), 
long arg1, long process_id);

In the original C Code, it is used like this…

 foreach_element_in_patch( patch, display_interactions_in_element, 
mode, process_id );

However, for C++ I need to typecast the second argument to stop the compiler from gernerating an error.

 foreach_element_in_patch( patch, (void (*)())display_interactions_in_element, 
mode, process_id );

The error generated by the compiler is the following…

invalid conversion from ‘void (*)(Patch*, long int, long int)’ to ‘void (*)()’

Now is there a way to ask the compiler not to generate errors for such things. I have tried prefixing this function with extern "C" but still the C++ compiler is not happy. My applications is loaded with such code and I do not have the time to adjust so much code.

Answer 1

The easiest thing to do is to change the function prototypes and headers to declare the correct type of function pointer. So for example, for

void foreach_element_in_patch(Patch *patch, void (*func)(), 
 long arg1, long process_id);

I just need to change it to

void foreach_element_in_patch(Patch *patch, void (*)(Patch*, long int, long int), 
 long arg1, long process_id);

Instead of making changes at every function call.