Question

I have seen a function whose prototype is:

int myfunc(void** ppt) 

This function is called in a C file as a = myfunc(mystruct **var1);

where mystruct is typedef for one of structure we have.

This works without any compilation errors in MSVC6.0, But when I compile it with some other C compiler, it gives an error at the place where this function is called with error message:

Argument of type mystruct ** is incompatible with parameter of type void **

The argument of myfunc() is kept as void** because it seems to be a generic malloc kind of function to be called with various structure variable types for memory allocation

1. Is there any type such as void ** allowed in C standard/any C compilers?
2. How do I fix this? [I tried casting the function call argument to mystruct**, but it didn’t work]

-AD

Answer 1

void** is valid but, based on your error message, you probably have to explicitly cast the argument as follows:

mystruct **var1; x = myfunc ((void**) var1); 

That’s because the myfunc function is expecting the void** type. While void* can be implicitly cast to any other pointer, that is not so for the double pointer – you need to explicitly cast it.