Freetype 2，Building Visual Studio 2015

Question

Getting the following warning:

ttgload.c(1654): warning C4312: 'type cast': conversion from 'FT_UInt' to 'void *' of greater size

Which seems rather odd.

The line of code in question is this:

if ( FT_List_Find( &loader->composites,
                   (void*)(unsigned long)glyph_index ) )

and glyph_index is declared FT_UInt .

FT_UInt is typedef unsigned int so it is rather strange to convert an int to a void* .

Any ideas on how to deal with this warning?

Answer 1

FT_UInt is typedef unsigned int so it is rather strange to convert an int to a void*.

Actually it's not. It's perfectly fine and allowed to convert between integers and pointers. A particular application of this is "user parameters" to a function where you register integer or a pointer together with a function callback.

However the two-fold typecast (void*)(unsigned long) is a recipe for getting problems. It's not guaranteed that sizeof(unsigned ling) >= sizeof(void*) which may cause all kinds of problems (ie undefined behaviour) of pointers get truncated.

The proper types to use when someone wants an integer that also can hold a pointer are uintptr_t and intptr_t .

Any ideas on how to deal with this warning?

In this particular case it's likely not a cause of problems, because that pointer is going to be cast back to an FT_UInt. In the long run it would make sense to file an issue and change the prototype of FT_List_Find to accept a uintptr_t instead of a pointer; unfortunately this would also break a lot of existing programs.