[anonova]

I was looking for a small image processing library (as opposed to libMagickWand) and came across libvips [1]. I found it absolutely bizarre that the public API in a C library was full of variadic functions to support optional arguments. The last argument to most function calls is required to be NULL to denote the end of the argument list, e.g., https://libvips.github.io/libvips/API/current/using-from-c.h... (vips_image_new_from_file, vips_invert, etc.).

[1]: https://libvips.github.io/libvips/

[zlynx]

A fun one relating to 64-bit and NULL in varargs:

If your system defines NULL as 0, which is legal in C++, then NULL in the vararg list only pushes an int-sized (4 bytes) zero, and the vararg reader pulls a pointer-sized (8 bytes) value, which may or may NOT equal zero because of the 4 extra bytes...

[Avery3R]

If using modern c++ you should use nullptr instead

[liuliu]

Yeah, that is unfortunate. Even if you want to do that (in C, the correct way, of course, is to name them differently), should use macro to select correct function prototype to dispatch to, that still enables type checking and avoid the variadic function non-sense. Variadic function is pure evil (seriously, who can remember these random rules that in variadic function, a char will be promoted to int and a float will be promoted to double ...)