Calling a C function with a varargs argument dynamically

Question

I am programming in C against a third party library (in HP/Mercury Loadrunner) that allows a varargs-style variable size argument list for one of it\'s functions. I want to

Answer 1

Variable length arguments are basically just a pointer to a bunch of packed data that is passed to the required function. It is the responsibility of the called function to interpret this packed data.

The architecture safe way to do this is to use the va_list macros (that n-alexander mentioned), otherwise you may run into issues with how various data types are padded in memory.

The proper way to design varargs functions is to actually have two versions, one that accepts the '...', which in turn extracts the va_list and passes it to a function that takes a va_list. This way you can dynamically construct the arguments if you need to and can instead call the va_list version of the function.

Most standard IO functions have varargs versions: vprintf for printf, vsprintf for sprintf... you get the idea. See if your library implements a function named "vweb_submit_data" or something to that effect. If they don't, email them and tell them to fix their library.

3000 lines of the same thing (even if it is preprocessor induced) makes me cringe