C++ – Clean Code for Printing size_t with printf

I have some C++ code that prints a size_t:

size_t a;
printf("%lu", a);

I'd like this to compile without warnings on both 32- and 64-bit architectures.

If this were C99, I could use printf("%z", a);. But AFAICT %z doesn't exist in any standard C++ dialect. So instead, I have to do

printf("%lu", (unsigned long) a);

which is really ugly.

If there's no facility for printing size_ts built into the language, I wonder if it's possible to write a printf wrapper or somesuch such that will insert the appropriate casts on size_ts so as to eliminate spurious compiler warnings while still maintaining the good ones.

Any ideas?

Edit To clarify why I'm using printf: I have a relatively large code base that I'm cleaning up. It uses printf wrappers to do things like "write a warning, log it to a file, and possibly exit the code with an error". I might be able to muster up enough C++-foo to do this with a cout wrapper, but I'd rather not change every warn() call in the program just to get rid of some compiler warnings.