swprintf declaration mismatch

Question

I use MinGW g++ compiler on Windows (gcc version 4.8.1) and I am confused with swprintf declaration

According to this reference it should be

int swprintf (wchar_t* ws, size_t len, const wchar_t* format, ...);

However when I use

swprintf(my_ws, 32, L"hello");

I get error

initializing argument 2 of 'int swprintf(wchar_t*, const wchar_t*, ...)' [-fpermissive]

Looks like size_t len is not in the declaration. Is the reference wrong, did I miss something or is there some story behind that?

Answer 1

You are using a C library that is not compliant with the C99 Standard.

MinGW is a port of gcc that uses the Microsoft C runtime library.

Microsoft had its own version of swprintf with a different prototype before it was standardized into C99. It is a very old C library with a lot of C99 incompatibilities, for example I don't think its printf supports %zu for size_t ...

You should upgrade to a more recent version of MinGW if they use a more recent runtime. If not, you are going to have to use the old prototype, and live with these obsolete APIs.