Is vsnprintf_s an appropriate replacement for deprecated vsnprintf?
c, printf, visual-studio-2010
Solution
Turns out this question is pretty much an exact duplicate of:
Calculating the size of an sprintf() buffer
Summary of the answer:
Use `_vscprintf` to figure out how big the buffer should be, then use `vsnprintf_s` to actually fill it.
Problem
In my code (strict C, not C++), I use vsnprintf this way: ``` char* buf = NULL; size_t sz; sz = vsnprintf( buf, 0, format, args); // Ask vsnprintf how big a buffer we need buf = (char*) malloc(sz + 1); vsnprintf( buf, sz, format, args); // Now actually fill the buffer /* Use buf in a dialog box... then: */ free(buf); ``` But MS Visual C++ (MSVS10) compiler warns: ``` warning C4996: 'vsnprintf': This function or variable may be unsafe. Consider using vsnprintf_s instead. ``` However, `vsnprintf_s` does not have the nifty feature that when you pass NULL for the buffer it will describe how much data it would have printed. Instead, it is documented to return -1. I feel I'm using `vsnprintf` in a safe manner by determining the necessary size, and that the recommended replacement, `vsnprintf_s` isn't the same at all. Am I missing a better / smarter way to use `vsnprintf_s`??