snprintf and Visual Studio 2010
I'm unfortunate enough to be stuck using VS 2010 for a project, and noticed the following code still doesn't build using the non-standards compliant compiler:
#include <stdio.h>
#include <stdlib.h>
int main (void)
{
char buffer[512];
snprintf(buffer, sizeof(buffer), "SomeString");
return 0;
}
(fails compilation with the error: C3861: 'snprintf': identifier not found)
I remember this being the case way back with VS 2005 and am shocked to see it still hasn't been fixed.
Does any one know if Microsoft has any plans to move their standard C libraries into the year 2010?
Short story: Microsoft has finally implemented snprintf in Visual Studio 2015. On earlier versions you can simulate it as below.
Long version:
Here is the expected behavior for snprintf:
int snprintf( char* buffer, std::size_t buf_size, const char* format, ... );
Writes at most buf_size - 1 characters to a buffer. The resulting character string will be terminated with a null character, unless buf_size is zero. If buf_size is zero, nothing is written and buffer may be a null pointer. The return value is the number of characters that would have been written assuming unlimited buf_size , not counting the terminating null character.
Releases prior to Visual Studio 2015 didn't have a conformant implementation. There are instead non-standard extensions such as _snprintf() (which doesn't write null-terminator on overflow) and _snprintf_s() (which can enforce null-termination, but returns -1 on overflow instead of the number of characters that would have been written).
Suggested fallback for VS 2005 and up:
#if defined(_MSC_VER) && _MSC_VER < 1900
#define snprintf c99_snprintf
#define vsnprintf c99_vsnprintf
__inline int c99_vsnprintf(char *outBuf, size_t size, const char *format, va_list ap)
{
int count = -1;
if (size != 0)
count = _vsnprintf_s(outBuf, size, _TRUNCATE, format, ap);
if (count == -1)
count = _vscprintf(format, ap);
return count;
}
__inline int c99_snprintf(char *outBuf, size_t size, const char *format, ...)
{
int count;
va_list ap;
va_start(ap, format);
count = c99_vsnprintf(outBuf, size, format, ap);
va_end(ap);
return count;
}
#endif
snprintf is not part of C89. It's standard only in C99. Microsoft has no plan supporting C99.
(But it's also standard in C++0x...!)
See other answers below for a workaround.
如果你不需要返回值，你也可以将snprintf定义为_snprintf_s
#define snprintf(buf,len, format,...) _snprintf_s(buf, len,len, format, __VA_ARGS__)