vsnprintf, _vsnprintf, vsnwprintf, _vsnwprintf
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Header File
stdio.h
Category
Memory and String Manipulation Routines
Prototype
int _vsnprintf(char* buffer, size_t nsize, const char* format, va_list param);
int _vsnwprintf(wchar_t* buffer, size_t nsize, const wchar_t* format, va_list param);
Description
Sends formatted output to a buffer of maximum length specified by nsize.
If the number of bytes to output is:
- < nsize, then all of the characters have been written, including the terminating '\0' character.
- == nsize, then nsize characters are written, with no terminating '\0' character.
- > nsize, then only nsize characters are written, with no terminating '\0' character.
If nsize is 0, then the string will not be written to (and may be NULL).
Return Value
The number of bytes output, or, if nsize is 0, the number of bytes needed, not including the terminating '\0' character.
Portability
| POSIX | Win32 | ANSI C | ANSI C++ |
|---|---|---|---|
|
+ |
+ |
+ |
Example
#include <stdio.h>
#include <wtypes.h>
void Vprint_test(char *format, ...)
{
int n_byte = 0;
char buff[30];
buff[0]=0;
va_list param; //the list of parameters
va_start(param, format);
n_byte = vsnprintf( buff, sizeof(buff) - 1, format, param);
//Compare the buffer's length with the byte written to see whether the buffer was big enough
if (n_byte<sizeof(buff)) {
printf("all characters were written:(%d bytes)\n buff: %s\n", n_byte, buff);
} else
{
if (n_byte==sizeof(buff)) {
printf("%d characters were written(with no terminating character):(%d bytes)\n buff: %s\n", sizeof(buff),n_byte, buff);
}else
printf("only %d characters were written(with no terminating character):(%d bytes)\n buff: %s\n", sizeof(buff),n_byte, buff);
}
}
int main() {
Vprint_test("%s %d %f", "Hello", 123, 23.45);
return 0;
}