함수 vsnprintf()

#include <stdio.h> int snprintf(char *str, size_t size, const char *format, ...); #include <stdarg.h> int vsnprintf(char *str, size_t size, const char *format, va_list ap);   이 함수들을 사용하는 이유 = 주어진 size만큼만 str에 print하기 위함. 즉, buffer overflow를 막기 위함

 

// crt_vsnprintf.c
// compile by using: cl /W4 crt_vsnprintf.c
#include <stdio.h>
#include <stdarg.h> // for va_list, va_start
#include <string.h> // for memset

#define BUFFCOUNT (10)

void FormatOutput(char* formatstring, ...)
{
    int nSize = 0;
    char buff[BUFFCOUNT];
    memset(buff, 0, sizeof(buff));
    va_list args;
    va_start(args, formatstring);
    nSize = vsnprintf(buff, sizeof(buff), formatstring, args);
    printf("nSize: %d, buff: %s\n", nSize, buff);
    va_end(args);
}

int main() {
    FormatOutput("%s %s", "Hi", "there");   //  8 chars + null
    FormatOutput("%s %s", "Hi", "there!");  //  9 chars + null
    FormatOutput("%s %s", "Hi", "there!!"); // 10 chars + null
}
*********************************************************************
output:
nSize: 8, buff: Hi there
nSize: 9, buff: Hi there!
nSize: 10, buff: Hi there!