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carraysprintfmemset

do snprintf() internally call memset() or similar?

I'm cognizant of using snprintf() in lieu of sprintf() for safety. However, I always do memset() on buffer used by snprintf(). I saw some codes using the function without memset(). And, it works as expected. I mean there is no overwriting on the buffer. Let me exemplify,

char str[100];
snprintf(str, sizeof(str), "stackoverflow %zu", sizeof(str));
fprintf(stderr, "%s\n", str);

snprintf(str, sizeof(str), "soner");
fprintf(stderr, "%s\n", str);

Until now, I thought that the code would print soneroverflow 100 that's why I used memset(). Nevertheless, it prints soner. How is it done underhood? By the way, same thing is applied for sprintf().

Solution

  • From snprintf:

    A terminating null character is automatically appended after the content written.

    If you were to inspect the buffer, you would find 

    { 's', 'o', 'n', 'e', 'r', '\0', 'v', 'e', 'r', /* ... */ }