Why does ] not displayed in C?

Question

This is my code snippet in C:

      char *str = NULL;
      int len = -1;

      // Get length
      len = snprintf(NULL, 0, "[%d]", 2);

      // Allocate str
      str = (char *)malloc(len + 1);

      // Assign str
      snprintf(str, len, "[%d]", 2);

      assert(len == 3);

      // Display str
      puts(str);

I expect this should display [2]. And len here is 3.

But running this code displays only [2

Why is this so?

Please [don't cast the return value of `malloc()` in C](http://stackoverflow.com/a/605858/28169). — unwind, Apr 02 '13 at 09:13

score 11 · Accepted Answer · answered Apr 02 '13 at 09:08

11

The length of the buffer is len+1, but you only pass len to snprintf, try this:

snprintf(str, len + 1, "[%d]", 2);

from cplusplus.com:

If the resulting string would be longer than n-1 characters, the remaining characters are discarded and not stored, but counted for the value returned by the function.

A terminating null character is automatically appended after the content.

answered Apr 02 '13 at 09:08

MByD

135,866
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Yes. This answer is correct and will be accepted after 6 minutes. "You can accept an answer in 6 minutes". – Neigyl R. Noval Apr 02 '13 at 09:14

score 0 · Answer 2 · answered Apr 02 '13 at 09:15

0

The functions snprintf() write at most len bytes (including the terminating null byte ('\0')) to str.

len equal to 3 (the first call), so snprintf will write only 3 char: '[', '2' and '\0'.

answered Apr 02 '13 at 09:15

Bechir

987
10
26

Why does ] not displayed in C?

2 Answers2