warning: '__builtin_snprintf' output may be truncated before the last format character [-Wformat-truncation=]

Question

warning: ‘__builtin_snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
  "%s", evspan->text);
     ^

len = strlen(evspan->text);
evspan->ent->content = malloc(len+1);

snprintf(evspan->ent->content, len,
"%s", evspan->text);

I saw this warning on gcc 8. How do I prevent this without using -Wformat-truncation option?

Answer 1

The second argument to snprintf is the length of the buffer, not the maximum string length.

The call should be:

snprintf(evspan->ent->content, len + 1, "%s", evspan->text);

This matches the length passed to malloc.

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The comments given on snprintf not being the best choice do apply, if your full code is as simple as what's shown here.