warning: ‘/name0’ directive output may be truncated writing 10 bytes into a region of size between 1 and 4096 [-Wformat-truncation=]

Question

#DEFINE LENGTH 4096

warning: ‘/name0’ directive output may be truncated writing 10 bytes into a region 
of size between 1 and 4096 [-Wformat-truncation=]
 snprintf(head_list->cname, LENGTH, "%s/name0", cpath);
                                       ^~~~~~~~~~

gcc is throwing this warning. How to fix this without using -Wformat-truncation= option?

cpath is a character with 4096 size

And if `head_list->cname` is a `char[10]`, then there is not enough space in the destination, hence `gcc` warns you about it. — Pablo, Feb 07 '22 at 03:40
Increate `LENGTH` so that `cpath` concatenated with `/name0` fits n `head_list->cname` — Ted Lyngmo, Feb 07 '22 at 03:40
it is a pointer to a structure (struct details *head_list) and cname is a character member — qwerty, Feb 07 '22 at 03:43
Does https://stackoverflow.com/questions/51534284/how-to-circumvent-format-truncation-warning-in-gcc answer your question? — KamilCuk, Mar 26 '22 at 11:40

score 1 · Answer 1 · answered Mar 26 '22 at 11:35

As cpath can be maximum 4096 characters long, appending /name0 to the end of it inherently create a string that can be longer than 4096 characters and can't fit into head_list->cname

If you're sure that cpath can't be longer than 4090 characters then tell gcc to turn off warning for that specific line

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wformat-truncation"
snprintf(head_list->cname, LENGTH, "%s/name0", cpath);
assert(strlen(cpath) <= 4090);
#pragma GCC diagnostic pop

warning: ‘/name0’ directive output may be truncated writing 10 bytes into a region of size between 1 and 4096 [-Wformat-truncation=]

1 Answers1