printf("%.*s", length, string);
Use together with other args:
printf("integer=%d, string=%.*s, number=%f", integer, length, string, number);
// ^^^^ ^^^^^^^^^^^^^^
In C you could specify the maximum length to output with the %.123s format. This means the output length is at most 123 chars. The 123 could be replaced by *, so that the length will be taken from the argument of printf instead of hard-coded.
Note that this assumes the string does not contain any interior null bytes (\0), as %.123s only constrains the maximum length not the exact length, and strings are still treated as null-terminated.
If you want to print a non-null-terminated string with interior null, you cannot use a single printf. Use fwrite instead:
fwrite(string, 1, length, stdout);
See @M.S.Dousti’s answer for detailed explanation.