Question

How can I print a non-null-terminated string using printf, assuming that I know the length of the string at runtime?

Answer 1

printf("%.*s", length, string);

Use together with other args:

printf("integer=%d, string=%.*s, number=%f", integer, length, string, number);
//                         ^^^^                       ^^^^^^^^^^^^^^

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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.