Implicit declaration of function 'scan_s' [-Wimplicit-function-declaration]

Question

I've been looking at other questions and none of the solutions have worked so I'll ask my own question.

I'm working on a linux VM and having trouble compiling my code, here are my includes, the error received by the compiler and the code its referring to:

Error:

linux.c:156:11: warning: implicit declaration of function 'scan_s' [-Wimplicit-function-declaration]

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include "ctype.h"

scanf_s("%[^\n]s", filename, maxFilename);

Possible duplicate of [Header for scanf\_s function](http://stackoverflow.com/questions/18836661/header-for-scanf-s-function) — Zbynek Vyskovsky - kvr000, Jan 18 '16 at 12:34
The [`scanf_s`](http://en.cppreference.com/w/c/io/fscanf) function is pretty new, it was introduced in the C11 standard, and older Linux installations might not have it yet. — Some programmer dude, Jan 18 '16 at 12:35
Please show the **exact code**, or a [mcve]. The error suggests that you used `scan_s` instead of `scanf_s`. — Spikatrix, Jan 18 '16 at 13:40

Chris Dodd · Answer 1 · 2016-01-18T17:33:17.167

scanf_s is part of the bounds-checking extension that your compiler may not support. Use #ifdef __STDC_LIB_EXT1__ to see if your library/implementation supports it -- if not, fall back to using something like

char fmt[16];
sprintf(fmt, "%%%d[^\n]", maxFilename);
scanf(fmt, maxFilename, filename);

or

fgets(filename, maxFilename, stdin);
if (char *p = strchr(filename, '\n')) *p = '\0';

instead.

Note that the s in the format string of your example is non-sensical and will not match anything (any s will be absorbed by the %[^\n] as it is not a newline.

As far as I know, only Microsoft compilers support this extension.

Implicit declaration of function 'scan_s' [-Wimplicit-function-declaration]

1 Answers1