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When I use visual studio, it says "scanf is unsafe, try using scanf_s". But if I use scanf_s in gcc or other compilers, it doesn't work. Does scanf_s works only on visual studio? If so, why? The visual studio website says "scanf is unsafe". If it is unsafe, then why others still uses it?

Muhammad Tawhidul Islam
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1 Answers1

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As mentioned here

scanf_s is Microsoft-specific. Header is stdio.h but not in GCC.

As documented here

When reading a string with scanf, always specify a width for the %s format (for example, "%32s" instead of "%s"); otherwise, improperly formatted input can easily cause a buffer overrun.
Alternately, consider using scanf_s, _scanf_s_l, wscanf_s, _wscanf_s_l or fgets.

See more at "Why didn't gcc implement _s functions?"

pmg adds in the comments that scanf_s() is Standard C11 (optional).
That means that activating c11 with gcc might be enough.

However Shawn adds:

IIRC, Microsoft's version doesn't follow the standard.
Plus no other major C library vendor has bothered to implement Annex K, so it might as well be MS specific for all intents and purposes.

pmg confirms:

My gcc (version 6.3.0) does not recognize scanf_s() with gcc -std=c11 -pedantic ...

VonC
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  • `scanf_s()` is Standard [C11 (optional)](http://port70.net/~nsz/c/c11/n1570.html#K.3.5.3.2) – pmg Jun 01 '19 at 07:26
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    @pmg IIRC, Microsoft's version doesn't follow the standard. Plus no other major C library vendor has bothered to implement Annex K, so it might as well be MS specific for all intents and purposes. – Shawn Jun 01 '19 at 07:29
  • @pmg So activating c11 with gcc would be enough? (https://stackoverflow.com/questions/16256586/how-to-enable-c11-on-later-versions-of-gcc) – VonC Jun 01 '19 at 07:29
  • My gcc (version 6.3.0) does not recognize `scanf_s()` with `gcc -std=c11 -pedantic ...` – pmg Jun 01 '19 at 07:35