print and scan a string c

Question

I wanted to scan and print a string in C using Visual Studio.

#include <stdio.h>

main() {
    char name[20];
    printf("Name: ");
    scanf_s("%s", name);
    printf("%s", name);
}

After I did this, it doesn't print the name. What could it be?

do you enter a name at command promt ?.. as by looking at the code, everything seems good — Ankit
– Ankit, Commented Apr 14, 2015 at 14:12
Yes, if I type my name, it doesn't write anything as output. — TheWitcher
– TheWitcher, Commented Apr 14, 2015 at 14:13
Does Visual Studio give a warning about scanf_s("%s", name);? What version are you using? — chux
– chux, Commented Apr 14, 2015 at 16:08

Community · Accepted Answer · 2020-06-20 09:12:55Z

Quoting from the documentation of scanf_s,

Remarks:

[...]

Unlike scanf and wscanf, scanf_s and wscanf_s require the buffer size to be specified for all input parameters of type c, C, s, S, or string control sets that are enclosed in []. The buffer size in characters is passed as an additional parameter immediately following the pointer to the buffer or variable.

So, the scanf_s

scanf_s("%s", &name);

is wrong because you did not pass a third argument denoting the size of the buffer. Also, &name evaluates to a pointer of type char(*)[20] which is different from what %s in the scanf_s expected(char*).

Fix the problems by using a third argument denoting the size of the buffer using sizeof or _countof and using name instead of &name:

scanf_s("%s", name, sizeof(name));

or

scanf_s("%s", name, _countof(name));

name is the name of an array and the name of an array "decays" to a pointer to its first element which is of type char*, just what %s in the scanf_s expected.

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