C program strings

Question

I run the following c program

char str[80] = "String";
printf("hello %s\n", str);
scanf("%s", str);
printf("%s\n", str);
scanf("%[ABCDEF]", str);
printf("hello %s\n", str);

return 0;

For some reason on line 5 when it is suppose to input from Pattern %[ABCDEF], the console simply prints previous string (input from line 3). Why is that so?

your str declaration does not make sense. you can't update literal values like that. — OldProgrammer
– OldProgrammer, Commented May 10, 2021 at 17:34
You do know that scanf does return a value - perhaps worth checking — Ed Heal
– Ed Heal, Commented May 10, 2021 at 17:57
@OldProgrammer i was simply trying to see how the c program is behaving because i'm learing. So yeah, i got the answer from August Karlstorm — rakkshit
– rakkshit, Commented May 11, 2021 at 11:28
@DavidSchwartz if i correct it as scanf(" %[ABCDEF]", str); now string takes only characters specified between [] — rakkshit
– rakkshit, Commented May 11, 2021 at 11:31

August Karlstrom · Accepted Answer · 2021-05-10 18:08:30Z

4

Thats because the first scanf call doesn't read the newline character and the second call to scanf simply reads that newline character. To avoid this start the format string with a space like this:

#include <stdio.h>

int main(void)
{
    char str[80] = "String";

    printf("hello %s\n", str);
    scanf("%s", str);
    printf("%s\n", str);
    scanf(" %[ABCDEF]", str);
    printf("hello %s\n", str);

    return 0;
}

However, you also need to make sure that str doesn't overflow if the user inputs a string longer than 79 characters.

edited May 10, 2021 at 18:08

answered May 10, 2021 at 17:55

August Karlstrom

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