C-strcmp无法与scanf（）一起使用

Question

I am trying to use scanf() with strcmp. However, it doesn't work. I've included the right header files. I've tried out gets(). It works but I don't want to be vulnerable of a buffer overflow attack.

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main() {
    char a[100] = "Hello World!";
    char b[100];

    scanf("%s", &b);

    if(strcmp(a, b) == 0) {
        printf("This should work!\n");
    }
}

I compile the program. Then, type Hello World! into the program. It won't show the message. Also, why does strcmp() show me all kinds of return values?

Please help.

Answer 1

Reading the manual on scanf -- you will see that it stops scanning a %s at the first whitespace found

scanf("%s", b);

of Hello World

will give you Hello but not Wolrd

Also note that scanf is equally vulnerable to buffer overflow, as you are still not limiting the size of the input in %s -- to limit the input you should probably try to do %99s making sure that you are not reading more than your 100 byte buffer still leavng space for your null termination.

As per this question you need something like

scanf("%[^\n]",str)

to read everything up to the newline, and combining that with a length restrction, you would need something like

scanf("%99[^\n]",str)