将scanf与char数组及其大小一起使用

Question

I am learning C with Deitel's and Deitel's C programming book. Most of the times, when they use the scanf fucntion, for a char name[20]; , they usually write: scanf("%19s", name); , in order to avoid buffer overflow.

But what can we do if the length of the array is a symbolic constant, say #define LENGTH 20 . Obviously, using scanf("%LENGTHs, name); or even scanf("%"LENGTH"s", name); doesn't really help.

My problem also applies to the fscanf function, when we have to do with a stream different than stdin .

Answer 1

Like this:

#include <stdio.h>

#define STR_(x) #x
#define STR(x) STR_(x)

#define LENGTH 20

int main(void){
    char name[LENGTH+1];

    scanf("%" STR(LENGTH) "s", name);
    puts(name);
    return 0;
}

See Stringification for more information on this.

Answer 2

Is better to use fgets(buffer, sizeof(buffer), stdin)

But If you want to use scanf() you can create the format at runtime or
re-define LENGTH to be a string;

#define LENGTH "20"
scanf(" %" LENGTH "[^\n]", name);

Edit:

try this:

#include <stdio.h>
#define LENGTH "10"

int main(void) {
    char name[20];
    scanf(" %" LENGTH "[^\n]", name);
    puts(name);
    return 0;
}

Input: abcdefghijklmnopqrstuvxyz
Output: abcdefghij

All the best.