Read an Integer from the User, Part 2

by Dave Sinkula on Aug 10th, 2005

Some issues, such as leading whitespace and trailing characters that cannot be part of a number, were not handled in Read an Integer from the User, Part 1. Here such issues receive lip service.

C Code Snippet (Toggle Plain Text)

#include <stdio.h>
#include <ctype.h>
 
int mygeti(int *result)
{
        char c, buff [ 13 ]; /* signed 32-bit value, extra room for '\n' and '\0' */
        return fgets(buff, sizeof buff, stdin) && !isspace(*buff) &&
        sscanf(buff, "%d%c", result, &c) == 2 && (c == '\n' || c == '\0');
}
 
int main(void)
{
        int value;
        do {
                fputs("Enter an integer: ", stdout);
                fflush(stdout);
        } while ( !mygeti(&value) );
        printf("value = %d\n", value);
        return 0;
}
 
/* my output
Enter an integer: one
Enter an integer:
Enter an integer: f123
Enter an integer: 123f
Enter an integer:  123
Enter an integer: 123
Enter an integer: 1.23
Enter an integer: -42
value = -42
*/
 
/* note: this line in the above has a space character following the 123
Enter an integer: 123
*/