homework/scanfprob.c

   1 /*
   2  * Compile with:
   3  * gcc scanfprob.c -o scanfprob -Wall -W -Wextra -ansi -pedantic
   4  */
   5
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8
   9 int main(void)
  10 {
  11     char buffer[100];
  12     int a, rv;
  13
  14     /*
  15      * When scanf is attempting to convert numbers, any non-numeric characters
  16      * it encounters terminate the conversion and are left in the input stream.
  17      * Therefore, unexpected non-numeric input ``jams'' scanf again and again.
  18      * E.g. Try to type a char and see what happens with the following code:
  19      *
  20      * do {
  21      *     printf("Input: ");
  22      *     scanf("%d", &a);
  23      * } while (a != -1);
  24      *
  25      * See also: http://c-faq.com/stdio/scanfjam.html
  26      */
  27
  28     /* First approach: check against the return value of scanf(3)  */
  29     do {
  30         printf("Input: ");
  31         rv = scanf("%d", &a);
  32         if (rv == 0)
  33             scanf("%[^\n]");
  34     } while (a != -1);
  35
  36     /* Second approach: combine fgets(3) with sscanf(3)  */
  37     getchar();    /* Trim '\n' from previous */
  38     do {
  39         printf("Input: ");
  40         fgets(buffer, sizeof buffer, stdin);
  41         rv = sscanf(buffer, "%d", &a);
  42     } while (rv == 0 || a != -1);
  43
  44     return EXIT_SUCCESS;
  45 }