Getopt和Optarg

Question

Hi I am working on a Program in a book. The Program is working almost as it is supposed to, except for one mistake. Every time I try to use the "-l" case I get a Segmentation Fault. Any Ideas?

#include <stdio.h> 
#include <unistd.h>

int main(int argc, char *argv[])
{
    char *lieferung = "";
    int knusprig = 0;
    int zahl = 0;
    char ch;

while ((ch = getopt(argc, argv, "l : k")) != EOF){
    switch (ch) {
        case 'l':
            lieferung = optarg;
            break;
        case 'k':
            knusprig = 1;
            break;
        default:
            fprintf(stderr, "Unbekannte Option: '%s'\n", optarg);
            return 1;
    }
}
argc -= optind;
argv += optind;

if (knusprig)
    puts("Knuspriger Rand.");
if (lieferung[0])
    printf("Zu liefern: %s.\n", lieferung);

puts("Zutaten:");
for (zahl = 0; zahl < argc; zahl++)
    puts(argv[zahl]);
return 0;
}

Thanks in advance.

Answer 1

The third argument get getopt shouldn't contain any spaces. Because there are spaces, it reads this argument as "-l takes no argument, -(space) takes an argument, -(space) takes no argument, and -k takes no argument.

Since getopt doesn't expect -l to pass an argument, optarg is set to NULL, which you then subsequently assign to lieferung . You then dereference that variable, resulting in the segfault.

Git rid of the spaces in the format string:

while ((ch = getopt(argc, argv, "l:k")) != EOF){

Answer 2

I think the format is incorrect. Replace "l : k" with "l:k".