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cgnuglibcgetoptgetopt-long

Why does ommitting this one line from getopt_long() make a segfault?

After I compile using gcc -Wall getopt.c -o options and run a few examples, it seems to work at first glance. Purposely tripping it up makes it Segfault.

//straight from the man page
static struct option long_options[] = {
    {"add",     required_argument, 0,  0 },
    {"append",  no_argument,       0,  0 },
    {"delete",  required_argument, 0,  0 },
    {"verbose", no_argument,       0,  0 },
    {"create",  required_argument, 0, 'c'},
    {"file",    required_argument, 0,  0 },
    {0,         0,                 0,  0 } //<-- if i omit this line, it segfaults
};

Why does it cause a Segmentation Fault when I omit that one line?

or rather, asked in a different way

Why must I initialize the last set of struct option array members to null?

Solution

  • Easy. So the code processing the array knows when it's at the end. It's called a sentinel.