using getopt with gdb

问题:

have just incorporated getopt into my main() func

getopt sets the global variable optarg for each call

stepping through main() with gdb, after getopt() call optarg is always NULL (e.g. (gdb) p optarg) yet printf("%s\n", optarg) outputs the cmd line arg as expected

whats going on? why are the two not the same?

Is this an isue with gdb and how it trys to inspect globals or is something else going on?

回答1:

Probably related: Bug 13800 - gdb does not print right values of getopt-related values

Also notice ie:

(gdb) n
opt: 111, arg, 
0x804a040
0x804a034
0x804a020
0x804a030

(gdb) printf "%p\n%p\n%p\n%p\n", &optarg, &opterr, &optind, &optopt
0x2ae760
0x2ab0f4
0x2ab0f8
0x2ab0f0

Where:

(gdb) l
6   int main(int argc, char *argv[])
7   {
8       int c;
9       while ((c = getopt(argc, argv, ":abf:o:")) != -1) {
10          printf("opt: %d, %s, \n"
11              "%p\n%p\n%p\n%p\n",
12              c, optarg,
13              &optarg, &opterr, &optind, &optopt);