#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
int main(int argc, char *argv[]) {
    char* listen_arg = NULL;

    const struct option long_options[] = {
        {"listen", required_argument, NULL, 1000},
        {NULL, 0, NULL, 0}
    };

    int opt;
    int option_index;

    while ((opt = getopt_long(argc, argv, "", long_options, &option_index)) != -1) {
        switch (opt) {
            case 1000:
                listen_arg = optarg;
                printf("listen_arg is %s\n",listen_arg);
                break;
           case '?':
                fprintf(stderr, "Unknown option: %s\n", argv[optind - 1]);
                exit(EXIT_FAILURE);
        }
    }

    return 0;
}

./a.out --listen=1234和  ./a.out --lis=1234都会打印listen_arg is 1234。
为什么会这样？ 为什么不是精确匹配listen参数的
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