Linux系統下，需要大量的命令行選項，如果自己手動解析他們的話實在是有違軟件復用的思想，不過還好，GNU C library留給我們一個解析命令行的接口(X/Open規范)，好好使用它可以使你的程序改觀不少。
使用getopt_long()需要引入頭文件：#include<getopt.h>
現在我們使用一個例子來說明它的使用。
一個應用程序需要如下的短選項和長選項
短選項 長選項 作用
-h --help 輸出程序命令行參數說明然后退出
-o filename --output filename 給定輸出文件名
-v --version 顯示程序當前版本后退出
為了使用getopt_long()函數，我們需要先確定兩個結構：
1.一個字符串，包括所需要的短選項字符，如果選項后有參數，字符后加一個":"符號。本例中，這個字符串應該為"ho:v"。(因為-o后面有參數filename,所以字符后面需要加":")。
2. 一個包含長選項字符串的結構體數組，每一個結構體包含4個域，第一個域為長選項字符串，第二個域是一個標識，只能為0或1，分別代表沒有選項或有選項。第三個域永遠為NULL。第四個選項域為對應的短選項字符串。結構體數組的最后一個元素全部位NULL和0，標識結束。在本例中，它應為以下的樣子：
const struct option long_options[] = {
{"help", 0, NULL, 'h'},
{"output", 1, NULL, 'o'},
{"version", 0, NULL, 'v'},
{NULL, 0, NULL, 0}
};
調用時需要把main的兩個參數argc和argv以及上述兩個數據結構傳給getopt_long()函數。
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
/**//* The name of this program. */
const char* program_name;
/**//* Prints usage information for this program to STREAM (typically
stdout or stderr), and exit the program with EXIT_CODE. Does not
return. */
void print_usage(FILE* stream, int exit_code)
{
fprintf(stream, "Usage: %s options [ inputfile ]\n",
program_name);
fprintf(stream,
" -h --hlep Display this usage information.\n"
" -o --output filename Write output to file.\n"
" -v --verbose Print verbose message.\n");
exit (exit_code);
}
/**//* Main program entry point. ARGC contains number of argument list
elements; ARGV is an array of pointers to them. */
int main(int argc, char *argv[])
{
int next_option;
/**//* A string listing valid short options letters. */
const char* const short_options = "ho:v";
/**//* An array describing valid long options. */
const struct option long_options[] = {
{"help", 0, NULL, 'h'},
{"output", 1, NULL, 'o'},
{"verbose", 0, NULL, 'v'},
{NULL, 0, NULL, 0} /**//* Required at end of array. */
};
/**//* The name of the file to receive program output, or NULL for
* standard output.
*/
const char* output_filename = NULL;
/**//* Whether to display verbose messages. */
int verbose = 0;
/**//* Remember the name of the program, to incorporate in messages.
* The name is stored in argv[0].
*/
program_name = argv[0];
do {
next_option = getopt_long (argc, argv, short_options,
long_options, NULL);
switch (next_option)
{
case 'h': /**//* -h or --help */
/**//* User has requested usage information. Print it to
* standard output, and exit with exit code zero
* (normal termination).
*/
print_usage(stdout, 0);
case 'o': /**//* -o or --output */
/**//* This option takes an argument, the name of the
* output file.
*/
output_filename = optarg;
break;
case 'v': /**//* -v or --verbose */
verbose = 1;
break;
case '?': /**//* The user specified an invalid option. */
/**//* Print usage information to standard error, and exit
* with exit code one (indicating abnormal
* termination).
*/
print_usage(stderr, 1);
case -1: /**//* Done with options. */
break;
default: /**//* Something else: unexpected. */
abort();
}
}
while (next_option != -1);
/**//* Done with options. OPTINO points to first nonoption argument.
* FOr demonstration purposes, print them if the verbose option
* was specified.
*/
if (verbose)
{
int i;
for (i = optind; i < argc; ++i)
printf("Argument: %s\n", argv[i]);
}
/**//* The main program goes here. */
return 0;
}