C语言：getopt_long()函数的作用
Linux系统下，需要大量的命令行选项，如果自己手动解析他们的话实在是有违软件复用的思想，不过还好，GNU C library留给我们一个解析命令行的接口(X/Open规范)，好好使用它可以使你的程序改观不少。使用getopt_long()需要引入头文件：#include<getopt.h>
现在我们使用一个例子来说明它的使用。
一个应用程序需要如下的短选项和长选项
短选项 长选项 作用
-h --help 输出程序命令行参数说明然后退出
-o filename--output filename给定输出文件名
-v --version 显示程序当前版本后退出
为了使用getopt_long()函数，我们需要先确定两个结构：
1.一个字符串，包括所需要的短选项字符，如果选项后有参数，字符后加一个":"符号。本例中，这个字符串应该为"ho:v"。(因为-o后面有参数filename,所以字符后面需要加":")。
2. 一个包含长选项字符串的结构体数组，每一个结构体包含4个域，第一个域为长选项字符串，第二个域是一个标识，只能为0或1，分别代表没有选项或有选项。第三个域永远为NULL。第四个选项域为对应的短选项字符串。结构体数组的最后一个元素全部位NULL和0，标识结束。在本例中，它应为以下的样子：
const struct option long_options[] = {
{"help", 0, NULL, 'h'},
{"output", 1, NULL, 'o'},
{"version", 0, NULL, 'v'},
{NULL, 0, NULL, 0}
};
调用时需要把main的两个参数argc和argv以及上述两个数据结构传给getopt_long()函数。
#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.
*/
program_name = argv;
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);
}
/**//* The main program goes here. */
return 0;
}
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