getopt_long可以用来解析命令行参数,也可以进行参数解析。例如
#include <stdio.h> /* for printf */ #include <stdlib.h> /* for exit */ #include <getopt.h> static int verbose_flag; int parse(int argc, char **argv) { int c; int digit_optind = 0; while (1) { int this_option_optind = optind ? optind : 1; int option_index = 0; static struct option long_options[] = { {"verbose", no_argument, &verbose_flag, 1}, {"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 } }; c = getopt_long(argc, argv, "abc:d:012", long_options, &option_index); if (c == -1) break; switch (c) { case 0: printf("option %s", long_options[option_index].name); if (optarg) printf(" with arg %s", optarg); printf("\n"); break; case '0': case '1': case '2': if (digit_optind != 0 && digit_optind != this_option_optind) printf("digits occur in two different argv-elements.\n"); digit_optind = this_option_optind; printf("option %c\n", c); break; case 'a': printf("option a\n"); break; case 'b': printf("option b\n"); break; case 'c': printf("option c with value '%s'\n", optarg); break; case 'd': printf("option d with value '%s'\n", optarg); break; case '?': break; default: printf("?? getopt returned character code 0%o ??\n", c); } } if (optind < argc) { printf("non-option ARGV-elements: "); while (optind < argc) printf("%s ", argv[optind++]); printf("\n"); } if (verbose_flag) printf ("verbose flag is set\n"); return 0; } void main() { char *argv[6]={0}; int argc = 6; argv[0] = "prog1"; argv[1] = "--add"; argv[2] = "AA"; argv[3] = "-d"; argv[4] = "BB"; argv[5] = "--verbose"; parse(argc, argv); optind = 1; char *argv2[4]={0}; int argc2 = 4; argv2[0] = "prog2"; argv2[1] = "--file"; argv2[2] = "CC"; argv2[3] = "--verbose"; //argv2[3] = "--delete"; //argv2[4] = "DD"; parse(argc2, argv2); return ; }
getopt可以解析一个字母的命令行参数, “-d”, getopt_long则可以解析更长名称的命令行参数, 以”–“开头, 如例子中的”–file”.
参数比getopt多了两个, 函数原型如下:
#include <unistd.h> int getopt(int argc, char * const argv[], const char *optstring); extern char *optarg; extern int optind, opterr, optopt; #include <getopt.h> int getopt_long(int argc, char * const argv[], const char *optstring, const struct option *longopts, int *longindex); int getopt_long_only(int argc, char * const argv[], const char *optstring, const struct option *longopts, int *longindex);
另外注意函数依赖的定义, 编译时可以指定
getopt(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE
getopt_long(), getopt_long_only(): _GNU_SOURCE
getopt_long 参数结构体相对复杂一些
struct option { const char *name; int has_arg; int *flag; int val; };
static struct option long_options[] = { {"verbose", no_argument, &verbose_flag, 1}, {"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 } };
如果设置了flag不为null, 那么将val值复制给flag指针指向变量。
例子中是将verbose_flag设置为 1.
如果设置了flag为null, 那么val作为返回值, 这个返回值可以是设置为含义相同的短类型参数的标签,
例子中的c和create是相同的含义, 一个是长类型参数, 一个是短类型的参数。
另外还有个比较重要的全局变量:
extern char *optarg; extern int optind, opterr, optopt;
如果 getopt() 无法识别选项字符,它将向 stderr 打印一条错误消息,将该字符存储在 optopt 中,并返回“?”。调用程序可以通过将 opterr 设置为 0 来防止出现错误消息。
因为optind存储的下一个要解析的参数, 如果是getopt_long, 可以保留optind位置, 解析出错时显示
#include <stdio.h> /* for printf */ #include <stdlib.h> /* for exit */ #include <getopt.h> static int verbose_flag; int parse(int argc, char **argv) { ... case '?': printf("unkown option '%s'\n", argv[old_optnd]); break; default: printf("?? getopt returned character code 0%o ??\n", c); } old_optnd = optind; } ... } void main() { opterr = 0; char *argv[8]={0}; int argc = 8; argv[0] = "prog1"; argv[1] = "--add"; argv[2] = "AA"; argv[3] = "-d"; argv[4] = "BB"; argv[5] = "--verbose"; argv[6] = "--error"; argv[7] = "ddd"; parse(argc, argv); optind = 1; char *argv2[4]={0}; int argc2 = 4; argv2[0] = "prog2"; argv2[1] = "--file"; argv2[2] = "CC"; argv2[3] = "--verbose"; //argv2[3] = "--delete"; //argv2[4] = "DD"; parse(argc2, argv2); return ; }
如果不设置 opterr, 会有错误输出 prog1: unrecognized option ‘–error’
garlic@garlic:~/getoption$ ./test option add with arg AA option d with value 'BB' option verbose prog1: unrecognized option '--error' unkown option '--error' non-option ARGV-elements: ddd verbose flag is set option file with arg CC option verbose verbose flag is set
opterr设置为1 则没有相关输出。
解析完毕后记得要重新optind, 因为这个变量使用后不会重置。会出现 Segment Fault
参考及引用
https://www.gnu.org/software/libc/manual/html_node/Getopt-Long-Option-Example.html
https://linux.die.net/man/3/getopt_long
https://cplusplus.com/forum/unices/104742/ optind问题
图片from陳為
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