命令行参数的分析

1.getopt

 #include <unistd.h>

 int getopt(int argc, char * const argv[],
            const char *optstring);

 extern char *optarg;
 extern int optind, opterr, optopt;

optarg 如果一个选项带了参数，当解析到这个选项的时候，这个全局变量会自动指向这个参数
optind 记录读到了哪个下标

RETURN VALUE
       If  an option was successfully found, 
then getopt() returns the option character.
       If all command-line options have been  parsed, 
then  getopt()  returns  -1.   
        If getopt()  encounters  an  option character that 
was not in optstring, then '?' is returned

If the first character  of  optstring  is  '-',  then  each 
nonoption  argv-element  is  handled as if it were the argument of
 an option with character code 1.  
 (This is used by programs that were written to expect  options and 
  other  argv-elements  in  any  order and that care about the 
  ordering of the  two.)

如果格式的第一个字符是’-'的话，那么里面就包含一个非选项，匹配到了 会返回1

一个Demo

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <string.h>

#define MAXSIZE 1024


int main(int argc, char **argv)
{
	//这个文件描述符是记录向终端写入还是文件写入
	FILE *fp = stdout;
	time_t Int64Time;
	struct tm *pTime;
	//存储时间
	char TimeBuf[MAXSIZE];
	//存储转化格式
	char Format[MAXSIZE];
	//存储返回值
	int res;
	
	Format[0] = '\0';
	
	time(&Int64Time);
	pTime = localtime(&Int64Time);
	
	
	while(1)
	{
	        res = getopt(argc, argv, "-H:MSy:md");
	
	        if(res < 0)
	                break;
	
	        switch(res)
	        {
	                case 1:
	                        {
	                                fp = fopen(argv[optind-1] ,"w");
	                                if(NULL == fp)
	                                {
	                                        perror("fopen()");
	                                        fp = stdout;
	                                }
	                        }
	                        break;
	                case 'H':
	                        {
	                                if(0 == strcmp("24", optarg))
	                                        strncat(Format, "%H ", MAXSIZE);
	                                else if(0 == strcmp("12", optarg))
	                                        strncat(Format, "%I(%P) ", MAXSIZE);
	                                else
	                                        fprintf(stderr, "Illegal argv\n");
	                        }
	                        break;
	                case 'M':
	                        strncat(Format, "%M ", MAXSIZE);
	                        break;
	                case 'S':
	                        strncat(Format, "%S ", MAXSIZE);
	                        break;
	                case 'y':
	                        {
	                                if(0 == strcmp("2", optarg))
	                                        strncat(Format, "%y ", MAXSIZE);
	                                if(0 == strcmp("4", optarg))
	                                        strncat(Format, "%Y ", MAXSIZE);
	                                else
	                                        fprintf(stderr, "Illegal argv\n");
	                        }
	                        break;
	                case 'm':
	                        strncat(Format, "%m ", MAXSIZE);
	                        break;
	                case 'd':
	                        strncat(Format, "%d ", MAXSIZE);
	                        break;
	                default:
	                        break;
	        }
	         
	}
	
	//根据格式 来生成对应需要的时间格式
	strftime(TimeBuf, MAXSIZE, Format, pTime);
	//输出到fp
	fputs(TimeBuf, fp);
	puts("");
	
	//忘记加close了
	return 0;
}

-H:MSy:md

①- 这个杠代表要传入的参数里面有非选项，在这个例子中这个非选项是个文件，有非选项写入文件，没有写入终端
②：这个冒号代表他是有参数的选项 这个例子中的y和H 都带了参数