二、linux环境

1. argc and argv
   main函数原型
   int main(int argc, char* argv[])
   argc代表命令行参数的个数，argv保存命令行参数内容

     #include
     int main(int argc, char* argv[]){
         printf("program name:%s\n", argv[0]);
         for(int i = 1; i < argc ; i++){
             if(argv[i][0] == '-'){
                 printf("option:%s\n", argv[i] + 1);
             }else{
                 printf("argument:%s\n", argv[i]);
             }
     
         }
         return 0;
     }
   

2. 使用getopt处理命令行参数

   
   
   

   #include
   #include
   extern char *optarg;
   extern int opterr, optind, optopt;
   int main(int argc, char *argv[]){
       int opt;
       while((opt = getopt(argc, argv, "if:rs")) != -1){
           switch(opt){
               case 'i': 
               case 'r': 
               case 's': 
                   printf("option:%c\n", opt);
                   break;
               case 'f': 
                   printf("filename:%s\n", optarg);
               default: 
                   printf("unknown argument!\n");
                   break;
           }
       }
       for(;optind < argc; optind++){
           printf("argument:%s\n", argv[optind]);
       }
       return 0;
   }
   

   使用getopt_long处理长参数类型

   #include
   #include
   #include
   #define _GNU_SOURCE
   extern char* optarg;
   extern int optopt, optind, opterr;
   int main(int argc, char* argv[]){
       int opt;
       struct option options[] = {
           {"initialize", 0, NULL, 'i'},
           {"restart", 0, NULL, 'r'},
           {"stop", 0, NULL, 's'},
           {"file", 1, NULL, 'f'}
       };
       while((opt = getopt_long(argc, argv, "irsf:", options, NULL)) != -1){
           switch(opt){
               case 'i': 
               case 'r': 
               case 's': 
                   printf("option:%c\n", opt);
                   break;
               case 'f': 
                   printf("filename:%s\n", optarg);
                   break;
               default:
                   printf("unknown arguments!");
                   break;
           }
       }
       for(;optind < argc; optind++){
           printf("other argument:%s\n", argv[optind]);
       }
       return 0;
   }
   

3. 使用getenv与putenv获取并设置环境变量

   #include
   #include
   #include
   int main(int argc, char* argv[]){
       if(argc == 1 || argc > 3){
           fprintf(stderr, "invalid argument!");
           exit(1);
       }
       char *var = argv[1];
       char *value = getenv(var);
       if(value){
           printf("The environment variable %s has value %s\n", var, value);
       }else{
           printf("The environment variable %s has no value!\n", var);
       }
   
       if(argc == 3){
           value = argv[2];
           char *string = (char*)malloc(strlen(var) + strlen(value) + 2);
           if(string != NULL){
               strcpy(string, var);
               strcat(string, "=");
               strcat(string, value);
           }
           printf("calling putenv with string %s\n", string);
           if(putenv(string) != 0){
               fprintf(stderr, "putenv failed!\n");
               free(string);
               exit(1);
           }
           value = getenv(var);
           if(value){
               printf("new value of %s is %s\n", var, value);
           }else{
               printf("calling get env failed!\n");
           }
       }
       return 0;
   }
   

   获取所有环境变量

   #include
   #include
   extern char** environ;
   int main(int argc, char *argv[]){
       char **env = environ;
       while(*env != NULL){
           printf("%s\n", *env);
           env++;
       }
       return 0;
   }
   

4. 日期与时间

   • time函数获取时间，返回time_t类型的长整型数，表示某一特定时间到现在的秒数

     
     
     

     #include
     #include
     #include
     int main(int argc, char *argv[]){
         int i;
         time_t the_time;
         for(i = 0;i<10; i++){
             the_time = time((time_t*)0);
             printf("time is:%ld\n", the_time);
             sleep(2);
         }
         return 0;
     }
     

   • gmtime可以从time_t类型的数据中获取当前时间数据

     
     
     
     
     

     返回tm结构体类型的指针，其中包含了我们需要的各种信息

     
     
     

     #include
     #include
     int main(){
         time_t the_time;
         time(&the_time);
         struct tm* tm_ptr = gmtime(&the_time);
         printf("the row time is:%ld\n", the_time);
         printf("the gmtime gives:\n");
         printf("date: %02d/%02d/%02d\n", tm_ptr->tm_year, tm_ptr->tm_mon + 1, tm_ptr->tm_mday);
         printf("time: %02d:%02d:%02d\n", tm_ptr->tm_hour, tm_ptr->tm_min, tm_ptr->tm_sec);
         return 0;
     }
     

   • localtime 用来返回time_t类型代表的本地时间

     #include
     #include
     int main(){
         time_t the_time;
         time(&the_time);
         struct tm* tm_ptr = localtime(&the_time);
         printf("the row time is:%ld\n", the_time);
         printf("the localtime gives:\n");
         printf("date: %02d/%02d/%02d\n", tm_ptr->tm_year, tm_ptr->tm_mon + 1, tm_ptr->tm_mday);
         printf("time: %02d:%02d:%02d\n", tm_ptr->tm_hour, tm_ptr->tm_min, tm_ptr->tm_sec);
         return 0;
     }
     

   • mktime从一个tm结构体构造一个等价的time_t值，失败时返回-1

     
     
     

   • asctime and ctime

     
     
     

     #include
     #include
     int main(){
         struct tm* tm_ptr;
         time_t the_time;
         time(&the_time);
         printf("asctime gives:%s\n", asctime(localtime(&the_time)));
         printf("ctime gives:%s\n", ctime(&the_time));
         return 0;
     }
     

5. 临时文件

   • 使用tmpnam生成临时文件名称

     
     
     
     
     

     使用tmpfile打开临时文件

     
     
     

     #include
     int main(){
         char tmpname[L_tmpnam];
         char* filename;
         FILE* tempfile;
         filename = tmpnam(tmpname);
         printf("the tmp file name is:%s\n", filename);
         tempfile = tmpfile();
         if(tempfile){
             puts("open stream to tmpfile successfully!");
         }else{
             puts("open file failed!");
         }
         return 0;
     }
     

   使用mktemp与mkstemp

   
   
   

6. 使用syslog记录日志

   #include
   #include
   int main(){
       FILE* f = fopen("no_exist", "r");
       if(!f){
           syslog(LOG_ALERT | LOG_USER, "oops - %m\n");
           puts("log successfully!\n");
       }
       return 0;
   }
   

   
   
   

   掌握理解，openlog, setlogmask

   #include
   #include
   #include
   int main(){
       int logmask;
       openlog("test logmask", LOG_PID|LOG_CONS, LOG_USER);
       syslog(LOG_DEBUG, "test debug log, this message should exist!");
       syslog(LOG_INFO, "program pid is %d\n", getpid());
       logmask = setlogmask(LOG_UPTO(LOG_INFO));
       syslog(LOG_DEBUG, "this message should not exist!\n");
       return 0;
   }