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<stdio.h>
  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;
  }

使用getopt处理命令行参数

#include<stdio.h>
#include<unistd.h>
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<stdio.h>
#include<unistd.h>
#include<getopt.h>
#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;
}

使用getenv与putenv获取并设置环境变量

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

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<time.h>
  #include<stdio.h>
  #include<unistd.h>
  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<stdio.h>
  #include<time.h>
  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<stdio.h>
  #include<time.h>
  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<time.h>
  #include<stdio.h>
  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;
  }
  

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<stdio.h>
  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

使用syslog记录日志

#include<syslog.h>
#include<stdio.h>
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<syslog.h>
#include<stdio.h>
#include<unistd.h>
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;
}