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HomeOperation and MaintenanceLinux Operation and MaintenanceIs there a function to get time in linux?

Linux has a function to get the time. Commonly used time functions in Linux: 1. time() function to obtain the current time; 2. "localtime_r"() and localtime() functions to obtain the current local time and date; 3. gettimeofday() function to obtain the current time time.

Is there a function to get time in linux?

#The operating environment of this tutorial: linux7.3 system, Dell G3 computer.

Linux function to obtain time

Introduction to commonly used time functions:

  1. ##time() function obtains the current time
    #include <time.h>
    time_t time(time_t *t);  
    
    /* 此函数会返回从公元1970年1月1日的UTC时间从0时0分0秒算起到现在所经过的秒数。
     * 如果t 并非空指针的话,此函数也会将返回值存到t指针所指的内存。
     */</time.h>
    Example code:

    #include <stdio.h>
    #include <string.h>
    #include <time.h>
    
    int main()
    {
        time_t sec;
    
        sec = time((time_t *)NULL);
        printf("%d\n", (int)sec);
    
        return 0;
    }</time.h></string.h></stdio.h>
    Running results:

  2. ## localtime_r() localtime() obtains the current local time and Date

    #include <time.h>
           
        struct tm *localtime(const time_t *timep);
        struct tm *localtime_r(const time_t *timep, struct tm *result);
            
    /*该函数将有time函数获取的值timep转换真实世界所使用的时间日期表示方法,然后将结果由结构tm返回*/
    
    /**需要注意的是localtime函数可以将时间转换本地时间,但是localtime函数不是线程安全的。
    多线程应用里面,应该用localtime_r函数替代localtime函数,因为localtime_r是线程安全的**/</time.h>
    Instance code:

    #include <stdio.h>
    #include <string.h>
    #include <time.h>
    
    int main()
    {
        time_t tmp;   
        struct tm *timp; 
       
        time(&tmp);   
        timp = localtime(&tmp);
       
        printf("%d-%d-%d %d:%d:%d\n", (1900 + timp->tm_year), ( 1 + timp->tm_mon), timp->tm_mday,
                                    (timp->tm_hour), timp->tm_min, timp->tm_sec); 
    
        return 0;
    }</time.h></string.h></stdio.h>

    Running result:

  3. ## asctime( ) asctime_r() returns the time and date in string format
  4. #include <time.h>
           
        struct tm *gmtime(const time_t *timep);
        struct tm *gmtime_r(const time_t *timep, struct tm *result);
           
        char *asctime(const struct tm *tm);
        char *asctime_r(const struct tm *tm, char *buf);
           
           
    /*
     *gmtime是把日期和时间转换为格林威治(GMT)时间的函数。
     *将参数time 所指的time_t 结构中的信息转换成真实世界所使用的时间日期表示方法,然后将结果由结构tm返回
     *asctime 将时间以换为字符串字符串格式返回 
     */</time.h>
    Example code:
    #include <stdio.h>
    #include <string.h>
    #include <time.h> 
      
    int main() 
    {   
        time_t timp;   
        time(&timp);
       
        printf("%s\n", asctime(gmtime(&timp)));   
        
        return 0;
    }</time.h></string.h></stdio.h>
    Running results: (

    The string obtained by asctime itself has a newline character

    )

    ## ctime(), ctime_r() represents the time and date in string format
  5. #include <time.h>
    char *ctime(const time_t *timep);
    char *ctime_r(const time_t *timep, char *buf);
    
    
    /*
     *ctime()将参数timep所指的time_t结构中的信息转换成真实世界所使用的时间日期表示方法,
     *然后将结果以字符串形态返回
     */</time.h>

    Example code:

    #include <stdio.h>
    #include <string.h>
    #include <time.h>   
    
    int main(void)   
    {   
        time_t tmp;
     
        time(&tmp);   
        printf("%s\n", ctime(&tmp));
        
        return 0;  
    }</time.h></string.h></stdio.h>
    Run result: (

    ctime

    The obtained string itself has a newline character

    )

    mktime() Converts the value of the time structure struct tm into elapsed seconds
  6.  #include <time.h>
     time_t mktime(struct tm *tm);
    
    /*
     *将时间结构体struct tm的值转化为经过的秒数
     */</time.h>

    Example code:

    #include <stdio.h>
    #include <string.h>
    #include <time.h>  
     
    int main()   
    {   
        time_t tmp;   
        struct tm *timp;   
    
        time(&tmp);   
        timp = localtime(&tmp);   
        tmp = mktime(timp);
       
        printf("%d\n", (int)tmp);   
        
        return 0;
    }</time.h></string.h></stdio.h>
    Run result:

    ## gettimeofday() Gets the current time

  7. #include <sys>
    
    int gettimeofday(struct timeval *tv, struct timezone *tz);
        
    struct timeval {
        time_t      tv_sec;     /* seconds (秒)*/
        suseconds_t tv_usec;    /* microseconds(微秒) */
        };
    struct timezone {
        int tz_minuteswest;     /* minutes west of Greenwich */
        int tz_dsttime;         /* type of DST correction */
        };
    /*
     *gettimeofday函数获取当前时间存于tv结构体中,相应的时区信息则存于tz结构体中
     *需要注意的是tz是依赖于系统,不同的系统可能存在获取不到的可能,因此通常设置为NULL
     */</sys>
  8. Example code:

    #include <stdio.h>
    #include <string.h>
    #include <sys>
    
    int main()
    {
        struct timeval tv; 
        
        gettimeofday(&tv, NULL);
    
        printf("tv_sec = %d\n", (int)tv.tv_sec);
        printf("tv_usec = %d\n", (int)tv.tv_usec);
        
        return 0;
    }</sys></string.h></stdio.h>
    Running results:

    Recommended learning: Linux video tutorial

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