mktime时间的转换

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我是靠谱客的博主俊逸红牛，最近开发中收集的这篇文章主要介绍mktime时间的转换，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

最近在分析一些log的时候需要进行时间的处理，log中的时间格式是这样的："05/Jan/2015:16:12:15"。由于需要计算两个时间的差值，所以将其转换成数字进行处理会比较方便。

于是先解析这个字符串，提取相应的字段，然后用mktime转换成time_t。结果在ubuntu上测试没问题，在android上却出现计算出来的时间比输入的时间少了3600s。

原来是需要把struct tm中的tm_isdst设置成0。这个字段对于北京时间来说应该程序中主动设为0, 否则系统可能把它设成1，造成偏差。

另外，北京时间比UTC/GMT时间早8个小时: http://www.worldtimeserver.com/current_time_in_CN.aspx

time（NULL）得到的是UTC时间，但是如果你把转换成localtime，再转换成UTC时间，就会发现两者差28800s，即8小时。

下面是一些验证性代码以供参考：

#include 
   
   
    
    
#include 
    
    
     
     
#include 
     
     
      
      
#include 
      
      
       
       
#include 
       
       
         struct tm parseTime(const char* ts) { // Format like "05/Jan/2015:16:12:15 +0800" printf("timeFromString:%sn", ts); const char *Monthes[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jly", "Aug", "Sep", "Oct", "Nov", "Dec"}; const int DAY_IDX = 0; const int MON_IDX = 1; const int YEAR_IDX = 2; const int HOUR_IDX = 3; const int MIN_IDX = 4; const int SEC_IDX = 5; const int intervals[6] = {3, 4, 5, 3, 3, 3}; int vals[6]; char buf[5]; for (int i=0; i<6; ++i) { //snprintf(buf, intervals[i], "%s", ts); strncpy(buf, ts, intervals[i]-1); buf[intervals[i]-1] = ''; ts += intervals[i]; if (i == 1) { for (int j=1; j<=12; ++j) { if (!strncmp(buf, Monthes[j-1], 3)) { vals[i] = j; break; } } } else { vals[i] = atoi(buf); } //printf("buf:%s, %dn", buf, vals[i]); } struct tm y2k; y2k.tm_year = vals[YEAR_IDX] - 1900; y2k.tm_mon = vals[MON_IDX] - 1 ; y2k.tm_mday = vals[DAY_IDX]; y2k.tm_hour = vals[HOUR_IDX]; y2k.tm_min = vals[MIN_IDX]; y2k.tm_sec = vals[SEC_IDX];; y2k.tm_isdst = 0; // important for Chinese time! no dst! return y2k; } time_t localTimeFromString(const char* ts) { struct tm y2k = parseTime(ts); return mktime(&y2k); } time_t localTimeToUTC(const char* ts) { time_t result; struct tm y2k = parseTime(ts); #if 0 result = mktime(&y2k) - timezone; printf("timezone:%ldn", timezone); //printf("mktime:%ldn", result); #else char *oldTZ = getenv("TZ"); putenv("TZ=UTC"); tzset(); result = mktime(&y2k); //printf("mktime:%ldn", result); printf("timezone:%ldn", timezone); if(oldTZ == NULL) { putenv("TZ="); } else { char buf[256]; sprintf(buf, "TZ=%s", oldTZ); putenv(buf); } tzset(); #endif return result; } int formatTime(time_t t, char *buf, int maxsize) { const char* format = "%d/%b/%Y:%H:%M:%Sn"; struct tm *tmp; tmp = localtime(&t); if (tmp == NULL) { perror("localtime"); return -1; } if (strftime(buf, maxsize, format, tmp) == 0) { fprintf(stderr, "strftime returned 0"); return -1; } return 0; } int main () { time_t now = time(NULL); char buf[256] = {0}; formatTime(now, buf, 256); printf("formatedString:%sn", buf); time_t nt = localTimeFromString(buf); printf("oldtime:%ldnnewtime:%ldn", now, nt); const char *s = "01/Jan/1970:00:00:00"; time_t utcT = localTimeToUTC(s); printf("timer: %ld, utcT:%ldn", time(NULL), utcT); utcT = localTimeToUTC(buf); printf("now: %ldnutcT:%ldndiff:%fn", now, utcT, difftime(utcT, now)); return 0; }