time_t tm timeval 和 时间字符串的转换方法
<p><span><strong>1、常用的时间存储方式 </strong></span></p><p>1）tml">time_t类型，这本质上是一个长整数，表示从1970-01-01 00:00:00到目前计时时间的秒数，如果需要更精确一点的，可以使用timeval精确到毫秒。 </p>
<p>2）tm结构，这本质上是一个结构体，里面包含了各时间字段 </p>
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<div class="line number1 index0 alt2"><code class="xhtml plain">struct tm { </code></div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_sec; /* seconds after the minute - */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_min; /* minutes after the hour - */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_hour; /* hours since midnight - */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_mday; /* day of the month - */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_mon; /* months since January - */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_year; /* years since 1900 */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_wday; /* days since Sunday - */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_yday; /* days since January 1 - */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int tm_isdst; /* daylight savings time flag */ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">}; </code>
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<p> 其中tm_year表示从1900年到目前计时时间间隔多少年，如果是手动设置值的话，tm_isdst通常取值-1。 <br></p>
<p>3）struct timeval结构体在time.h中的定义为<br></p>
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<div class="line number1 index0 alt2"><code class="xhtml plain">struct timeval {</code></div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">time_t tv_sec; /* seconds */</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">suseconds_t tv_usec; /* microseconds */</code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">};</code>
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<p><span><strong>2、常用的时间函数 <br></strong></span></p>
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<div class="line number1 index0 alt2"><code class="xhtml plain">time_t time(time_t *t); //取得从1970年1月1日至今的秒数 </code></div>
<div class="line number2 index1 alt1"> </div>
<div class="line number3 index2 alt2"><code class="xhtml plain">char *asctime(const struct tm *tm); //将结构中的信息转换为真实世界的时间，以字符串的形式显示 </code></div>
<div class="line number4 index3 alt1"> </div>
<div class="line number5 index4 alt2"><code class="xhtml plain">char *ctime(const time_t *timep); //将timep转换为真是世界的时间，以字符串显示，它和asctime不同就在于传入的参数形式不一样 </code></div>
<div class="line number6 index5 alt1"> </div>
<div class="line number7 index6 alt2"><code class="xhtml plain">struct tm *gmtime(const time_t *timep); //将time_t表示的时间转换为没有经过时区转换的UTC时间，是一个struct tm结构指针 </code></div>
<div class="line number8 index7 alt1"> </div>
<div class="line number9 index8 alt2"><code class="xhtml plain">struct tm *localtime(const time_t *timep); //和gmtime类似，但是它是经过时区转换的时间。 </code></div>
<div class="line number10 index9 alt1"> </div>
<div class="line number11 index10 alt2"><code class="xhtml plain">time_t mktime(struct tm *tm); //将struct tm 结构的时间转换为从1970年至今的秒数 </code></div>
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<div class="line number13 index12 alt2"><code class="xhtml plain">int gettimeofday(struct timeval *tv, struct timezone *tz); //返回当前距离1970年的秒数和微妙数，后面的tz是时区，一般不用 </code></div>
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<div class="line number15 index14 alt2"><code class="xhtml plain">double difftime(time_t time1, time_t time2); //返回两个时间相差的秒数 </code></div>
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<p><span><strong>3、时间与字符串的转换 <br></strong></span></p>
<p>需要包含的头文件如下 </p>
<p>#include <iostream> <br>
#include <time.h> <br>
#include <stdlib.h> <br>
#include <string.h> <br></p>
<p><strong>1）unix/windows下时间转字符串参考代码 <br></strong></p>
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<div class="line number1 index0 alt2"><code class="xhtml plain">time_t t; //秒时间 </code></div>
<div class="line number2 index1 alt1"><code class="xhtml plain">tm* local; //本地时间 </code></div>
<div class="line number3 index2 alt2"><code class="xhtml plain">tm* gmt; //格林威治时间 </code></div>
<div class="line number4 index3 alt1"><code class="xhtml plain">char buf= {0}; </code></div>
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<code class="xhtml spaces"> </code> </div>
<div class="line number6 index5 alt1"><code class="xhtml plain">t = time(NULL); //或者time(&t);//获取目前秒时间 </code></div>
<div class="line number7 index6 alt2"><code class="xhtml plain">local = localtime(&t); //转为本地时间 </code></div>
<div class="line number8 index7 alt1"><code class="xhtml plain">strftime(buf, 64, "%Y-%m-%d %H:%M:%S", local); </code></div>
<div class="line number9 index8 alt2"><code class="xhtml plain">std::cout << buf << std::endl; </code></div>
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<code class="xhtml spaces"> </code> </div>
<div class="line number11 index10 alt2"><code class="xhtml plain">gmt = gmtime(&t);//转为格林威治时间 </code></div>
<div class="line number12 index11 alt1"><code class="xhtml plain">strftime(buf, 64, "%Y-%m-%d %H:%M:%S", gmt); </code></div>
<div class="line number13 index12 alt2"><code class="xhtml plain">std::cout << buf << std::endl; </code></div>
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<p><strong>2）unix字符串转时间参考代码 </strong></p>
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<div class="line number1 index0 alt2"><code class="xhtml plain">tm tm_; </code></div>
<div class="line number2 index1 alt1"><code class="xhtml plain">time_t t_; </code></div>
<div class="line number3 index2 alt2"><code class="xhtml plain">char buf= {0}; </code></div>
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<code class="xhtml spaces"> </code> </div>
<div class="line number5 index4 alt2"><code class="xhtml plain">strcpy(buf, "2012-01-01 14:00:00"); </code></div>
<div class="line number6 index5 alt1"><code class="xhtml plain">strptime(buf, "%Y-%m-%d %H:%M:%S", &tm_); //将字符串转换为tm时间 </code></div>
<div class="line number7 index6 alt2"><code class="xhtml plain">tm_.tm_isdst = -1; </code></div>
<div class="line number8 index7 alt1"><code class="xhtml plain">t_ = mktime(&tm_); //将tm时间转换为秒时间 </code></div>
<div class="line number9 index8 alt2"><code class="xhtml plain">t_ += 3600; //秒数加3600 </code></div>
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<code class="xhtml spaces"> </code> </div>
<div class="line number11 index10 alt2"><code class="xhtml plain">tm_ = *localtime(&t_);//输出时间 </code></div>
<div class="line number12 index11 alt1"><code class="xhtml plain">strftime(buf, 64, "%Y-%m-%d %H:%M:%S", &tm_); </code></div>
<div class="line number13 index12 alt2"><code class="xhtml plain">std::cout << buf << std::endl; </code></div>
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<p><strong>3）由于windows下没有strptime函数，所以可以使用scanf来格式化 <br></strong></p>
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<div class="line number1 index0 alt2"><code class="xhtml plain">time_t StringToDatetime(char *str) </code></div>
<div class="line number2 index1 alt1"><code class="xhtml plain">{ </code></div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm tm_; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">int year, month, day, hour, minute,second; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">sscanf(str,"%d-%d-%d %d:%d:%d", &year, &month, &day, &hour, &minute, &second); </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm_.tm_year = year-1900; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm_.tm_mon = month-1; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm_.tm_mday = day; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm_.tm_hour = hour; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm_.tm_min = minute; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm_.tm_sec = second; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">tm_.tm_isdst = 0; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">time_t t_ = mktime(&tm_); //已经减了8个时区 </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return t_; //秒时间 </code>
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<div class="line number16 index15 alt1"><code class="xhtml plain">} </code></div>
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<p><strong>4）timeval获取时间示例：</strong></p>
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<div class="line number1 index0 alt2"><code class="xhtml plain">struct timeval start_time, over_time, consume_time;</code></div>
<div class="line number2 index1 alt1"><code class="xhtml plain">gettimeofday(&over_time, NULL);//get the current time</code></div>
<div class="line number3 index2 alt2"><code class="xhtml plain">start_time = over_time;</code></div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">do something.....</code>
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<div class="line number5 index4 alt2"><code class="xhtml plain">gettimeofday(&over_time, NULL);</code></div>
<div class="line number6 index5 alt1"> </div>
<div class="line number7 index6 alt2"><code class="xhtml plain">timeval_subtract(&consume_time, &start_time, &over_time);//计算时间差104./** </code></div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">* 计算两个时间的间隔，得到时间差 </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">* @param struct timeval* resule 返回计算出来的时间 </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">* @param struct timeval* x 需要计算的前一个时间 </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">* @param struct timeval* y 需要计算的后一个时间 </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">* return -1 failure ,0 success </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">**/ </code>
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<div class="line number14 index13 alt1"><code class="xhtml plain">timeval_subtract(struct timeval* result, struct timeval* x, struct timeval* y) </code></div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">{ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">if ( x->tv_sec>y->tv_sec ) </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return -1; </code>
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<code class="xhtml spaces"> </code> </div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">if ( (x->tv_sec==y->tv_sec) && (x->tv_usec>y->tv_usec) ) </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return -1; </code>
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<code class="xhtml spaces"> </code> </div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">result->tv_sec = ( y->tv_sec-x->tv_sec ); </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">result->tv_usec = ( y->tv_usec-x->tv_usec ); </code>
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<code class="xhtml spaces"> </code> </div>
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<code class="xhtml spaces"> </code><code class="xhtml plain">if (result->tv_usec<</code><code class="xhtml keyword">0</code><code class="xhtml plain">) </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">{ </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">result->tv_sec--; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">result->tv_usec+=1000000; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">} </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">return 0; </code>
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<code class="xhtml spaces"> </code><code class="xhtml plain">}</code>
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<p><span><strong>4、关于localtime与localtime_r的区别</strong></span></p>
<p><span>struct tm *localtime(const time_t *timep);</span></p>
<p>这个函数在返回的时候，返回的是一个指针，实际的内存是localtime内部通过static申请的静态内存，所以通过localtime调用后的返回值不及时使用的话，很有可能被其他线程localtime调用所覆盖掉</p>
<p><span>struct tm *localtime_r(const time_t *timep, struct tm *result);</span></p>
<p>localtime_r则是由调用者在第二个参数传入一个struct tm result指针，该函数会把结果填充到这个传入的指针所指内存里面；成功的返回值指针也就是struct tm result。</p>
<p>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。</p>
<p>其他的时间函数，如asctime，asctime_r；ctime，ctime_r；gmtime，gmtime_r都是类似的，所以，<strong>时间函数的 _r 版本都是线程安全的。</strong><br>
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<p>以上这篇time_t tm timeval 和 时间字符串的转换方法就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。</p>
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