Question

struct timeval start, end, duration;
gettimeofday(&start, NULL);

res = curl_easy_perform(curl);

gettimeofday(&end, NULL);
timersub(&end, &start, &duration);

tm* startTime = localtime(&start.tv_sec);
tm* endTime = localtime(&end.tv_sec);
char buf[64];
strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", startTime);
char buf2[64];
strftime(buf2, sizeof(buf2), "%Y-%m-%d %H:%M:%S", endTime);

ofstream timeFile;
timeFile.open ("timingSheet.txt");
timeFile << fixed << showpoint;
timeFile << setprecision(6);
timeFile << "Duration: " << duration.tv_sec << "." << duration.tv_usec << " seconds \n";
timeFile << "Start time: " <<  buf <<"." << start.tv_usec << "\n";
timeFile << "End time: " <<  buf2 <<"." << end.tv_usec << "\n";
timeFile.close();

当我运行此代码时，我得到了这个输出：

Duration: 3.462243 seconds 
Start time: 2012-05-15 17:14:07.432613
End time: 2012-05-15 17:14:07.894856

让我感到困惑的是，持续时间值与开始和结束时间不匹配。这两个日期仅相差微秒。是否有一个原因？

谢谢！

Answer 1

localtime返回一个静态分配的缓冲区并调用它两次，因此StartTime和EndTime是相同的。您需要在每次调用后直接将其复制到另一个缓冲区中。

tm* startTime = localtime(&start.tv_sec); 
char buf[64]; 
strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", startTime); 

tm* endTime = localtime(&end.tv_sec); 
char buf2[64]; 
strftime(buf2, sizeof(buf2), "%Y-%m-%d %H:%M:%S", endTime);

编辑：你也可以这样写：

tm* pTimeBuf = localtime(&start.tv_sec); 
char buf[64]; 
strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", pTimeBuf); 

localtime(&end.tv_sec); // NB. I don't store th return value (since I have it already)
char buf2[64]; 
strftime(buf2, sizeof(buf2), "%Y-%m-%d %H:%M:%S", pTimeBuf);

Answer 2

我同意Edwin的观点，只是一个小修改，它更好地使用线程安全版本localtime_r而不是localtime

struct tm startTime,endTime;
memset(&startTime,0,sizeof(struct tm)); //Advisable but not necessary
memset(&endTime,0,sizeof(struct tm)); //Advisable but not necessary
localtime_r(&start.tv_sec, &startTime);
localtime_r(&end.tv_sec, &endTime);

时间不匹配

2 个答案: