Question

我有一个for循环，如：

        ofstream myfile;
        myfile.open ("clnt.txt",std::ofstream::out | std::ofstream::app);
        struct timeval  tv;
        gettimeofday(&tv, NULL);
        for(int i=0;i<100;i++)
        {
                double time_in_mill1 = 
                 (tv.tv_sec) * 1000 + (tv.tv_usec) / 1000 ; 
                cout<<time_in_mill1<<endl;
                int n1=sprintf (den, "%lf",  time_in_mill1);
                printf ("[%s] is a string %d chars long\n",den,n1);
                myfile << den;
        }

并且在clnt.txt文件中所有值都是'-2090430839.000000'，屏幕'-2.09043e + 09'是为所有time_in_mill1值写的。我预计至少有两个值会有所不同。我究竟做错了什么？

Answer 1

您需要将gettimeofday移动到循环中并纠正除法

for(int i=0;i<100;i++)
{
    gettimeofday(&tv, NULL);
    double time_in_mill1 = 
      (tv.tv_sec) * 1000 + (tv.tv_usec) / 1000.0 ; 
    ...
 }

Answer 2

我忘了更新gettimeofday（）。现在每个价值都彼此不同。谢谢你的所有答案。

ofstream myfile;
myfile.open ("clnt.txt",std::ofstream::out | std::ofstream::app);
struct timeval  tv;
gettimeofday(&tv, NULL);

    for(int i=0;i<100;i++)
    {
              gettimeofday(&tv, NULL);
              double time_in_mill1 = 
              (tv.tv_sec) * 1000 + (tv.tv_usec) / 1000.0 ; 
              cout<<time_in_mill1<<endl;
              int n1=sprintf (den, "%lf",  time_in_mill1);
              printf ("[%s] is a string %d chars long\n",den,n1);
              myfile << den;
     }

for循环中c ++中的时间（以毫秒为单位）始终相同

2 个答案: