計算時間差，標準C提供了difftime函數，它的原型：double difftime( time_t timer1,time_t timer0);下面的這段代碼編譯沒問題
#include <time.h>
int _tmain(int argc, _TCHAR* argv[])
{
time_t* start, *finish;
start=NULL;
finish=NULL;
long loop;
double result, elapsed_time;
printf( "Multiplying 2 floating point numbers 500 million times...\n" );
time( start );
start=&temp1;
for( loop = 0; loop < 500000000; loop++ )
result = 3.63 * 5.27;
time( finish);
elapsed_time = difftime( *finish, *start );
printf( "\nProgram takes %lf seconds.\n", elapsed_time );
return 0;
}
運行卻有異常，linux直接core dump。通過調試跟蹤，發現在使用了指針start和finish都是null;
time函數的形參是time_t *timer，但是在這里卻不能是指針，為了使程序運行，我們可以使用下面的代碼
#include <time.h>
int _tmain(int argc, _TCHAR* argv[])
{
time_t* start, *finish;
time_t temp1;
time_t temp2;
start=NULL;
finish=NULL;
long loop;
double result, elapsed_time;
printf( "Multiplying 2 floating point numbers 500 million times...\n" );
time( &temp1 );
start=&temp1;
for( loop = 0; loop < 500000000; loop++ )
result = 3.63 * 5.27;
time( &temp1+sizeof(time_t) );
finish=&temp1+sizeof(time_t);
elapsed_time = difftime( *finish, *start );
printf( "\nProgram takes %6.0f seconds.\n", elapsed_time );
return 0;
}
也可以在用temp2來替代&temp1+sizeof(time_t)