How to Use the gettimeofday () function of Linux time functions

I. How to Use the gettimeofday () function:

1. Introduction:

In C language, you can use the gettimeofday () function to get the time. Its precision can reach a subtle level

2. function prototype:

# Include <sys/time. h>

Int gettimeofday (struct timeval * TV, struct timezone * tz)

3. Description:

Gettimeofday () will return the current time using the TV struct, and put the information of the local time zone in the structure referred to by TZ

4. struct:

1> timeval

Struct timeval {

Long TV _sec;/* seconds */

Long TV _usec;/* subtle */

};

2> the timezone structure is defined:

Struct timezone {

Int tz_minuteswest;/* the time difference between Greenwich and */

Int tz_dsttime;/* type of DST correction */

}

3> In the gettimeofday () function, either TV or TZ can be empty. If it is null, the corresponding struct is not returned.

4> if the function is successfully executed, 0 is returned. If the function fails,-1 is returned. The error code is stored in errno.

5. program instance:

# Include <stdio. h>
# Include <sys/time. h>

# Include <unistd. h>

 

Int main ()

{

Struct timeval TV;

Struct timezone TZ;

Gettimeofday (& TV, & Tz );

 

Printf ("TV _sec: % d \ n", TV. TV _sec );

Printf ("TV _usec: % d \ n", TV. TV _usec );

Printf ("tz_minuteswest: % d \ n", tz. tz_minuteswest );

Printf ("tz_dsttime: % d \ n", tz. tz_dsttime );

}

Note: when using the gettimeofday () function, the second parameter is generally null, because we generally only get the current time, instead of getting the value of timezone

2. A common method for gettimeofday () Functions

When testing a program, you often need to know the time required for program execution. In Linux, you can use the gettimeofday function to get the time.

1. program instance:

Time required to test the call to the delya () function (unit: subtle)

# Include <stdio. h>

# Include <sys/time. h>

# Include <unistd. h>

 

Int delay (INT time)

{

Int I, J;

For (I = 0; I <time; I ++)

For (j = 0; j <5000; j ++)

;

}

 

Int main ()

{

Struct timeval start;

Struct timeval end;

Unsigned long diff;

Gettimeofday (& START, null );

Delay (10 );

Gettimeofday (& End, null );

Diff = 1000000 * (end. TV _sec-start. TV _sec) + end. TV _usec-start. TV _usec;

Printf ("thedifference is % LD \ n", diff );

Return 0;

}

Note:

This method can be used to detect the time used to call the delay () function.