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Defined in header <ctime> | ||
std::clock_t clock(); | ||
Returns the approximate processor time used by the process since the beginning of an implementation-defined era related to the program's execution. To convert result value to seconds divide it byCLOCKS_PER_SEC.
Only the difference between two values returned by different calls tostd::clock is meaningful, as the beginning of thestd::clock era does not have to coincide with the start of the program.
std::clock time may advance faster or slower than the wall clock, depending on the execution resources given to the program by the operating system. For example, if the CPU is shared by other processes,std::clock time may advance slower than wall clock. On the other hand, if the current process is multithreaded and more than one execution core is available,std::clock time may advance faster than wall clock.
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Processor time used by the program so far.
Throws nothing.
On POSIX-compatible systems,clock_gettime with clock idCLOCK_PROCESS_CPUTIME_ID offers better resolution.
The value returned byclock() may wrap around on some implementations. For example, on such an implementation, ifstd::clock_t is a signed 32-bit integer andCLOCKS_PER_SEC is1'000'000, it will wrap after about 2147 seconds (about 36 minutes).
This example demonstrates the difference betweenclock() time and real time.
#include <chrono>#include <ctime>#include <iomanip>#include <iostream>#include <thread> // The function f() does some time-consuming work.void f(){volatiledouble d=0;for(int n=0; n!=10000;++n)for(int m=0; m!=10000;++m) d+= d* n* m;} int main(){conststd::clock_t c_start= std::clock();auto t_start=std::chrono::high_resolution_clock::now();std::thread t1(f);std::thread t2(f);// f() is called on two threads t1.join(); t2.join();conststd::clock_t c_end= std::clock();constauto t_end=std::chrono::high_resolution_clock::now(); std::cout<<std::fixed<<std::setprecision(2)<<"CPU time used: "<<1000.0*(c_end- c_start)/CLOCKS_PER_SEC<<"ms\n"<<"Wall clock time passed: "<<std::chrono::duration<double,std::milli>(t_end- t_start)<<'\n';}
Possible output:
CPU time used: 1590.00msWall clock time passed: 808.23ms
| converts astd::time_t object to a textual representation (function)[edit] | |
| returns the current time of the system as time since epoch (function)[edit] | |
C documentation forclock | |
