We can find out the time taken by different parts of a program by using the std::chrono library introduced in C++ 11. We have discussed at How to measure time taken by a program in C. The functions described there are supported in C++ too but they are C specific. For clean and robust C++ programs we should strive to use C++ specific language constructs only.
std::chrono has two distinct objects–timepoint and duration. A timepoint as the name suggests represents a point in time whereas a duration represents an interval or span of time. The C++ library allows us to subtract two timepoints to get the interval of time passed in between. Using provided methods we can also convert this duration to appropriate units.
The std::chrono provides us with three clocks with varying accuracy. The high_resolution_clock is the most accurate and hence it is used to measure execution time.
Step 1: Get the timepoint before the function is called
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#include <chrono>
using namespace std::chrono;
// Use auto keyword to avoid typing long
// type definitions to get the timepoint
// at this instant use function now()
auto start = high_resolution_clock::now();
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Step 2: Get the timepoint after the function is called
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`#include <chrono>`
`using` `namespace` `std::chrono;`
`// After function call`
`auto` `stop = high_resolution_clock::now();`
Step 3: Get the difference in timepoints and cast it to required units
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// Subtract stop and start timepoints and
// cast it to required unit. Predefined units
// are nanoseconds, microseconds, milliseconds,
// seconds, minutes, hours. Use duration_cast()
// function.
auto duration = duration_cast<microseconds>(stop - start);
// To get the value of duration use the count()
// member function on the duration object
cout << duration.count() << endl;
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A complete C++ program demonstrating the procedure is given below. We fill up a vector with some random numbers and measure the time taken by sort() function to sort this vector.
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// C++ program to find out execution time of
// of functions
#include <algorithm>
#include <chrono>
#include <iostream>
#include<vector>
using namespace std;
using namespace std::chrono;
// For demonstration purpose, we will fill up
// a vector with random integers and then sort
// them using sort function. We fill record
// and print the time required by sort function
int main()
{
vector<``int``> values(10000);
// Generate Random values
auto f = []() -> int { return rand``() % 10000; };
// Fill up the vector
generate(values.begin(), values.end(), f);
// Get starting timepoint
auto start = high_resolution_clock::now();
// Call the function, here sort()
sort(values.begin(), values.end());
// Get ending timepoint
auto stop = high_resolution_clock::now();
// Get duration. Substart timepoints to
// get durarion. To cast it to proper unit
// use duration cast method
auto duration = duration_cast<microseconds>(stop - start);
cout << "Time taken by function: "
<< duration.count() << " microseconds" << endl;
return 0;
}
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Output: (Machine Dependent)
<pre style="box-sizing: border-box; margin: 0px 0px 10px; padding: 20px; border: 0px; font-size: 12pt; vertical-align: baseline; background-color: var(--gfg-grey-bg); border-radius: 10px; color: var(--color-black); font-family: Consolas, monospace; overflow: auto; white-space: pre;">Time taken by function: 3062 microseconds</pre>
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