Category: C++

Speed up by ignoring std::cout

Posted on by admin

Test Code

  1. #include <iostream>
  2.  
  3. int main(int argc, char *argv[])
  4. {
  5. 	//std::cout.setstate(std::ios_base::badbit);
  6. 	for(int i = 0; i < 100; i ++) {
  7. 		for(int i = 0; i < 100; i ++) {
  8. 			;//std::cout << "" << std::endl;
  9. 		}
  10. 	}
  11. 	return 0;
  12. }

Test it without std::cout

  1. root@imx6ul7d:~/tmp# time ./t1_1 
  2.  
  3. real    0m0.041s
  4. user    0m0.020s
  5. sys     0m0.000s

Test it with std::cout, but redirect to /dev/null

  1. root@imx6ul7d:~/tmp# time ./t1_0 > /dev/null
  2.  
  3. real    0m0.096s
  4. user    0m0.030s
  5. sys     0m0.030s

Test it with std::cout, but set io state

  1. root@imx6ul7d:~/tmp# time ./t1_2
  2.  
  3. real    0m0.061s
  4. user    0m0.040s
  5. sys     0m0.000s

Profile : Linux

Posted on by admin

Example 1

Add -pg

  1. arm-linux-gnueabihf-g++ -Wall -g -pg hello.cpp -o hello -std=c++17

Test

  1. root@imx6ul7d:~# gprof -b hello 
  2. Flat profile:
  3.  
  4. Each sample counts as 0.01 seconds.
  5.   %   cumulative   self              self     total           
  6.  time   seconds   seconds    calls   s/call   s/call  name    
  7. 100.00      3.45     3.45        1     3.45     3.45  hehe()
  8.   0.00      3.45     0.00        4     0.00     0.00  std::_Optional_base<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >::_M_is_engaged() const
  9. ......

Routes stream to specified buffer

Posted on by admin

Developer Command Prompt for VS 2019

  1. cl basic_ios_rdbuf.cpp /EHsc

MSDN Source Code

  1. #include <ios>
  2. #include <iostream>
  3. #include <fstream>
  4.  
  5. int main( ) 
  6. {
  7.    using namespace std;
  8.    ofstream file( "rdbuf.txt" );
  9.    streambuf *x = cout.rdbuf( file.rdbuf( ) );
  10.    cout << "test" << endl; // Goes to file
  11.    cout.rdbuf(x);
  12.    cout << "test2" << endl; //normal
  13. }