std::endl may cause an unnecessary flush

std::endl is used instead of the more efficient \n

Description

This defect flags uses of std::endl in I/O operations and allows you to use the more efficient alternative, \n.

Risk

std::endl inserts a newline (\n) followed by a flush operation. For instance:

std::cout << "Some content" << std::endl;

is equivalent to:

std::cout << "Some content" << '\n' << std::flush;

The implicit flush operation might not be necessary or intended. If your program has many I/O operations that use std::endl, the implicit flush operation can significantly reduce program performance. Since the flush operation is implicit, in case of a performance issue, it will be difficult to track the root cause of the issue.

Fix

Use \n to enter a newline wherever possible.

If you require a flush operation, instead of std::endl, use \n followed by an explicit flush operation, for instance:

std::cout << "Some content" << '\n' << std::flush;

In this case, the analysis considers your use of a flush operation as deliberate and does not flag the use.

Performance improvements might vary based on the compiler, library implementation, and environment that you are using.

Examples

Possible Performance Impact from std::endl Use

#include <fstream> 
using namespace std; 

int main() 
{ 
  ofstream aFile("file.txt"); 
  for ( int i = 0; i < 100000; i++) { 
    aFile << "Hello World " << std::endl ; 
  } 
  aFile.close();
  return 0; 
} 

In this example, an std::endl is used in a loop during a write operation on a file. Since the loop has 100000 iterations, the slight delay from each implicit flush operation can add up to a significant reduction of performance.

Use \n and Avoid Flush

In a loop with several iterations, avoid the performance reduction in I/O operations by using \n instead of std::endl.

#include <fstream> 
using namespace std; 

int main() 
{ 
  ofstream aFile("file.txt"); 
  for ( int i = 0; i < 100000; i++) { 
    aFile << "Hello World \n" ; 
  } 
  aFile.close(); 
  return 0; 
} 

Result Information

Group: Performance

Language: C++

Default: Off

Command-Line Syntax: STD_ENDL_USE

Impact: Low