C++ ios Library - Function Left


It is used to sets the adjustfield format flag for the str stream to left. When adjustfield is set to left, the output is padded to the field width (width) by inserting fill characters (fill) at the end, effectively adjusting the field to the left.


Following is the declaration for std::left function.

ios_base& left (ios_base& str);


str − Stream object whose format flag is affected.

Return Value

It returns Argument str.


Basic guarantee − if an exception is thrown, str is in a valid state.

Data races

It modifies str. Concurrent access to the same stream object may cause data races.


In below example explains about std::left function.

#include <iostream>     

int main () {
   int n = -77;
   std::cout.width(6); std::cout << std::internal << n << '\n';
   std::cout.width(6); std::cout << std::left << n << '\n';
   std::cout.width(6); std::cout << std::right << n << '\n';
   return 0;

Let us compile and run the above program, this will produce the following result −

-   77