C++ iomanip Library - setw Function


The C++ function std::setw behaves as if member width were called with n as argument on the stream on which it is inserted/extracted as a manipulator (it can be inserted/extracted on input streams or output streams).

It is used to sets the field width to be used on output operations.


Following is the declaration for std::setw function.

setw (int n);


n − Number of characters to be used as field width.

Return Value

It returns unspecified. This function should only be used as a stream manipulator.


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

Data races

The stream object on which it is inserted/extracted is modified. Concurrent access to the same stream object may introduce data races.


In below example explains about setw function.

#include <iostream>
#include <iomanip>

int main () {
   std::cout << std::setw(10);
   std::cout << 77 << std::endl;
   return 0;

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