C++ Manipulator boolalpha

C++ manipulator boolalpha function is used to set the output stream to display bool values as the strings "true" or "false"

Syntax

Parameter

str: stream object whose format flag is affected.

Return value

It returns argument str.

Data Races

Data races may be occurred when modified str concurrent accesses to the same stream object.

Exceptions

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

Example 1

Let's see the simple example to demonstrate the use of boolalpha:

#include <iostream>     // std::cout, std::boolalpha, std::noboolalpha

using namespace std;

int main () {
  bool b = true;
  cout <<"When we use boolalpha then b = " <<boolalpha << b << '\n';
  cout <<"When we use noboolalpha then b = " <<noboolalpha << b << '\n';
  return 0;
}

Output:

When we use boolalpha then b = true
When we use noboolalpha then b = 1

Example 2

Let's see another simple example:

#include <iostream>
using namespace std;
int main()
{
  bool b;
  b = true;
  
  cout<<"Output stream"<<endl<<"-------------"<<endl;
  cout << b << " " << boolalpha << b << endl;
  cout<<"\nInput stream"<<endl<<"--------------"<<endl;
  cout << "Enter a Boolean value: ";
  cin >> boolalpha >> b;
  cout << "Here is what you entered: " << b;
  return 0;
}

Output:

Output stream
-------------
1 true

Input stream
--------------
Enter a Boolean value: 0
Here is what you entered: false

Example 3

Let's see another simple example:

#include <sstream>
#include <locale>
#include <iostream>

using namespace std;

int main()
{
    // boolalpha output
    cout << boolalpha 
              << "boolalpha true: " << true << '\n'
              << "boolalpha false: " << false << '\n';
    cout << noboolalpha 
              << "noboolalpha true: " << true << '\n'
              << "noboolalpha false: " << false << '\n';
    // booalpha parse
    bool b1, b2;
    istringstream is("true false");
    is >> boolalpha >> b1 >> b2;
    cout << '\"' << is.str() << "\" parsed as " << b1 << ' ' << b2 << '\n';
    
return 0;
}

Output:

boolalpha true: true
boolalpha false: false
noboolalpha true: 1
noboolalpha false: 0
"true false" parsed as 1 0

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