Restore the state of std::cout after manipulating it.

Question

Hello Everyone,

Suppose I have a code like this:

void printHex(std::ostream& x){
    x<<std::hex<<123;
}
..
int main(){
    std::cout<<100; // prints 100 base 10
    printHex(std::cout); //prints 123 in hex
    std::cout<<73; //problem! prints 73 in hex..
}

My question is if there is any way to 'restore' the state of cout to its original one after returning from the function? (Somewhat like std::boolalpha and std::noboolalpha..) ?

Thanks, Iyer

Answer 1

The Boost IO Stream State Saver seems exactly what you need. :-)

Example based on your code snippet:

void printHex(std::ostream& x) {
    boost::io::ios_flags_saver ifs(x);
    x << std::hex << 123;
}

Answer 2

Googling gave me this:

  ios::fmtflags f;

  f = cout.flags(); // store flags

  cout.flags( f );

You'd probably want to put that at the head and end of your function.

Answer 3

With a little bit of modification to make the output more readable :

 void printHex(std::ostream& x){
     ios::fmtflags f(x.flags());
     x<<std::hex<<123<<"\n";
     x.flags(f);
  }


 int main(){
      std::cout<<100<<"\n"; // prints 100 base 10
      printHex(std::cout); //prints 123 in hex
      std::cout<<73<<"\n"; //problem! prints 73 in hex..
  }