C++ - How to reset the output stream manipulator flags [duplicate]

问题

I've got a line of code that sets the fill value to a '-' character in my output, but need to reset the setfill flag to its default whitespace character. How do I do that?

cout << setw(14) << "  CHARGE/ROOM" << endl;
cout << setfill('-') << setw(11) << '-' << "  " << setw(15) << '-' << "   " << setw(11) << '-' << endl;

I thought this might work:

cout.unsetf(ios::manipulatorname) // Howerver I dont see a manipulator called setfill

Am I on the wrong track?

回答1:

Have a look at the Boost.IO_State_Savers, providing RAII-style scope guards for the flags of an iostream.

Example:

#include <boost/io/ios_state.hpp>

{
  boost::io::ios_all_saver guard(cout); // Saves current flags and format

  cout << setw(14) << "  CHARGE/ROOM" << endl;
  cout << setfill('-') << setw(11) << '-' << "  " << setw(15) << '-' << "   " << setw(11) << '-' << endl;
// dtor of guard here restores flags and formats
}

More specialized guards (for only fill, or width, or precision, etc... are also in the library. See the docs for details.

回答2:

You can use copyfmt to save cout's initial formatting. Once finished with formatted output you can use it again to restore the default settings (including fill character).

{
    // save default formatting
    ios init(NULL);
    init.copyfmt(cout);

    // change formatting...
    cout << setfill('-') << setw(11) << '-' << "  ";
    cout << setw(15) << '-' << "   ";
    cout << setw(11) << '-' << endl;

    // restore default formatting
    cout.copyfmt(init);
}

回答3:

You can use the ios::fill() function to set and restore the fill character instead.

http://www.cplusplus.com/reference/iostream/ios/fill/

#include <iostream>
using namespace std;

int main () {
  char prev;

  cout.width (10);
  cout << 40 << endl;

  prev = cout.fill ('x');
  cout.width (10);
  cout << 40 << endl;

  cout.fill(prev);

  return 0;
}

回答4:

You can manually change the setfill flag to whatever you need it to be:

float number = 4.5;
cout << setfill('-');
cout << setw(11) << number << endl; // --------4.5
cout << setfill(' ');
cout << setw(11) << number << endl; // 4.5

回答5:

The null character will reset it back to the original state: setfill('\0')

来源：https://stackoverflow.com/questions/1513625/c-how-to-reset-the-output-stream-manipulator-flags

标签

c++

manipulators