How to disable cout output in the runtime?

Question

I often use cout for debugging purpose in many different places in my code, and then I get frustrated and comment all of them manually.

Is there a way to suppress cout output in the runtime?

And more importantly, let's say I want to suppress all cout outputs, but I still want to see 1 specific output (let's say the final output of the program) in the terminal.

Is it possible to use an ""other way"" of printing to the terminal for showing the program output, and then when suppressing cout still see things that are printed using this ""other way""?

score 94 · Answer 1 · answered May 12 '15 at 08:03

Sure, you can (example here):

int main() {
    std::cout << "First message" << std::endl;

    std::cout.setstate(std::ios_base::failbit);
    std::cout << "Second message" << std::endl;

    std::cout.clear();
    std::cout << "Last message" << std::endl;

    return 0;
}

Outputs:

First message
Last message

This is because putting the stream in fail state will make it silently discard any output, until the failbit is cleared.

score 29 · Answer 2 · edited Aug 24 '16 at 14:33

29

To supress output, you can disconnect the underlying buffer from cout.

#include <iostream>

using namespace std;

int main(){

    // get underlying buffer
    streambuf* orig_buf = cout.rdbuf();

    // set null
    cout.rdbuf(NULL);

    cout << "this will not be displayed." << endl;

    // restore buffer
    cout.rdbuf(orig_buf);

    cout << "this will be dispalyed." << endl;

    return 0;
}

edited Aug 24 '16 at 14:33

Kijewski

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answered May 12 '15 at 10:59

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Does it have runtime overhead? – abhiarora Dec 04 '19 at 18:21

score 21 · Accepted Answer · answered May 12 '15 at 08:02

21

Don't use cout for debugging purposes, but define a different object (or function, or macro) that calls through to it, then you can disable that function or macro in one single place.

answered May 12 '15 at 08:02

RichieHindle

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ivan.mylyanyk · Answer 4 · 2016-11-03T09:33:14.920

5

You can user cerr - standard output stream for errors for your debug purposes.

Also, there is clog - standard output stream for logging.

Typically, they both behave like a cout.

Example:

cerr << 74 << endl;

Details: http://www.cplusplus.com/reference/iostream/cerr/

http://www.cplusplus.com/reference/iostream/clog/

edited Nov 03 '16 at 09:33

answered May 12 '15 at 08:02

ivan.mylyanyk

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score 1 · Answer 5 · answered Mar 05 '21 at 21:51

1

If you include files which involve cout you may want to write the code at the start (outside of main), which can be done like this:

struct Clearer {
    Clearer() { std::cout.setstate(std::ios::failbit); }
} output_clearer;

answered Mar 05 '21 at 21:51

Doot

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score 0 · Answer 6 · answered May 12 '15 at 08:04

It seems you print debug messages. You could use TRACE within Visual C++/MFC or you just might want to create a Debug() function which takes care of it. You can implement it to turn on only if a distinct flag is set. A lot of programs use a command line parameter called verbose or -v for instance, to control the behavior of their log and debug messages.

How to disable cout output in the runtime?

6 Answers6

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