如何在运行时禁用 cout 输出？

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""?

Answer 1

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.

Answer 2

不要将cout用于调试目的，而是定义一个调用它的不同对象（或函数或宏），然后您可以在一个地方禁用该函数或宏。

Answer 3

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;
}

Answer 4

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/

Answer 5

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.

Answer 6

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;