如何在Visual Studio 2013中写入输出窗口？

Question

I am able to compile and run my visual c++ program. It is not a console application. I am modifying an existing MFC application. I am trying to troubleshoot my program. I cannot run in debug and get the traces I need because my program also reads the mouse cursor. I also tried to use a messagebox to output this string, but again, a message box interferes with the mouse.

In the output window, I right-click and make sure that Program Output is enabled.

cout << "something" << endl;

However, in the output window, I do not see anything.

Looking at SO posts, I tried

std::string stro = "something ";
OutputDebugString(stro);

error C2664: 'void OutputDebugStringW(LPCWSTR)' : cannot convert argument 1 from 'std::string' to 'LPCWSTR'

So changed to std::wstring stro

and

OutputDebugString(stro.c_str());

to append an int, I had to

std::wostringstream wso;    
wso << i;   
stro = stro + wso.str();
OutputDebugString(stro.c_str());

But I cannot see output in the window when not running in DEBUG. Is there any way to see output in non-DEBUG? This is surprisingly frustrating.

In the comments, writing a separate overloaded class was suggested; this seems like overkill. Java has System.out.println even in GUI programs. Android has Log.v(). Such a pity the equivalent is not available here.

Answer 1

Console applications have console output, which is what cout sends to. Since this isn't a console application, you'll want to try another approach. It's strange you object "I don't see Debug output when I'm not in Debug", that's the point of it - don't use OutputDebugString and expect it to be for something other than debug output.

I think the best way to understand what your application is doing, without interacting with it under the debugger (I know the frustration of trying to debug event handlers that keep being re-triggered by your debugging activities) is to try tracepoints. I blogged about them back in 2006 and they're still a great technique. Reading the mouse cursor won't interfere with tracepoints, and you can turn them on and off without rebuilding your app or making any code changes.

Set up a breakpoint, then right-click the red dot and choose When Hit. You can adjust the default message that goes into the output window to show you any values you are interested in - you can even call functions in the trace message, as you can see in the blog entry where I call the size() method of a collection. If necessary, you can even debug a release build.

Answer 2

Actually OutputDebugStrng should work in release builds - as long as you're running the app from the debugger. However cout cannot route output to the VS output pane.

If you already have a lot of 'cout' style debugging code, the easiest route might be to replace it with a custom ostream overload which does print to the output pane. Here's one , here's another .

If you can rewrite the debugging code completely, some macro wrappers around OutputDebugString might be better for you.

Answer 3

Having a stdout/stderr console window for debugging is very useful, and I always miss it when working on WinMain based apps. I use this code fragment to create a console for windows apps (and chain it in with existing loggers, etc.) After running this, your cout/cerr should work fine. OutputDebugString output can be seen outside of DevStudio using the DebugView app, but I prefer this:

#include <io.h>
#include <fcntl.h>
...

//  DOS box console for stdin/stdout/stderr
void makeConsole()
{
    AllocConsole();

    HANDLE handle_out = GetStdHandle(STD_OUTPUT_HANDLE);
    int hCrt = _open_osfhandle((long)handle_out, _O_TEXT);
    FILE* hf_out = _fdopen(hCrt, "w");
    setvbuf(hf_out, NULL, _IONBF, 2);
    *stdout = *hf_out;

    HANDLE handle_in = GetStdHandle(STD_INPUT_HANDLE);
    hCrt = _open_osfhandle((long)handle_in, _O_TEXT);
    FILE* hf_in = _fdopen(hCrt, "r");
    setvbuf(hf_in, NULL, _IONBF, 2);
    *stdin = *hf_in;

    HANDLE handle_err = GetStdHandle(STD_ERROR_HANDLE);
    hCrt = _open_osfhandle((long)handle_err, _O_TEXT);
    FILE* hf_err = _fdopen(hCrt, "w");
    setvbuf(hf_err, NULL, _IONBF, 2);
    *stderr = *hf_err;

    ios::sync_with_stdio();
}