Using STDIN with an AllocConsole()

Question

I have a third-party dll that I load into software that isn't mine, and I'm using AllocConsole() to create the standard windows CLI window so I have an easy means of outputting debug messages.

My problem is though, is that it ignores any kind of input. I just want to be able to use the console I allocated and enable the ability for me to give it some input.

I'm assuming this is on MS Windows, since AllocConsole is a Microsoft API. Retagging appropriately. — Ben Voigt
– Ben Voigt, Commented Jan 26, 2012 at 16:00
It also says windows CLI in my post so no assumptions have to be made. Thanks for retag. — Nowayz
– Nowayz, Commented Jan 26, 2012 at 22:49

Nowayz · Accepted Answer · 2012-01-28 18:10:53Z

16

Thanks to Ben Voigt, I was able to cause the console to take input after I allocated it by doing:

freopen("CONIN$", "r", stdin); 
freopen("CONOUT$", "w", stdout); 
freopen("CONOUT$", "w", stderr);

This also directs the stdout and strerr to the same console window, in case they are directed someplace else for some reason.

answered Jan 28, 2012 at 18:10

Nowayz

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3 Comments

tmruss Over a year ago

In case it helps anyone, with VS2013 I was unable to get the console to close via FreeConsole without "putting back" stdout/stderr:freopen("OUT", "w", stdout);

Phi Over a year ago

freopen("NUL", "w", stdout) is better... "OUT" creates a file named "OUT" in current folder, whereas NUL is null output, so discards everything. CONOUT$ might be better still... not sure how that one works.

Andry Over a year ago

Beware of issues in freopen implementation of UCRT: 1. It does not reuse 0-2 descriptors, to reuse them you have to close them first: const int stdin_fileno = _fileno(stdin); fclose(stdin); if (stdin_fileno < 0) _close(STDIN_FILENO);. 2. In case of not console application (GUI) it will ignore SetStdHandle (_dup2 ignores it too), you have to excplicitly call it.

John M Cook · Accepted Answer · 2018-04-19 21:44:30Z

3

This is what I use.

    FILE *file = nullptr;
freopen_s(&file,"CONIN$", "r", stdin);
freopen_s(&file, "CONOUT$", "w", stdout);

Just hopes this helps someone.

answered Apr 19, 2018 at 21:44

John M Cook

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Comments

mkaes · Accepted Answer · 2012-01-26 15:50:30Z

2

Do you also redirect the stdoutand stderrto your console?

I used this code to get access to the JavaVM output from a Windows app.

if(::AllocConsole())
    {
        int hCrt = ::_open_osfhandle((intptr_t) ::GetStdHandle(STD_OUTPUT_HANDLE), _O_TEXT);
        FILE *hf = ::_fdopen( hCrt, "w" );
        *stdout = *hf;
        ::setvbuf(stdout, NULL, _IONBF, 0 );

        hCrt = ::_open_osfhandle((intptr_t) ::GetStdHandle(STD_ERROR_HANDLE), _O_TEXT);
        hf = ::_fdopen( hCrt, "w" );
        *stderr = *hf;
        ::setvbuf(stderr, NULL, _IONBF, 0 );
    }

After this I can see all stdoutand stderr outputs from the VM.

answered Jan 26, 2012 at 15:50

mkaes

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2 Comments

Nowayz Over a year ago

I've directed the stdout and stderr yes, but I still can't use the CLI window for STDIN. When I try to set the stdin correctly the window still refuses to be typed on.

Ben Voigt Over a year ago

The standard handles aren't associated with a console created after the program starts. If that were done first, the rest of this might work.

Ben Voigt · Accepted Answer · 2012-01-26 15:59:30Z

2

This is the code that works for me:

freopen("CONOUT$", "w", stdout);

You can probably do something similar with CONIN$ and stdin (Open for read, of course).

answered Jan 26, 2012 at 15:59

Ben Voigt

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