Visual Studio 2019 hanging in cout/printf

Tyler 1

When debugging in Visual Studio 2019, any time my program attempts to cout or print it causes the debugger to stall infinitely. If I pause the debugger and look at the main thread, it will always be in 'ucrtbased.dll!write_text_ansi_nolock' once it gets stalled.

When I run the built exe on it's own, it prints to console perfectly fine. The stalling happens while the application is single threaded, just trying to console print out a single line of text with no variables.

How can I fix this, or look inside the above DLL to see what is happening?

David Lowndes 4,711 Reputation points

2021-10-10T18:23:23.977+00:00

Clearly this isn't normal behaviour, so do you have a small example that will allow someone to reproduce it?
RLWA32 40,651 Reputation points

2021-10-10T18:33:31.257+00:00

Also, what version of VS2019 are you using? Is it the latest one - 16.11.4?
Tyler 1 Reputation point

2021-10-11T02:26:37.467+00:00

I am using VS version 16.11.4, yes.

Reproduction is hard, because if I spin up a new hello world project, the behavior doesn't occur. With my current project the appearance of the problem seems to be inconsistent. Sometimes it happens and sometimes it doesn't even when the things I'm changing aren't related to printing. I could post the code if folks are curious but it is about 3 objects deep to be viable.

So is there a way to step into that dll, or any reference that will explain what 'write_text_ansi_nolock' is? Google isn't showing anything.
RLWA32 40,651 Reputation points

2021-10-11T08:03:46.3+00:00

VS2019 installed the source for the ucrt as part of the Windows SDK. In my VS2019 the function write_text_ansi_nolock is located in "C:\Program Files (x86)\Windows Kits\10\Source\10.0.19041.0\ucrt\lowio\write.cpp".

You can step into this function using the VS debugger with the following steps.

Disable "Just My Code" in debugging options -

Step into your application, open the ucrt source file and set a breakpoint in the write_text_ansi_nolock function. The VS debugger will show the breakpoint cannot be currently hit.

Go to the modules pane and select ucrtbased.dll

Right click and select "Load Symbols". The debugger should load the symbol file and the modules pane should change to -

The breakpoint should then change status and show that it will be hit when debugging continues.
Minxin Yu 10,031 Reputation points Microsoft Vendor

2021-10-11T08:35:42.433+00:00

Please check if there is a out of bounds problem in your program.

Tyler 1

Thanks, after installing the sdk and allowing the debugger to enter external not my code, I was able to catch where it was going. After changing some unrelated things, the problem is now back:

// hang is in ostream standard header - line 743
    if (!_Ok) {
        _State |= ios_base::badbit;
    } else { // state okay, insert
        _TRY_IO_BEGIN
        if ((_Ostr.flags() & ios_base::adjustfield) != ios_base::left) {
            for (; 0 < _Pad; --_Pad) { // pad on left
                if (_Traits::eq_int_type(_Traits::eof(), _Ostr.rdbuf()->sputc(_Ostr.fill()))) {
                    _State |= ios_base::badbit; // insertion failed, quit
                    break;
                }
            }
        }
    .//this is the next line to be executed when I pause the program
        if (_State == ios_base::goodbit && _Ostr.rdbuf()->sputn(_Val, _Count) != _Count) {
            _State |= ios_base::badbit;
        }

Tyler 1 Reputation point

2021-10-17T21:46:52.863+00:00

Why might an out of bounds cause soft lock failure in console output instead of throwing a straight out of bounds exception?
David Lowndes 4,711 Reputation points

2021-10-17T22:16:57.357+00:00

Because it may write somewhere that's not protected, but instead causes weird behaviour.
If you're not already, try building your debug build with the run-time checks (/RTC options) or AddressSanitizer (ASAN) enabled to see if they find any issues.
Also static analysis using the code analysis features in VS, or a 3'rd party tool such as the excellent PVS-Studio may find problems.
Minxin Yu 10,031 Reputation points Microsoft Vendor

2021-10-19T09:16:15.473+00:00

I am afraid it is hard to find out the error. It will be better to have a a minimal reproducible example to know what goes wrong.

6 answers

Octavi 0 Reputation points

2023-11-22T13:24:26.3933333+00:00

In my case, it got fixed by focusing on the cmd window and pressing space.

I guess (but I am not sure) that what happened was that I clicked on the cmd window and selected something by mistake; this usually freezes the application until you press a key and the selection disappears from the cmd window.

At least, I can reproduce it: just start debugging, click and drag on the cmd window (so something is selected), and then restart the debugger session. It will freeze in the WriteFile() of the write_text_ansi_nolock(). If you restart the debugging session (by pressing the stop button and play button in VS 2022), it freezes again at the same place. Once you focus on the cmd window and press a key, so the selection disappears, everything goes back to normal.

I am not sure that this is happening to anyone else, but at least it's something to try out.

I hope it helps someone :)
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