Abseil LOG output printed twice in Qt Creator

SandSnip3r

I have created a simple project which uses Abseil and is built and run inside of Qt Creator.

When I use any abseil logging, I see the output twice in the Qt Creator "Application Output" pane. Once in red and once again in white (I'm using dark theme). Using std::cout, I see the output once as white, as expected. Using std::cerr, I see the output once as red, as expected. I cannot figure out how to stop Abseil logging from printing twice. If I run the same process from the command line, the Abseil logs are only printed to stderr, as expected.

OS: Windows 10
Qt Creator versions tested: 11 & 12
Qt version: 6.2.4 MSVC2019 64bit

Abseil is recently cloned locally as a subdirectory. The commit is 2a636651729cec997a433ce8e363c6344130944e, though it happens with older versions too.

Here is the directory structure:

.
|-- CMakeLists.txt
|-- CMakeLists.txt.user
|-- abseil-cpp
`-- main.cpp

Here is my main:

#include <absl/log/globals.h>
#include <absl/log/initialize.h>
#include <absl/log/log.h>

#include <iostream>

int main() {
  absl::InitializeLog();
  absl::SetStderrThreshold(absl::LogSeverityAtLeast::kInfo);
  std::cout << "Cout test" << std::endl;
  std::cerr << "Cerr test" << std::endl;
  LOG(INFO) << "test";
  return 0;
}

This program will print something like:

Cout test
Cerr test
I0104 17:58:48.312991   20796 main.cpp:12] test
I0104 17:58:48.312991   20796 main.cpp:12] test

("Cerr test" and one of the "main.cpp:12] test" lines are red)

Here is my CMakeLists.txt:

cmake_minimum_required(VERSION 3.26.4)

project(main LANGUAGES CXX)

add_executable(${PROJECT_NAME}
  main.cpp
)

set(ABSL_PROPAGATE_CXX_STD ON)
add_subdirectory(abseil-cpp)

target_link_libraries(${PROJECT_NAME}
PUBLIC
  absl::log
  absl::log_initialize
)

Christian Ehrlicher

@SandSnip3r And it works correct when you run it from the command line? Please test.

SandSnip3r

@Christian-Ehrlicher Yes. From the command line, the output is as expected. No duplicates. See screenshots of Qt Creator and command line:

Christian Ehrlicher

Then try to not run it in the internal terminal - if it works there you should file a bug report.

SandSnip3r

@Christian-Ehrlicher I also tried it in the internal Qt Creator terminal. The output is as expected there.

Ok, I will file a bug. Thanks!

SandSnip3r

@SandSnip3r Done. https://bugreports.qt.io/browse/QTCREATORBUG-30163

SandSnip3r

It sounds like this is expected behavior. Abseil registers an additional "LogSink" for Windows' OutputDebugString, which is a different output stream than stdout or stderr.

Qt Creator displays this output type in the same place and style as stdout.

I think Qt Creator should not do this; or at least not do it so deceptively. I think one or both of these changes should be made:

Qt Creator should show this OutputDebugString in the Application Output window in a different color or in a separate pane
Qt Creator should allow you to disable this OutputDebugString

Thoughts?

Christian Ehrlicher

@SandSnip3r said in Abseil LOG output printed twice in Qt Creator:

Thoughts?

Feel free to add a patch for it - I doubt anyone else will do it for you since it's a rare usecase. Logging has to go to a log file, not stdout.