从控制台 C++ 中获取打印的语句

Question

I have two loggers in my program. One that I made inside a gui, and one that is super complicated but very well designed and prints to the console. I am trying to get the output from the nice console logger to the rendered one. I have tried everything under the sun to get this to work but I can't seem to figure it out (due to my lack of understanding of the code from the other logger(spdlog).) My conclusion is that taking the logs directly from what is printed is the best way to do this but I can't find online anyone asking how to do this. I have seen a few questions but they just post code as an answer and don't really explain what is going on. My question: Is there a way to grab printed statements from the console and what are the performance issues/complications that come with doing something like this.

For example, if i do std::cout << "hello!" << std::endl; std::cout << "hello!" << std::endl; or some printf statement, I want to be able to further down in the code be able to grab "hello!"

Answer 1

My conclusion is that taking the logs directly from what is printed is the best way to do this but I can't find online anyone asking how to do this.

Consoles nowadays are terminal emulators. The original terminals' output went to printers and couldn't be (easily) read back.

Application's stdout and stderr (console) streams are write-only. Moreover, in Windows and Unix/Linux you can pipe your program's (console) output (either or both stderr and stdout ) into another application with | (pipe) that creates a pipe IPC between stdout of your application and stdin of another one. That IPC pipe is write-only, your application cannot possibly read back from it.

You may be able to get access to the contents of the frame buffer of Windows cmd.exe that controls its Windows console window, but that won't be the verbatim byte-exact copy of data you wrote into stdout because of the escape sequences interpreted by Windows console .

If stdout is redirected into a file you can re-open that file for reading, but there is no portable way to re-open that file.

In other words, there is no portable way to read console output back.

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I have tried everything under the sun to get this to work but I can't seem to figure it out (due to my lack of understanding of the code from the other logger(spdlog).

I bet you haven't tried reading spdlog documentation, in particular logger with multi sinks . A sink is an output abstraction, which implementation can write into a file, memory or both. What you need is attach your own sink to spdlog that prints into your UI.

Derive your sink from base_sink and implement abstract member functions:

• virtual void sink_it_(const details::log_msg &msg) = 0; to print into the UI , and,
• virtual void flush_() = 0; to do nothing.

Then attach one object of your sink class to that spdlog .