How to get output sent to stdout onto a string

Question

I have a function provided by a library (so I can't edit the source code for it), that prints output to stdout. I wish to get that output in a string variable, so that I can check some conditions on it. What is the best way to do this? Can I do it without multithreading and file I/O?

[EDIT] Similar questions(pointed out in comments):

Using multithreading:

Capture Output of Spawned Process to string

If you know output size beforehand:

redirect output from stdout to a string?

Are you trying to do this internal to your program, or do you just want to capture it from the terminal for a bash script? — tonysdg
– tonysdg, Commented Nov 13, 2015 at 20:24
You could redirect stdout to a file with something like this. stackoverflow.com/questions/14543443/… Definitely not the cleanest way but it would allow you to then open the file read it and compare. Should be able to jsut redirect to a pointer but I can't find that anywhere. — arduic
– arduic, Commented Nov 13, 2015 at 20:25
Did you try search stackoverflow first? This is duplicate of multiple. stackoverflow.com/questions/1162068/… stackoverflow.com/questions/14715493/… stackoverflow.com/questions/14428406/… stackoverflow.com/questions/11214498/… etc... — fukanchik
– fukanchik, Commented Nov 13, 2015 at 20:28
The cleanest approach which would catch everything is via pipe->dup2->fork — fukanchik
– fukanchik, Commented Nov 13, 2015 at 20:32

V. Kravchenko · Accepted Answer · 2015-11-13 20:28:53Z

1

Use rdbuf.

std::stringstream stream;
auto * old = std::cout.rdbuf(stream.rdbuf());
CallFunction();
std::cout.rdbuf(old);
std::string value = stream.str();

answered Nov 13, 2015 at 20:28

V. Kravchenko

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