How to handle output of C++ redirected process

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C++

process

redirection

I am working on a C++ application and I am encountered a problem.

See below a brief description of my application :
There are two processes which work together. The main process (application A ) calls the second one (application B) which is the child of the first one.

Application A : Main application : C++ application with QT interface and a progress bar. It calls an another process with using CreateProcess.

Application B : C++ executable. This exe generates output messages on stdout like :
PROGRESS 1%
PROGRESS 20%
...
PROGRESS 100%

What I would like to do :
I would like to launch the application B with the application A. I mean when I launch the whole application, application A runs and creates another process which launchs the application B. I would like to catch the output of B and update the progress bar of application A.
I have implemented the redirected system explained on this article :
https://support.microsoft.com/en-us/kb/190351

It works but the problem is that the output messages of B are processed when the exe is terminated and not during the execution.
I would like to process the output messages of B during its execution. I was thinking to use the redirected system with using named pipes.
What do you think? Any advice ? any idea ?

Thank you in advance.