It's not clear at all to me what you try to do.
However, bear in mind that the C++ domain has nothing to do with the bash domain, and that you MUST abide the correct syntax for each one when you are using it.
The fact that you are calling bash from within a QT program is irrelevant, the bash script needs to abide the bash syntax. And in bash you never do something like "system()", because simply bash doesn't work that way. Bash is a command interpreter by itself, it doesn't need to do a system() call to launch a program, and it can't call a qt or c++ function either.
I assume that "system-config-network" is a command line tool. Isn't it? What does the script do that you can't code in C++ directly? Calling an additional shell instance might be an overkill.