qmake error : could not find a Qt installation of '' - qt

Question

Error-
$ qmake
qmake: could not find a Qt installation of ''
I installed Qt Version 4.8.2
Partial File of .profile in my home directory
# set PATH so it includes user's private bin if it exists
if [ -d "$HOME/bin" ] ; then
PATH="$HOME/bin:$PATH"
PATH="/usr/local/Trolltech/Qt-4.8.2/bin:$PATH"
PATH="/home/user/qt-everywhere-opensource-src-4.8.2/bin:$PATH"
export PATH
fi
Output-
$ which qmake
/usr/bin/qmake
Properties
Name - qmake
Type - Link to executable (application/x-executable)
Link Target - qtchooser
Location - /usr/bin
qmake is present in this location
/usr/local/Trolltech/Qt-4.8.2/bin
Properties
Name - qmake
Type - executable (application/x-executable)
Size - 3.4 MB (3,407,312 bytes)
Location - /usr/local/Trolltech/Qt-4.8.2/bin
qmake is also present in this location
/home/username/qt-everywhere-opensource-src-4.8.2/bin
Properties
Name - qmake
Type - executable (application/x-executable)
Size - 11.2 MB (11,157,974 bytes)
Location - /home/username/qt-everywhere-opensource-src-4.8.2/bin
How to make qmake work? Which one is the correct path for qmake?

Answer 1

This is really simple. You don't need to modify any environmental variables, you don't need to set up QTDIR. There are only two facts you need to keep in mind:
You must invoke qmake from your desired version of Qt.
There's a 1:1 relationship between a particular installed Qt version and build, and qmake executable.
After the desired qmake was run and generated the makefile, invoking make will build your project using the version of Qt the qmake came from. This will happen in spite of any environmental variable settings etc.
So, all you need to know is which Qt installation you want to use, and its path. This should be obvious since you installed Qt yourself. There lies the bin/qmake that you need.
You can select the desired qmake just as you would select a particular binary to run. The process is not any different just because it is qmake and not, say gzip:
by explicitly typing out the path to the executable,
by using a shell alias,
by putting the desired Qt's bin folder onto the PATH.
Only you know where you installed your desired version of Qt - there are at least three paths in your question. Thus it's impossible to tell which qmake are you to invoke. Obviously one of them - the one picked up by which qmake - doesn't work.
You need to invoke the one that came with the version of Qt that you installed.
That's really all there's to it.

Answer 2

I think the source code is in this location:
/home/user/qt-everywhere-opensource-src-4.8.2/bin
and installation directory is at:
/usr/local/Trolltech/Qt-4.8.2/bin
you need to add the installation directory to your PATH, however if you have an other version (like the one in /usr/bin) you need to use /usr/local/Trolltech/Qt-4.8.2/bin/qmake to compile Qt project using this version.
My solution is to add this code to your .profile file:
export QTDIR="/usr/local/Trolltech/Qt-4.8.2"
export PATH="$QTDIR/bin:$PATH"
alias qmake-4.8="$QTDIR/bin/qmake"
after that use qmake-4.8 instead of qmake