在Qt 4.5.1中使用g ++的链接器错误

Question

I'm trying to test out a new dev environment and I am having some problems referencing some of the required Qt libraries.

First I ran this:

$ g++ HelloWorld.C -o HelloWorld -I /usr/local/Trolltech/Qt-4.5.1/include/QtCore/ -I /usr/local/Trolltech/Qt-4.5.1/include/

and got this error:

    /tmp/ccmsm4kZ.o: In function `QString::QString(char const*)':
HelloWorld.C:(.text._ZN7QStringC2EPKc[_ZN7QStringC5EPKc]+0x1d): undefined reference to `QString::fromAscii_helper(char const*, int)'
/tmp/ccmsm4kZ.o: In function `QString::~QString()':
HelloWorld.C:(.text._ZN7QStringD2Ev[_ZN7QStringD5Ev]+0x2d): undefined reference to `QString::free(QString::Data*)'
collect2: ld returned 1 exit status

So then I added reference to the QtCore library via:

$ g++ HelloWorld.C -o HelloWorld -I /usr/local/Trolltech/Qt-4.5.1/include/QtCore/ -I /usr/local/Trolltech/Qt-4.5.1/include/ -L /usr/local/Trolltech/Qt-4.5.1/lib -lQtCore

which removed the compile errors, however when I try to run the program I get this error:

./HelloWorld: error while loading shared libraries: libQtCore.so.4: cannot open shared object file: No such file or directory

I wasn't able to find a solution for this problem via google. Anyone have advice?

Answer 1

That error indicates that while the linker can find the library at compilation, it can't find it during runtime.

You should update your LD_LIBRARY_PATH to include that location like this:

In ~.bashrc probably somewhere near the bottom:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/Trolltech/Qt-4.5.1/lib

Alternatively, if you want to make this persistent throughout your system (and have root access), you can make an entry in /etc/ld.so.conf.d (on RedHat, I'm not sure about the other distributions)

touch /etc/ld.so.conf.d/qt.conf

Add the path to this file, and then update your runtime via /sbin/ldconfig