Undefined reference to ...

Linux under programming appears undefined reference to ...

Cause Analysis:

1, the link is missing the relevant target file (. o)

2. The link is missing the relevant library file (. a/.so)

3. Another library file is used in the linked library file

4 Multiple library file link order issues

When you give the libraries you depend on in a link command, you need to be aware of the order of dependencies between libraries, and libraries that depend on other libraries must be placed in front of the dependent libraries, so that you can really avoid undefined reference errors and complete the compile link.

5. Linking C-language libraries in C + + code

Reference http://blog.csdn.net/aiwoziji13/article/details/7330333

Specific to the use of live555 static libraries in QT, you need to

LIBLIVEMEDIA.A libgroupsock.a libbasicusageenvironment.a LIBUSAGEENVIRONMENT.A copied to the compiled tree directory.
Then add the four library file order to the QT Creator Pro file, as

LIBS + = libgroupsock.a
LIBS + = Liblivemedia.a
LIBS + = Libbasicusageenvironment.a
LIBS + = Libusageenvironment.a

Undefined reference to ...