Your first code snippet is looking for a file at an absolute location (because of the leading '/') on the machine. I presume that location is not correct.

Your second code snippet changes the current working directory of the process, but this will have no effect if you continue to request a file with an absolute path.

Your third code snippet should find a file relative to the current working directory of the process (you could just use currentPath()), but is the current working directory where you think it is? If the file is installed and can be located relative to the executable then you should try: QCoreApplication::applicationDirPath() rather than relying on the current working directory.

If this file is a permanent part of your application then you should consider building it into the executable using the Qt resource system.