Error reporting information:
first of all, it is necessary to distinguish the two types of error : undefined reference to xxxxx
and "XXXX was not declared in this scope"
. The former is because the compiler can find the declaration of the function, but cannot find the definition of the function, so it reports an error; The latter is not found at all. You should first check whether the header file is missing.
For undefined reference to xxxxx
, there are two situations at present
1. The path to ffmpeg in the pro file is not correct
2. The header file is written in C, but without extern "C" {}