Get parsing error code in clang::ParseAST

Question

I am facing a problem as follows:

• Given a source code in C. This source code may have some errors, such as undefined variable, undefined function.
• If the source code has an error, I need to point out which type and the location of that error. Otherwise, produce an AST.

I am using clang library to produce and traverse the AST, but I cannot get the error code if the source code has a compile error. When it runs to the folllowing command, it just outputs the error message on the screen:

clang::ParseAST(
     compilerInstance.getPreprocessor(), 
     &consumer, 
     compilerInstance.getASTContext()
);