Unable to force a clang CompilerInstance object to parse a header as C++ file

Question

I have a C++ header called class.h that I want to parse:

class MyClass
{
  public:
    Class() {}
    ~Class() {}
    bool isTrue() const;
    bool isFalse() const;
  private:
    bool m_attrib;
};

bool MyClass::isTrue() const
{
  return true;
}
bool MyClass::isFalse() const
{
  return false;
}

I use clang a compiler Instance with an AST consumer. All my code works well with c source file. But I am unable to configure/force the langage that the CompilerInstance must use. Here is the code I use :

m_ci = new clang::CompilerInstance();
/*configure the langage to use*/
clang::CompilerInvocation *invocation = new clang::CompilerInvocation;
clang::LangOptions langOpts;
/*with langage = clang::IK_CXX*/
langOpts.CPlusPlus = 1; 
invocation->setLangDefaults(langOpts, langage);
m_ci->setInvocation(invocation);
m_ci->createDiagnostics();
llvm::IntrusiveRefCntPtr<clang::TargetOptions> pto( new clang::TargetOptions());
pto->Triple = llvm::sys::getDefaultTargetTriple();
clang::TargetInfo *pti = clang::TargetInfo::CreateTargetInfo(m_ci->getDiagnostics(), pto.getPtr());
m_ci->setTarget(pti);
m_ci->createFileManager();
m_ci->createSourceManager(ci->getFileManager());
m_ci->createPreprocessor();
/*add some header search paths*/
m_hso = llvm::IntrusiveRefCntPtr<clang::HeaderSearchOptions>(new clang::HeaderSearchOptions());
m_hso->AddPath( pathName.c_str(),
                clang::frontend::Angled,
                false,
                false);
/*add the source file*/
const clang::FileEntry *pFile = m_ci->getFileManager().getFile(fileName.c_str());
m_ci->getSourceManager().createMainFileID(pFile);
/*parse*/
clang::InitializePreprocessor(m_ci->getPreprocessor(),
                              m_ci->getPreprocessorOpts(),
                              *m_hso,
                              m_ci->getFrontendOpts()); 
m_ci->createASTContext();
m_headerElements = new HeaderElements();
m_ci->setASTConsumer(m_headerElements);
m_ci->getDiagnosticClient().BeginSourceFile(m_ci->getLangOpts(),
                                            &m_ci->getPreprocessor());
clang::ParseAST(m_ci->getPreprocessor(), m_headerElements, m_ci->getASTContext());
m_ci->getDiagnosticClient().EndSourceFile();

When I test this, the parser throws errors like this:

error: unknown type name 'class'

And the test

 m_ci->getLangOpts.CPlusPlus == 0 

is true so it seems that the LangOptions is not applied on the CompilerInstance.

Answer 1

After some tests and a lot of searches, I have figured out how to do this. In order to set the Language Options of a CompilerInstance object, you just have to do this:

clang::CompilerInstance ci;
//initialize lot of stuff
ci.createDiagnostics();
ci.createFileManager();
ci.createSourceManager(m_ci.getFileManager());
std::shared_ptr<clang::TargetOptions> pto = std::make_shared<clang::TargetOptions>();
pto->Triple = llvm::sys::getDefaultTargetTriple();
clang::TargetInfo *pti = clang::TargetInfo::CreateTargetInfo(ci.getDiagnostics(), pto);
ci.setTarget(pti);
//force langage to C++
ci.getLangOpts().CPlusPlus = 1;
ci.createPreprocessor(clang::TU_Complete);

The important thing is to configure the LangOpts before creating or re-creating the preprocessor with CompilerInstance::createPreprocessor()