Getting the source behind clang's AST

Use the Lexer module:

clang::SourceManager *sm;
clang::LangOptions lopt;

std::string decl2str(clang::Decl *d) {
    clang::SourceLocation b(d->getLocStart()), _e(d->getLocEnd());
    clang::SourceLocation e(clang::Lexer::getLocForEndOfToken(_e, 0, *sm, lopt));
    return std::string(sm->getCharacterData(b),
        sm->getCharacterData(e)-sm->getCharacterData(b));
}

The following code works for me.

std::string decl2str(clang::Decl *d, SourceManager &sm) {
    // (T, U) => "T,,"
    string text = Lexer::getSourceText(CharSourceRange::getTokenRange(d->getSourceRange()), sm, LangOptions(), 0);
    if (text.size() > 0 && (text.at(text.size()-1) == ',')) //the text can be ""
        return Lexer::getSourceText(CharSourceRange::getCharRange(d->getSourceRange()), sm, LangOptions(), 0);
    return text;
}