title: clang tool : include path
body: <p>I would like to change my clang tool's include path according to input.
  When I run the below code on a sample test file I have a compilation error "header not found".</p>
  
  <pre><code>#include "clang/Frontend/FrontendActions.h"
  #include "clang/Tooling/CommonOptionsParser.h"
  #include "clang/Tooling/Tooling.h"
  // Declares llvm::cl::extrahelp.
  #include "llvm/Support/CommandLine.h"
  
  
  using namespace clang::tooling;
  using namespace llvm;
  
  static llvm::cl::OptionCategory MyToolCategory("my-tool options");
  
  
  int main(int argc , char** argv) {
      int argc_ = 5;
      const char **argv_ = new const char*[5];
      std::vector&lt;std::string&gt; Sources;
      Sources.push_back("path\\to\\Testfile.cpp");
      argv_[0] = argv[0];
      argv_[1] = &amp;Sources[0][0];
      argv_[2] = "--";
      argv_[3] = "c++";
      argv_[4] = "-I\"path\\to\\external\\lib\\directory\"";
      CommonOptionsParser OptionsParser(argc_, argv_, MyToolCategory);
      // run the Clang Tool, creating a new FrontendAction (explained below)
  
  
      ClangTool Tool(OptionsParser.getCompilations(), Sources);
      int result = Tool.run(newFrontendActionFactory&lt;clang::SyntaxOnlyAction&gt;().get());
  
      system("pause");
      return result;
  }
  </code></pre>