Question

I have the following code

#include <algorithm>
#include <iostream>
#include <vector>
#include <functional>


int main()
{
  typedef std::vector<int> Vector; 
  int sum=0;
  Vector v;
  for(int i=1;i<=10;++i)
     v.push_back(i);

  std::tr1::function<double()>  l=[&]()->double{

    std::for_each(v.begin(),v.end(),[&](int n){sum += n; //Error Here in MSVC++});
    return sum;
     };

  std::cout<<l();
  std::cin.get();
}

The above code produces an error on MSVC++ 10 whereas it compiles fine with g++ 4.5.
The error produced is 1 IntelliSense: invalid reference to an outer-scope local variable in a lambda body c:\users\super user\documents\visual studio 2010\projects\lambda\lambda.cpp 19 46 lambda


So, is there any other way to access the outer-scope variable sum without explicitly creating a new variable inside the local lambda expression(inside std::for_each)?

On g++ 4.5 the code compiles fine.
Does the standard(n3000 draft) say anything about it?(I don’t have a copy of C++-0x(1x ?) standard at present)

Answer 1

Have you actually tried compiling the code in the question? Visual C++ 2010 accepts the code, as is (with the comment removed, obviously), and successfully compiles the code without error.

The “error” you are seeing is not a compilation error, but an IntelliSense error. The IntelliSense error checking results in a lot of false positives (I’ve reported several bugs on Microsoft Connect over the past few months); in this case, IntelliSense is incorrectly saying this is an error when it is not.

You have two options: you can ignore the IntelliSense false positives or you can disable the IntelliSense error checking (right-click the Error List window and uncheck “Show IntelliSense Errors”).

Either way, these IntelliSense errors in no way prevent compilation from succeeding.