trouble using lambda expressions and auto keyword in c++

Question

I'm trying to learn how to use lambda expressions in C++.

I tried this simple bit of code but I get compile errors:

int main()
{   
    vector<int> vec;
    for(int i = 1; i<10; i++)
    {
        vec.push_back(i);
    }
    for_each(vec.begin(),vec.end(),[](int n){cout << n << " ";});
    cout << endl;
}

Errors:

    forEachTests.cpp:20:61: error: no matching function for call to'for_each(std::vector<int>::iterator, std::vector<int>::iterator, main()::<lambda(int)>)'

    forEachTests.cpp:20:61: note: candidate is:
    c:\mingw\bin\../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_algo.h:4373:5: note:template<class _IIter, class _Funct> _Funct std::for_each(_IIter, _IIter, _Funct)

I also tried making the lambda expression an auto variable but I got a different set of errors.

Here is the code:

int main()
{   
    vector<int> vec;
    for(int i = 1; i<10; i++)
    {
        vec.push_back(i);
    }
    auto print = [](int n){cout << n << " ";};
    for_each(vec.begin(),vec.end(),print);
    cout << endl;
}

This gave me the following errors:

    forEachTests.cpp: In function 'int main()':

    forEachTests.cpp:20:7: error: 'print' does not name a type

    forEachTests.cpp:22:33: error: 'print' was not declared in this scope

I'm assuming these are problems with my compiler but I am not quite sure. I just installed MinGW and it appears to be using gcc 4.6.2.

Answer 1

You have to specify the standard option -std=c++0x (for gcc prior to version 4.7.0) or -std=c++11 (for gcc version 4.7.0 and later) when compiling the code under the new C++11 standard.