return is a keyword that ends a function (or member function). Depending on the function, return might return anything or nothing.

The following function calculates the square of an integer:


///Calculates the square of an integer

int Square(const int x)

{

  const int solution = x * x;

  return solution;

}

If a function returns nothing (that is, a return type of void), one can omit the final return:


#include <iostream>



void SayHello()

{

  std::cout << "Hello\n";

  //return; //No need to return from a void function

}

Exception: main

The function main is special. It returns an integer error code of the program, where a zero denotes a no-failure run. When main's closing bracket is reached, the effect is equivalent to (Standard, 3.6.1.5):


return 0;

Therefore, the following two pieces of code are equivalent:


int main() {}


int main() { return 0; }

return in a C++11 lambda expression

Download the Qt Creator project 'CppLambdaExpression' (zip)

Program flow in a C++11 lambda expression differs from a C++98 lambda expression or BOOST_FOREACH: if you want to return from a function, all that happens is that the std::for_each (or other algorithm) is terminated. The example below shows this.


#include <algorithm>

#include <cassert>

#include <iostream>

#include <vector>



void TestProgramFlow()

{

  //2-D std::vector, note 42 in the middle, from an initializer list

  const std::vector<std::vector<int> > v

    =

    {

      {  0, 1, 2, 3, 4 },

      { 10,11,12,13,14 },

      { 40,41,42,43,44 },

      { 50,51,52,53,54 },

      { 60,61,62,63,64 }

    };

  //First lambda expression

  std::for_each(v.begin(),v.end(),

    [](const std::vector<int>& w)

    {

      //Nested second lambda expression

      std::for_each(w.begin(),w.end(),

        [](const int i)

        {

          if (i == 42)

          {

            std::cout << "FOUND!\n";

            return; //Terminates the second lambda expression,

                    //Does not return from Test function

          }

        }

      );

    }

  );

  //Will get here, as the return statement only terminates

  //the second lambda expression, instead of the Test function

  assert(!"Should not get here");

}

Screen output:


FOUND!

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.

(C++) return

Exception: main

return in a C++11 lambda expression