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return statement

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Revision as of 19:06, 31 May 2013 by P12bot (Talk | contribs)

Terminates current function and returns specified value to the caller function.

Contents

Syntax

attr(optional) return expression(optional) ; (1)
attr(optional) return braced-init-list ; (2) (since C++11)
attr(C++11) - optional sequence of any number of attributes
expression - expression, convertible to the function return type
braced-init-list - brace-enclosed list of initializers and other braced-init-lists

Explanation

1) Evaluates the expression, terminates the current function and returns the result of the expression to the caller, after implicit conversion to the function return type. The expression is optional in functions whose return type is (possibly cv-qualified) void, in constructors and in destructors.
2) Uses copy-list-initialization to construct the return value of the function.

Notes

If control reaches the end of a function without encountering a return statement, return; is executed (except in the main function, where return 0; is executed).

Flowing off the end of a value-returning function (except main) without a return statement is undefined behavior.

In a function returning void, the return statement with expression can be used, if the expression type is void.

Returning by value may involve construction and copy/move of a temporary object, unless copy elision is used.

Keywords

return

Example

#include <iostream>
#include <string>
#include <utility>
 
void fa(int i)
{
    if (i == 2)
         return;
    std::cout << i << '\n';
} // implied return;
 
int fb(int i)
{
    if (i > 4)
         return 4;
    std::cout << i << '\n';
    return 2;
}
 
std::pair<std::string, int> fc(const char* p, int x)
{
    return {p, x};
}
 
void fd()
{
    return fa(10); // fa(10) is a void expression
}
 
int main()
{
    fa(2); // returns, does nothing when i==2
    fa(1); // prints its argument, then returns
    int i = fb(5); // prints its argument, returns 2
    i = fb(i); // prints its argument, returns 4
    std::cout << i << '\n'
              << fc("Hello", 7).second << '\n';;
    fd();
}

Output:

1
4
2
7
10