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# Range-based for loop (since C++11)

From cppreference.com
< cpp‎ | language

Executes a for loop over a range.

Used as a more readable equivalent to the traditional for loop operating over a range of values, such as all elements in a container.

### [edit] Syntax

attr(optional) `for (` range_declaration `:` range_expression `)` loop_statement |  |

### [edit] Explanation

The above syntax produces code similar to the following (`__range`, `__begin` and `__end` are for exposition only):

`{` `auto && __range =` range_expression `;` `for (auto __begin =` begin_expr`,` `__end =` end_expr`;` `__begin != __end; ++__begin) {` range_declaration `= *__begin;` loop_statement `}` `}` |  |

range_expression is evaluated to determine the sequence or range to iterate. Each element of the sequence, in turn, is dereferenced and assigned to the variable with the type and name given in range_declaration.

`begin_expr` and `end_expr` are defined as follows:

- If __range is an array, then `begin_expr` is __range and `end_expr` is (__range + __bound), where `__bound` is the number of elements in the array (if the array has unknown size or is of an incomplete type, the program is ill-formed)
- If __range's type is a class type with either or both a begin or an end member function, then `begin_expr` is `__range.begin()` and `end_expr` is `__range.end()`;
- Otherwise, `begin_expr` is begin(__range) and `end_expr` is end(__range), which are found via argument-dependent lookup (non-ADL lookup is not performed).

If range_expression returns a temporary, its lifetime is extended until the end of the loop, as indicated by binding to the rvalue reference `__range`, but beware that the lifetime of any temporary within range_expression is not extended.

Just as with a traditional loop, a break statement can be used to exit the loop early and a continue statement can be used to restart the loop with the next element.

attr represents an optional number of attributes.

### [edit] Keywords

`for`

### [edit] Example

Run this code

    #include <iostream>
    #include <vector>

    int main()
    {
        std::vector<int> v = {0, 1, 2, 3, 4, 5};

        for (int &i : v) // access by reference (const allowed)
            std::cout << i << ' ';

        std::cout << '\n';

        for (auto i : v) // compiler uses type inference to determine the right type
            std::cout << i << ' ';

        std::cout << '\n';

        for (int i : v) // access by value as well
            std::cout << i << ' ';

        std::cout << '\n';
    }

Output:

    0 1 2 3 4 5
    0 1 2 3 4 5
    0 1 2 3 4 5

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