View source for cpp/language/range-for

===Explanation===
The above syntax produces code equivalent to the following {{rev inl|since=c++23| except for the lifetime expansion of temporaries of {{spar|range-initializer}} (see [[#Temporary range initializer|below]])}} (the variables and expressions wrapped in {{c/core|/* */}} are for exposition only):

{{rev begin}}
{{rev|until=c++17|
{{ttb|{}}<br>
:{{ttb|auto&&}} {{c/core|/* range */}} {{ttb|1==}} {{spar sep|range-initializer}}{{ttb|;}}<br>
:{{ttb|for (auto}} {{c/core|/* begin */}} {{ttb|1==}} {{c/core|/* begin-expr */}}{{ttb|,}} {{c/core|/* end */}} {{ttb|1==}} {{c/core|/* end-expr */}}{{ttb|;}}<br>
:::{{c/core|/* begin */}} {{ttb|1=!=}} {{c/core|/* end */}}{{ttb|; ++}}{{c/core|/* begin */}}{{ttb|)}}<br>
:{{ttb|{}}
::{{spar|item-declaration}} {{ttb|1== *}}{{c/core|/* begin */}}{{ttb|;}}<br>
::{{spar|statement}}<br>
:{{ttb|}<!---->}}<br>
{{ttb|}<!---->}}<br>
}}
{{rev|since=c++17|until=c++20|
{{ttb|{}}<br>
:{{ttb|auto&&}} {{c/core|/* range */}} {{ttb|1==}} {{spar sep|range-initializer}}{{ttb|;}}<br>
:{{ttb|auto}} {{c/core|/* begin */}} {{ttb|1==}} {{c/core|/* begin-expr */}}{{ttb|;}}<br>
:{{ttb|auto}} {{c/core|/* end */}} {{ttb|1==}} {{c/core|/* end-expr */}}{{ttb|;}}<br>
:{{ttb|for ( ;}} {{c/core|/* begin */}} {{ttb|1=!=}} {{c/core|/* end */}}{{ttb|; ++}}{{c/core|/* begin */}}{{ttb|)}}<br>
:{{ttb|{}}
::{{spar|item-declaration}} {{ttb|1== *}}{{c/core|/* begin */}}{{ttb|;}}<br>
::{{spar|statement}}<br>
:{{ttb|}<!---->}}<br>
{{ttb|}<!---->}}<br>
}}
{{rev|since=c++20|
{{ttb|{}}<br>
:{{spar|init-statement}}<br>
:{{ttb|auto&&}} {{c/core|/* range */}} {{ttb|1==}} {{spar sep|range-initializer}}{{ttb|;}}<br>
:{{ttb|auto}} {{c/core|/* begin */}} {{ttb|1==}} {{c/core|/* begin-expr */}}{{ttb|;}}<br>
:{{ttb|auto}} {{c/core|/* end */}} {{ttb|1==}} {{c/core|/* end-expr */}}{{ttb|;}}<br>
:{{ttb|for ( ;}} {{c/core|/* begin */}} {{ttb|1=!=}} {{c/core|/* end */}}{{ttb|; ++}}{{c/core|/* begin */}}{{ttb|)}}<br>
:{{ttb|{}}
::{{spar|item-declaration}} {{ttb|1== *}}{{c/core|/* begin */}}{{ttb|;}}<br>
::{{spar|statement}}<br>
:{{ttb|}<!---->}}<br>
{{ttb|}<!---->}}<br>
}}
{{rev end}}

{{spar|range-initializer}} is evaluated to initialize the sequence or range to iterate. Each element of the sequence, in turn, is dereferenced and is used to initialize the variable with the type and name given in {{spar|item-declaration}}.

{{spar|item-declaration}} can be one of the following:
* a {{rlpsd|declarations#Simple declaration}} with the following restrictions:
* It has only one {{rlp|declarations#Declarators|declarator}}.
* The declarator must have no {{rlp|initialization|initializer}}.
* The {{rlp|declarations#Specifiers|declaration specifier sequence}} can only contain type specifiers and {{c/core|constexpr}}, and it cannot define a {{rlp|class}} or {{rlp|enum|enumeration}}.

Exposition-only expressions {{c/core|/* begin-expr */}} and {{c/core|/* end-expr */}} are defined as follows:
* If the type of {{c/core|/* range */}} is a reference to an array type {{tt|R}}:
:* If {{tt|R}} is of bound {{c|N}}, {{c/core|/* begin-expr */}} is {{c|/* range */}} and {{c/core|/* end-expr */}} is {{c|/* range */ + N}}.
:* If {{tt|R}} is an array of unknown bound or an array of incomplete type, the program is ill-formed.
* If the type of {{c/core|/* range */}} is a reference to a class type {{tt|C}}, and searches in the scope of {{tt|C}} for the names “{{tt|begin}}” and “{{tt|end}}” each find at least one declaration, then {{c/core|/* begin-expr */}} is {{c|/* range */.begin()}} and {{c/core|/* end-expr */}} is {{c|/* range */.end()}}.
* Otherwise, {{c/core|/* begin-expr */}} is {{c|begin(/* range */)}} and {{c/core|/* end-expr */}} is {{c|end(/* range */)}}, where “{{tt|begin}}” and “{{tt|end}}” are found via {{rlp|adl|argument-dependent lookup}} (non-ADL lookup is not performed).

If the loop needs to be terminated within {{spar|statement}}, a {{rlp|break|{{c/core|break}} statement}} can be used as terminating statement.

If the current iteration needs to be terminated within {{spar|statement}}, a {{rlp|continue|{{c/core|continue}} statement}} can be used as shortcut.

If a name introduced in {{spar|init-statement}} is redeclared in the outermost block of {{spar|statement}}, the program is ill-formed:
{{source|1=
for (int i : {1, 2, 3})
    int i = 1; // error: redeclaration
}}