std::ranges:: cbegin

The return type models std::input_or_output_iterator and constant-iterator (since C++23) in all cases.

Customization point objects

The name ranges::cbegin denotes a customization point object , which is a const function object of a literal semiregular class type. For exposition purposes, the cv-unqualified version of its type is denoted as __cbegin_fn .

All instances of __cbegin_fn are equal. The effects of invoking different instances of type __cbegin_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, ranges::cbegin can be copied freely and its copies can be used interchangeably.

Given a set of types Args... , if std:: declval < Args > ( ) ... meet the requirements for arguments to ranges::cbegin above, __cbegin_fn models

• std:: invocable < __cbegin_fn, Args... > ,
• std:: invocable < const __cbegin_fn, Args... > ,
• std:: invocable < __cbegin_fn & , Args... > , and
• std:: invocable < const __cbegin_fn & , Args... > .
  

Otherwise, no function call operator of __cbegin_fn participates in overload resolution.

Notes

For an lvalue range e of type T , ranges :: cbegin ( e ) is equivalent to

Example

#include <cassert>
#include <ranges>
#include <vector>
 
int main()
{
    std::vector v{3, 1, 4};
    auto vi = std::ranges::cbegin(v);
    assert(3 == *vi);
    ++vi; // OK, constant-iterator object is mutable
    assert(1 == *vi);
    // *vi = 13; // Error: constant-iterator points to an immutable element
 
    int a[]{3, 1, 4};
    auto ai = std::ranges::cbegin(a); // cbegin works with C-arrays as well
    assert(3 == *ai and *(ai + 1) == 1);
    // *ai = 13; // Error: read-only variable is not assignable
}

See also