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std::span<T,Extent>::front

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< cpp‎ | container‎ | span

Compiler support

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Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

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Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

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Execution control library (C++26)

Technical specifications

External libraries

Containers library

(C++17)

(C++11)

(C++26)

(C++26)

(C++11)

Unordered associative

(C++11)

unordered_multiset

(C++11)

(C++11)

unordered_multimap

(C++11)

(C++23)

(C++23)

(C++23)

(C++23)

(C++20)

(C++23)

Tables

Iterator invalidation

Member function table

Non-member function table

Member functions

span::operator=

span::front

(C++26)

span::operator[]

span::beginspan::cbegin

(C++23)

span::endspan::cend

(C++23)

span::rbeginspan::crbegin

(C++23)

span::rendspan::crend

(C++23)

span::size_bytes

Non-member functions

as_bytesas_writable_bytes

Non-member constant

Deduction guides

constexpr reference front() const;

(since C++20)

Returns a reference to the first element in the span.

If empty() is true, the behavior is undefined.

(until C++26)

If empty() is true:

If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under "observe" evaluation semantic, the behavior is undefined.
If the implementation is not hardened, the behavior is undefined.

(since C++26)

Contents

[edit] Return value

A reference to the first element.

[edit] Complexity

Constant.

[edit] Notes

For a span c, the expression c.front() is equivalent to *c.begin().

[edit] Example

Run this code

#include <iostream>
#include <span>
 
void print(std::span <const int> const data)
{
 for (auto offset{0U}; offset != data.size(); ++offset)
 std::cout << data.subspan(offset).front() << ' ';
 std::cout << '\n';
}
 
int main()
{
 constexpr int data[]{0, 1, 2, 3, 4, 5, 6};
 print({data, 4});
}

Output:

0 1 2 3

[edit] See also

access the last element
(public member function) [edit]

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