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

 

C++

Compiler support

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Standard library

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Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

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Filesystem library(C++17)

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Symbols index

External libraries

 

Containers library

node-handle (C++17)

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

hive (C++26)

deque

forward_list (C++11)

list

Associative

set

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multimap

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unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

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flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

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std::span

Member functions

span::span

span::operator=

Element access

span::front

span::back

span::at (C++26)

span::operator[]

span::data

Iterators

span::beginspan::cbegin (C++23)

span::endspan::cend (C++23)

span::rbeginspan::crbegin (C++23)

span::rendspan::crend (C++23)

Observers

span::empty

span::size

span::size_bytes

Subviews

span::first

span::last

span::subspan

Non-member functions

as_bytesas_writable_bytes

Non-member constant

dynamic_extent

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)

Return value

A reference to the first element.

Complexity

Constant.

Notes

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

Example

Run this code

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

Output:

0 1 2 3

See also

back	access the last element (public member function)