std::basic_string<CharT,Traits,Allocator>::front

From cppreference.com

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

[edit]

Strings library

Classes
basic_string
basic_string_view (C++17)
char_traits

[edit]

std::basic_string

Member functions
basic_string::basic_string
basic_string::~basic_string
basic_string::operator=
basic_string::assign
basic_string::assign_range (C++23)
basic_string::get_allocator
Element access
basic_string::at
basic_string::operator[]
basic_string::front (DR*)
basic_string::back (DR*)
basic_string::data
basic_string::c_str
basic_string::operator basic_string_view (C++17)
Iterators
basic_string::beginbasic_string::cbegin (C++11)
basic_string::endbasic_string::cend (C++11)
basic_string::rbeginbasic_string::crbegin (C++11)
basic_string::rendbasic_string::crend (C++11)
Search
basic_string::find
basic_string::rfind
basic_string::find_first_of
basic_string::find_first_not_of
basic_string::find_last_of
basic_string::find_last_not_of

Modifiers
basic_string::clear
basic_string::insert
basic_string::insert_range (C++23)
basic_string::erase
basic_string::push_back
basic_string::pop_back (DR*)
basic_string::append
basic_string::append_range (C++23)
basic_string::operator+=
basic_string::replace
basic_string::replace_with_range (C++23)
basic_string::copy
basic_string::resize
basic_string::resize_and_overwrite (C++23)
basic_string::swap
Capacity
basic_string::empty
basic_string::sizebasic_string::length
basic_string::max_size
basic_string::reserve
basic_string::capacity
basic_string::shrink_to_fit (DR*)
Operations
basic_string::compare
basic_string::starts_with (C++20)
basic_string::ends_with (C++20)
basic_string::contains (C++23)
basic_string::substr

swap(std::basic_string)

erase(std::basic_string)erase_if(std::basic_string)

(C++20)(C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=>

(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Numeric conversions

stoistolstoll (C++11)(C++11)(C++11)
stoulstoull (C++11)(C++11)

stofstodstold (C++11)(C++11)(C++11)
to_string (C++11)
to_wstring (C++11)

Literals

operator""s

(C++14)

Helper classes

hash<std::basic_string>

(C++11)

Deduction guides(C++17)

[edit]

CharT& front();	(1)	(constexpr since C++20)
const CharT& front()const;	(2)	(constexpr since C++20)

Returns reference to the first character in the string.

Ifempty() istrue, the behavior is undefined.

(until C++26)

Ifempty() istrue:

If the implementation ishardened, acontract 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)

[edit]Return value

operator[](0)

[edit]Complexity

Constant.

[edit]Notes

In libstdc++,front() isnot available in C++98 mode.

[edit]Example

Run this code

#include <iostream>#include <string> int main(){std::string s("Exemplary");char& f1= s.front();    f1='e';std::cout<< s<<'\n';// "exemplary" std::stringconst c("Exemplary");charconst& f2= c.front();std::cout<<&f2<<'\n';// "Exemplary"}

Output:

exemplaryExemplary

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 534	C++98	std::basic_string did not have the member function`front()`	added

[edit]See also

back (DR*)	accesses the last character (public member function)[edit]
front	accesses the first character (public member function of`std::basic_string_view<CharT,Traits>`)[edit]