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Difference between revisions of "cpp/string/basic string/front"

From cppreference.com
< cpp‎ | string‎ | basic string
m (Text replace - "{{complex}}" to "===Complexity===")
m (→‎Synopsis: +constexpr since)
 
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{{cpp/string/basic_string/title | front}}
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{{cpp/string/basic_string/title|front}}
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{{cpp/string/basic_string/sidebar}}
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{{cpp/string/basic_string/navbar}}
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{{ddcl list begin}}
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{{dcl begin}}
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{{ddcl list item | notes={{mark c++0x}} |
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{{dcl|num=1|notes={{mark constexpr since c++20}}|
 
CharT& front();
 
CharT& front();
 
}}
 
}}
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{{ddcl list item | notes={{mark c++0x}} |
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{{dcl|num=2|notes={{mark constexpr since c++20}}|
 
const CharT& front() const;
 
const CharT& front() const;
 
}}
 
}}
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{{ddcl list end}}
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{{dcl end}}
  
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Returns reference to the first character in the string.  
+
Returns reference to the first character in the string. The behavior is undefined if {{lc|empty()}} is {{c/core|true}}.
  
 
===Parameters===
 
===Parameters===
−
{{param none}}
+
(none)
  
 
===Return value===
 
===Return value===
−
 
+
Reference to the first character, equivalent to {{c|operator[](0)}}.
−
reference to the first character.
+
  
 
===Complexity===
 
===Complexity===
−
{{complex constant}}
+
Constant.
 +
 
 +
===Notes===
 +
In libstdc++, {{tt|front()}} is [https://gcc.gnu.org/onlinedocs/libstdc++/manual/strings.html#strings.string.shrink not available] in C++98 mode.
 +
 
 +
===Example===
 +
{{example
 +
|code=
 +
#include <iostream>
 +
#include <string>
 +
 
 +
int main()
 +
{
 +
    std::string s("Exemplary");
 +
    char& f1 = s.front();
 +
    f1 = 'e';
 +
    std::cout << s << '\n'; // "exemplary"
 +
   
 +
    std::string const c("Exemplary");
 +
    char const& f2 = c.front();
 +
    std::cout << &f2 << '\n'; // "Exemplary"
 +
}
 +
|output=
 +
exemplary
 +
Exemplary
 +
}}
 +
 
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=534|std=C++98|before={{lc|std::basic_string}} did not have the member function {{tt|front()}}|after=added}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
 +
{{dsc begin}}
 +
{{dsc inc|cpp/string/basic_string/dsc back}}
 +
{{dsc inc|cpp/string/basic_string_view/dsc {{SUBPAGENAMEE}}}}
 +
{{dsc end}}
  
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{{dcl list begin}}
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{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
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{{dcl list template | cpp/string/basic_string/dcl list back}}
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{{dcl list end}}
+

Latest revision as of 05:43, 22 April 2024

 
C++
 
Strings library
 
std::basic_string
Member functions
(C++23)
Element access
basic_string::front
(DR*)
(DR*)
(C++17)
Iterators
(C++11)
(C++11)
(C++11)
(C++11)
Capacity
(DR*)
Modifiers
(C++23)
(DR*)
(C++23)
(C++23)
(C++23)  
Search
Operations
(C++20)
(C++20)
(C++23)
Constants
Non-member functions
(C++20)(C++20)
I/O
Comparison
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Numeric conversions
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)(C++11)
(C++11)
(C++11)
Literals
(C++14)
Helper classes
(C++11)
Deduction guides (C++17)

 
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. The behavior is undefined if empty() is true.

Contents

[edit] Parameters

(none)

[edit] Return value

Reference to the first character, equivalent to operator[](0).

[edit] Complexity

Constant.

[edit] Notes

In libstdc++, front() is not 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::string const c("Exemplary");
    char const& f2 = c.front();
    std::cout << &f2 << '\n'; // "Exemplary"
}

Output: 

exemplary
Exemplary

[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

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