std::string begin()/cbegin() method
- since C++20
- since C++11
- until C++11
// Nonconst version
constexpr iterator begin() noexcept;
// Const version
constexpr const_iterator begin() const noexcept;
constexpr const_iterator cbegin() const noexcept;
// Non const version
iterator begin() noexcept;
// Const version
const_iterator begin() const noexcept;
const_iterator cbegin() const noexcept;
// Non const version
iterator begin();
// Const version
const_iterator begin() const;
Returns an iterator
to the first element of the string.If the array is empty, the returned iterator will be equal to end()
.
Parameters
(none)
Return value
Iterator to the first element.
Complexity
Constant - O(1).
Notes
For a container c
, the expression *c.begin()
is equivalent to c.front()
.
Difference between begin and cbegin
For a const container c
, begin and cbegin are the same - c.begin() == c.cbegin()
For non-const container of type c
they return different iterators:
- Non const container
- Const container
- begin
- cbegin
#include <string>
int main()
{
std::string str = "Hello";
auto it = str.begin(); // Type: std::string::iterator
*it = 'J'; // ✔ Ok
}
#include <string>
int main()
{
std::string str = "Hello";
auto it = str.cbegin(); // Type: std::string::const_iterator
*it = 'J'; // ❌ Error!
}
- begin
- cbegin
#include <string>
int main()
{
const std::string str = "Hello";
auto it = str.begin(); // Type: std::string::const_iterator
*it = 'J'; // ❌ Error!
}
#include <string>
int main()
{
const std::string str = "Hello";
auto it = str.cbegin(); // Type: std::string::const_iterator
*it = 'J'; // ❌ Error!
}
Example
Main.cpp
#include <string>
#include <iostream>
int main()
{
std::string s("Exemplar");
*s.begin() = 'e';
std::cout << s <<'\n';
auto i = s.cbegin();
std::cout << *i << '\n';
// *i = 'E'; // error: i is a constant iterator
}
Output
exemplar
e
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