std::string size() method

od C++20

// Const version only
constexpr size_type size() const noexcept;

// Const version only
constexpr size_type length() const noexcept;

od C++11

// Const version only
size_type size() const noexcept;

// Const version only
size_type length() const noexcept;

do C++11

// Const version only
size_type size() const;

// Const version only
size_type length() const;

Returns the number of elements (CharTs) in the container, i.e. std::distance(begin(), end()).

Parameters

(none)

Return value

The number of elements (CharTs) in the container.

Complexity

od C++11

Constant - O(1).

do C++11

Unspecified.

Notes

For std::string, the elements are bytes (objects of type char), which are not the same as characters if a multibyte encoding such as UTF-8 is used.

Example

Main.cpp

#include <cassert>
#include <iterator>
#include <string>

int main()
{
    std::string s("Exemplar");
    assert(8 == s.size());
    assert(s.size() == s.length());
    assert(s.size() == static_cast<std::string::size_type>(
        std::distance(s.begin(), s.end())));

    std::u32string a(U"ハロー・ワールド"); // 8 code points
    assert(8 == a.size()); // 8 code units in UTF-32

    std::u16string b(u"ハロー・ワールド"); // 8 code points
    assert(8 == b.size()); // 8 code units in UTF-16

    std::string c("ハロー・ワールド"); // 8 code points
    assert(24 == c.size()); // 24 code units in UTF-8

    #if __cplusplus >= 202002
    std::u8string d(u8"ハロー・ワールド"); // 8 code points
    assert(24 == d.size()); // 24 code units in UTF-8
    #endif
}