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

Revision as of 11:07, 31 July 2024

The class template basic_string stores and manipulates sequences of character-like objects, which are non-array objects of TrivialType and StandardLayoutType. The class is dependent neither on the character type nor on the nature of operations on that type. The definitions of the operations are supplied via the Traits template parameter - a specialization of std::char_traits or a compatible traits class.

The elements of a basic_string are stored contiguously, that is, for a basic_string s, &*(s.begin() + n) == &*s.begin() + n for any n in [​0​, s.size()), and *(s.begin() + s.size()) has value CharT() (a null terminator)(since C++11); or, equivalently, a pointer to s[0] can be passed to functions that expect a pointer to the first element of an array(until C++11)a null-terminated array(since C++11) of CharT.

std::basic_string satisfies the requirements of AllocatorAwareContainer (except that customized construct/destroy are not used for construction/destruction of elements), SequenceContainer and ContiguousContainer(since C++17).

If any of Traits::char_type and Allocator::char_type is different from CharT, the program is ill-formed.

Several typedefs for common character types are provided:

Template parameters

Member types

Member functions

Non-member functions

Literals

Helper classes

Deduction guides (since C++17)

Iterator invalidation

References, pointers, and iterators referring to the elements of a basic_string may be invalidated by any standard library function taking a reference to non-const basic_string as an argument, such as std::getline, std::swap, or operator>>, and by calling non-const member functions, except operator[], at, data, front, back, begin, rbegin, end, and rend.

Notes

Although it is required that customized construct or destroy is used when constructing or destroying elements of std::basic_string until C++23, all implementations only used the default mechanism. The requirement is corrected by P1072R10 to match existing practice.

Example

#include <iostream>
#include <string>
 
int main()
{
    using namespace std::literals;
 
    // Creating a string from const char*
    std::string str1 = "hello";
 
    // Creating a string using string literal
    auto str2 = "world"s;
 
    // Concatenating strings
    std::string str3 = str1 + " " + str2;
 
    // Print out the result
    std::cout << str3 << '\n';
 
    std::string::size_type pos = str3.find(" ");
    str1 = str3.substr(pos + 1); // the part after the space
    str2 = str3.substr(0, pos);  // the part till the space
 
    std::cout << str1 << ' ' << str2 << '\n';
 
    // Accessing an element using subscript operator[]
    std::cout << str1[0] << '\n';
    str1[0] = 'W';
    std::cout << str1 << '\n';
}

hello world
world hello
w
World

Defect reports

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

1. ↑ The Traits::char_type case is fixed in P1148R0.

See also

External links