std::basic_string<CharT,Traits,Allocator>::basic_string - cppreference.com (original) (raw)

Constructs new string from a variety of data sources and optionally using user supplied allocator alloc.

1. The default constructor since C++11. Constructs an empty string with a default-constructed allocator.

2. The default constructor until C++11. Constructs an empty string with the given allocator alloc.

3. Constructs a string with count copies of character ch.

1. Constructs a string with the contents of the range [first, last). Each iterator in [first, last) is dereferenced exactly once.

1. Constructs a string with the contents of the range rg. Each iterator in rg is dereferenced exactly once.

2. Constructs a string with the contents of the range [s, s + count).

If [s, s + count) is not a valid range, the behavior is undefined.

1. Equivalent to basic_string(s, Traits::length(s), alloc).

1. std::basic_string cannot be constructed from nullptr.

2. Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then constructs a string as if by basic_string(sv.data(), sv.size(), alloc).

3. Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then constructs a string as if by basic_string(sv.substr(pos, n), alloc).

11-18) Constructs a string with (part of) the contents of other. If the type of other is basic_string&&, when the construction finishes, other is in a valid but unspecified state.

1. The copy constructor.

1. The move constructor. The allocator is obtained by move construction from other.get_allocator().

2. Same as the copy constructor, except that alloc is used as the allocator.

3. Same as the move constructor, except that alloc is used as the allocator.

15,16) Constructs a string with the contents of the range [other.data() + pos, other.data() + other.size()).

17,18) Constructs a string with the contents of the range [other.data() + pos, other.data() + (pos + std::min(count, other.size() - pos))).

1. Equivalent to basic_string(ilist.begin(), ilist.end()).

Contents

• 1 Parameters
• 2 Complexity
• 3 Exceptions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[edit] Complexity

1,2) Constant.

3-7) Linear in the size of the string.

9-11) Linear in the size of the string.

1. Constant.

2. Linear in the size of the string.

3. Linear in the size of the string if alloc != other.get_allocator() is true, otherwise constant.

15-19) Linear in the size of the string.

[edit] Exceptions

1. Throws nothing if alloc == str.get_allocator() is true.

Throws std::length_error if the length of the constructed string would exceed max_size() (for example, if count > max_size() for (3)). Calls to Allocator::allocate may throw.

If an exception is thrown for any reason, these functions have no effect (strong exception safety guarantee).

[edit] Notes

Initialization with a string literal that contains embedded '\0' characters uses the overload (7), which stops at the first null character. This can be avoided by specifying a different constructor or by using [operator""s](operator%2522%2522s.html "cpp/string/basic string/operator""s"):

[edit] Example

#include #include #include #include #include #include   int main() { std::cout << "1) string(); "; std::string s1; assert(s1.empty() && (s1.length() == 0) && (s1.size() == 0)); std::cout << "s1.capacity(): " << s1.capacity() << '\n'; // unspecified   std::cout << "3) string(size_type count, CharT ch): "; std::string s2(4, '='); std::cout << std::quoted(s2) << '\n'; // "===="   std::cout << "4) string(InputIt first, InputIt last): "; char mutable_c_str[] = "another C-style string"; std::string s4(std::begin(mutable_c_str) + 8, std::end(mutable_c_str) - 1); std::cout << std::quoted(s4) << '\n'; // "C-style string"   std::cout << "6) string(CharT const* s, size_type count): "; std::string s6("C-style string", 7); std::cout << std::quoted(s6) << '\n'; // "C-style", i.e. [0, 7)   std::cout << "7) string(CharT const* s): "; std::string s7("C-style\0string"); std::cout << std::quoted(s7) << '\n'; // "C-style"   std::cout << "11) string(string&): "; std::string const other11("Exemplar"); std::string s11(other11); std::cout << std::quoted(s11) << '\n'; // "Exemplar"   std::cout << "12) string(string&&): "; std::string s12(std::string("C++ by ") + std::string("example")); std::cout << std::quoted(s12) << '\n'; // "C++ by example"   std::cout << "15) string(const string& other, size_type pos): "; std::string const other15("Mutatis Mutandis"); std::string s15(other15, 8); std::cout << std::quoted(s15) << '\n'; // "Mutandis", i.e. [8, 16)   std::cout << "17) string(const string& other, size_type pos, size_type count): "; std::string const other17("Exemplary"); std::string s17(other17, 0, other17.length() - 1); std::cout << std::quoted(s17) << '\n'; // "Exemplar"   std::cout << "19) string(std::initializer_list): "; std::string s19({'C', '-', 's', 't', 'y', 'l', 'e'}); std::cout << std::quoted(s19) << '\n'; // "C-style" }

Possible output:

1. string(); s1.capacity(): 15
2. string(size_type count, CharT ch): "===="
3. string(InputIt first, InputIt last): "C-style string"
4. string(CharT const* s, size_type count): "C-style"
5. string(CharT const* s): "C-style"
6. string(string&): "Exemplar"
7. string(string&&): "C++ by example"
8. string(const string& other, size_type pos): "Mutandis"
9. string(const string& other, size_type pos, size_type count): "Exemplar"
10. string(std::initializer_list): "C-style"

[edit] Defect reports

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

1. ↑ [nullptr, nullptr + 0) is a valid empty range, because adding zero to a null pointer value is also well-defined (the result is still a null pointer value).

[edit] See also

| | assign characters to a string (public member function) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | assigns values to the string (public member function) [edit] | | | converts an integral or floating-point value to string (function) [edit] | | | converts an integral or floating-point value to wstring (function) [edit] | | | constructs a basic_string_view (public member function of std::basic_string_view<CharT,Traits>) [edit] |