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+[string.capacity]
+
+# 27 Strings library [[strings]](./#strings)
+
+## 27.4 String classes [[string.classes]](string.classes#string.capacity)
+
+### 27.4.3 Class template basic_string [[basic.string]](basic.string#string.capacity)
+
+#### 27.4.3.5 Capacity [string.capacity]
+
+[ð](#lib:size,basic_string)
+
+`constexpr size_type size() const noexcept;
+constexpr size_type length() const noexcept;
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2872)
+
+*Returns*: A count of the number of char-like objects currently in the string[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2876)
+
+*Complexity*: Constant time[.](#2.sentence-1)
+
+[ð](#lib:max_size,basic_string)
+
+`constexpr size_type max_size() const noexcept;
+`
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2887)
+
+*Returns*: The largest possible number of char-like objects that can be stored in abasic_string[.](#3.sentence-1)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2892)
+
+*Complexity*: Constant time[.](#4.sentence-1)
+
+[ð](#lib:resize,basic_string)
+
+`constexpr void resize(size_type n, charT c);
+`
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2903)
+
+*Effects*: Alters the value of*this as follows:
+
+- [(5.1)](#5.1)
+
+  Ifn <= size(),
+erases the last size() - n elements[.](#5.1.sentence-1)
+
+- [(5.2)](#5.2)
+
+  Ifn > size(),
+appends n - size() copies of c[.](#5.2.sentence-1)
+
+[ð](#lib:resize,basic_string_)
+
+`constexpr void resize(size_type n);
+`
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2926)
+
+*Effects*: Equivalent to resize(n, charT())[.](#6.sentence-1)
+
+[ð](#lib:resize_and_overwrite,basic_string)
+
+`template<class Operation> constexpr void resize_and_overwrite(size_type n, Operation op);
+`
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2937)
+
+Let
+
+- [(7.1)](#7.1)
+
+  o = size() before the call to resize_and_overwrite[.](#7.1.sentence-1)
+
+- [(7.2)](#7.2)
+
+  k be min(o, n)[.](#7.2.sentence-1)
+
+- [(7.3)](#7.3)
+
+  p be a value of type charT* or charT* const,
+such that the range [p, p + n] is valid andthis->compare(0, k, p, k) == 0 is true before the call[.](#7.3.sentence-1)
+  The values in the range [p + k, p + n] may be indeterminate ([[basic.indet]](basic.indet "6.8.5 Indeterminate and erroneous values"))[.](#7.3.sentence-2)
+
+- [(7.4)](#7.4)
+
+  m be a value of type size_type or const size_type equal to n[.](#7.4.sentence-1)
+
+- [(7.5)](#7.5)
+
+  *OP* be the expression std::move(op)(p, m)[.](#7.5.sentence-1)
+
+- [(7.6)](#7.6)
+
+  r = *OP*[.](#7.6.sentence-1)
+
+[8](#8)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2958)
+
+*Mandates*: *OP* has an integer-like type ([[iterator.concept.winc]](iterator.concept.winc "24.3.4.4 Concept weakly_incrementable"))[.](#8.sentence-1)
+
+[9](#9)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2962)
+
+*Preconditions*: 
+
+- [(9.1)](#9.1)
+
+  *OP* does not throw an exception or modify p or m[.](#9.1.sentence-1)
+
+- [(9.2)](#9.2)
+
+  r â¥ 0[.](#9.2.sentence-1)
+
+- [(9.3)](#9.3)
+
+  r â¤ m[.](#9.3.sentence-1)
+
+- [(9.4)](#9.4)
+
+  After evaluating *OP* there are no indeterminate values in the range [p, p + r)[.](#9.4.sentence-1)
+
+[10](#10)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2976)
+
+*Effects*: Evaluates *OP*,
+replaces the contents of *this with [p, p + r), and
+invalidates all pointers and references to the range [p, p + n][.](#10.sentence-1)
+
+[11](#11)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2982)
+
+*Recommended practice*: Implementations should avoid unnecessary copies and allocations
+by, for example, making p a pointer into internal storage and
+by restoring *(p + r) to charT() after evaluating *OP*[.](#11.sentence-1)
+
+[ð](#lib:capacity,basic_string)
+
+`constexpr size_type capacity() const noexcept;
+`
+
+[12](#12)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2995)
+
+*Returns*: The size of the allocated storage in the string[.](#12.sentence-1)
+
+[13](#13)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L2999)
+
+*Complexity*: Constant time[.](#13.sentence-1)
+
+[ð](#lib:reserve,basic_string)
+
+`constexpr void reserve(size_type res_arg);
+`
+
+[14](#14)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L3010)
+
+*Effects*: A directive that informs a basic_string of a planned change in size,
+so that the storage allocation can be managed accordingly[.](#14.sentence-1)
+
+Following a call toreserve,capacity() is greater or equal to the argument ofreserve if reallocation happens; and
+equal to the previous value ofcapacity() otherwise[.](#14.sentence-2)
+
+Reallocation happens at this point if and only if
+the current capacity is less than the argument of reserve[.](#14.sentence-3)
+
+[15](#15)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L3026)
+
+*Throws*: length_error ifres_arg > max_size() or any exceptions thrown byallocator_traits <Allocator>::allocate[.](#15.sentence-1)
+
+[ð](#lib:shrink_to_fit,basic_string)
+
+`constexpr void shrink_to_fit();
+`
+
+[16](#16)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L3040)
+
+*Effects*: shrink_to_fit is a non-binding request to reducecapacity() to size()[.](#16.sentence-1)
+
+[*Note [1](#note-1)*:
+
+The request is non-binding to
+allow latitude for implementation-specific optimizations[.](#16.sentence-2)
+
+â *end note*]
+
+It does not increase capacity(), but may reduce capacity() by causing reallocation[.](#16.sentence-3)
+
+[17](#17)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L3051)
+
+*Complexity*: If the size is not equal to the old capacity,
+linear in the size of the sequence;
+otherwise constant[.](#17.sentence-1)
+
+[18](#18)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L3057)
+
+*Remarks*: Reallocation invalidates all the references, pointers, and iterators
+referring to the elements in the sequence, as well as the past-the-end iterator[.](#18.sentence-1)
+
+[*Note [2](#note-2)*:
+
+If no reallocation happens, they remain valid[.](#18.sentence-2)
+
+â *end note*]
+
+[ð](#lib:clear,basic_string)
+
+`constexpr void clear() noexcept;
+`
+
+[19](#19)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L3072)
+
+*Effects*: Equivalent to: erase(begin(), end());
+
+[ð](#lib:empty,basic_string)
+
+`constexpr bool empty() const noexcept;
+`
+
+[20](#20)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/strings.tex#L3083)
+
+*Effects*: Equivalent to:return size() == 0;