21 Strings library [strings]

21.3 String classes [string.classes]

21.3.2 Class template basic_­string [basic.string]

21.3.2.4 Capacity [string.capacity]

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constexpr size_type size() const noexcept; constexpr size_type length() const noexcept;
1
#
Returns: A count of the number of char-like objects currently in the string.
2
#
Complexity: Constant time.
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constexpr size_type max_size() const noexcept;
3
#
Returns: The largest possible number of char-like objects that can be stored in a basic_­string.
4
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Complexity: Constant time.
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constexpr void resize(size_type n, charT c);
5
#
Effects: Alters the value of *this as follows:
  • (5.1)
    If n <= size(), erases the last size() - n elements.
  • (5.2)
    If n > size(), appends n - size() copies of c.
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constexpr void resize(size_type n);
6
#
Effects: Equivalent to resize(n, charT()).
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constexpr size_type capacity() const noexcept;
7
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Returns: The size of the allocated storage in the string.
8
#
Complexity: Constant time.
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constexpr void reserve(size_type res_arg);
9
#
Effects: A directive that informs a basic_­string of a planned change in size, so that the storage allocation can be managed accordingly.
After reserve(), capacity() is greater or equal to the argument of reserve if reallocation happens; and equal to the previous value of capacity() otherwise.
Reallocation happens at this point if and only if the current capacity is less than the argument of reserve().
10
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Throws: length_­error if res_­arg > max_­size() or any exceptions thrown by allocator_­traits <Allocator>​::​allocate.
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constexpr void shrink_to_fit();
11
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Effects: shrink_­to_­fit is a non-binding request to reduce capacity() to size().
[Note
:
The request is non-binding to allow latitude for implementation-specific optimizations.
— end note
]
It does not increase capacity(), but may reduce capacity() by causing reallocation.
12
#
Complexity: If the size is not equal to the old capacity, linear in the size of the sequence; otherwise constant.
13
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Remarks: Reallocation invalidates all the references, pointers, and iterators referring to the elements in the sequence, as well as the past-the-end iterator.
[Note
:
If no reallocation happens, they remain valid.
— end note
]
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constexpr void clear() noexcept;
14
#
Effects: Equivalent to: erase(begin(), end());
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[[nodiscard]] constexpr bool empty() const noexcept;
15
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Effects: Equivalent to: return size() == 0;