std::basic_string<CharT,Traits,Allocator>::resize_and_overwrite

 

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template< class Operation > constexpr void resize_and_overwrite( size_type count, Operation op );		(since C++23)

Resizes the string to contain at most count characters, using the user-provided operation op to modify the possibly indeterminate contents and set the length.

This function performs following steps:

1. Obtains a contiguous storage that contains count + 1 characters, and makes its first k character equal to the first k characters of *this, where k is the smaller of count and the result of this->size() before the call to resize_and_overwrite. Let p denote the pointer to the first character in the storage.
   • The equality is determined as if by checking this->compare(0, k, p, k) == 0.
   • The characters in [p + k, p + count] may have indeterminate values.
2. Evaluates std::move(op)(p, count). Let r be the return value of std::move(op)(p, count).
3. Replaces the contents of *this with [p, p + r) (which sets the length of *this to r). Invalidates all pointers and references to the range [p, p + count].

The program is ill-formed if r does not have an integer-like type. The behavior is undefined if std::move(op)(p, count) throws an exception or modifies p or count, r is not in the range [0, count], or any character in range [p, p + r) has an indeterminate value.

Implementations are recommended to avoid unnecessary copies and allocations by, e.g., making p equal to the pointer to beginning of storage of characters allocated for *this after the call, which can be identical to the existing storage of *this if count is less than or equal to this->capacity().

Parameters

count	-	the maximal possible new size of the string
op	-	the function object used for setting the new contents of the string

Return value

(none)

Exceptions

std::length_error if count > max_size(). Any exceptions thrown by corresponding Allocator.

If an exception is thrown from std::move(op)(p, count), the behavior is undefined. Otherwise, if an exception is thrown, this function has no effect.

Notes

resize_and_overwrite invalidates all iterators, pointers, and references into *this, regardless whether reallocation occurs. Implementations may assume that the contents of the string are not aliased after the call to resize_and_overwrite.

See also

resize	changes the number of characters stored (public member function)
make_uniquemake_unique_for_overwrite (C++14)(C++20)	creates a unique pointer that manages a new object (function template)
make_sharedmake_shared_for_overwrite (C++20)	creates a shared pointer that manages a new object (function template)
allocate_sharedallocate_shared_for_overwrite (C++20)	creates a shared pointer that manages a new object allocated using an allocator (function template)