c++ - 如果新尺寸与旧尺寸相同，标准是否保证 std::string::resize 不会做任何事情？

Question

正如标题所说:

Does the standard guarantee, that std::string::resize will not do anything, if the new size is the same as the old one?

_{当然可以测试，但可能是UB，所以这里测试不行。
在 cppreference.com 和 cplusplus.com 中，文档对这种情况只字未提}

例子:

std::string s( "asd" );
// s.size() is 3
s.resize( 3 );    // will this affect **somehow** the string?

Answer 1

不，没有任何保证。实现可以将字符串重新分配到新缓冲区，以减少其 capacity() .

标准说:

Effects: Alters the length of the string designated by *this as follows:

— If n <= size(), the function replaces the string designated by *this with a string of length n whose elements are a copy of the initial elements of the original string designated by *this.

— If n > size(), the function replaces the string designated by *this with a string of length n whose first size() elements are a copy of the original string designated by *this, and whose remaining elements are all initialized to c.