CODEWITHSUNDEEP
c++stringresize
Kiril Kirov
Kiril Kirov

Reputation: 38173

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

As the title says:

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

Of course, I can test it, but it could be UB, so testing will not work here.
In cppreference.com and cplusplus.com, the doc says nothing about this case

Example:

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

Upvotes: 1

Views: 413

Answers (2)

SingerOfTheFall
SingerOfTheFall

Reputation: 29966

ISO/IEC 14882:2011(E) § 21.4.4:

void resize(size_type n, charT c);

Requires: n <= max_size()

Throws: length_error if n > max_size().

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.

Upvotes: 1

Bo Persson
Bo Persson

Reputation: 92271

No, there are no guarantees. An implementation could reallocate the string to a new buffer, to reduce its capacity().

The standard says:

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.

Upvotes: 4

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