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String move() and String(String &&rval) breaks operation of reserve()

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#161 4 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp
Domain
embedded-iot

Research direction

Locate the C++11 String implementation and inspect move(), operator=, the String(String &&rval) constructor, and reserve() behavior. Verify how a reserved destination behaves during a move, then confirm that the constructor follows the intended move path and that moved-from strings remain valid.

Written by the indexing model from the issue text.

Description

When #if __cplusplus >= 201103L || defined(GXX_EXPERIMENTAL_CXX0X)
operator = uses move() to just update the buffer pointer of the destination
This ignores any reserve() the user has made to ensure the memory is not unnecessarily fragmented.
String(String &&rval) has a similar problem

move() should first check the capacity of the destination and if there is sufficient space copy the source to the destination
String(String &&rval) should use move()

A suggested move() is

void String::move(String &rhs) {
	if (this != &rhs) {
           if (capacity > rhs.size) {
               copy(rhs.buffer,rhs.size);
             } else {
		free(buffer);
		buffer = rhs.buffer;
		len = rhs.len;
		capacity = rhs.capacity;
             }
		rhs.buffer = NULL;
		rhs.len = 0;
		rhs.capacity = 0;
	}
}
Dominant language
C++
Stars
306
Forks
150
No merged PRs in 30d

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