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    <p><code>std::vector</code> is part of the STL, so any description of <code>std::vector</code> will do. The underlying implementation may differ slightly, but all conformant versions of STL must provide the same interface and the same guarantees for <code>std::vector</code>. I can't find in quickly on MSDN, but here are two such descriptions of <code>operator=</code>:</p> <ol> <li><a href="http://www.cplusplus.com/reference/stl/vector/operator=/" rel="nofollow noreferrer">http://www.cplusplus.com/reference/stl/vector/operator=/</a></li> <li><a href="http://www.sgi.com/tech/stl/Vector.html" rel="nofollow noreferrer">http://www.sgi.com/tech/stl/Vector.html</a></li> </ol> <p>Now, the second part of your question puzzles me. What would you expect <code>operator=</code> to do on a vector if not "copy everything from A into B"? </p> <p>In your example, your question was "how to make sure the old v get cleared?". I can interpret this in one of two ways: You might be asking "how do I know that this assignment <code>v = vector&lt;double&gt;(200,2)</code> will overwrite the contents of <code>v</code> and not append to it?". The answer is that you know that because that's the definition of how <code>operator=</code> works for STL containers. Any standards compliant implementation is guaranteed to work that way.</p> <p>You might also be asking "what happens to the contents of <code>v</code> when I overwrite them using the assignment <code>v = vector&lt;double&gt;(200,2)</code>?" The answer is that they are deallocated, and if they are objects, their destructors are called. Note the important distinction that if the vector contains <em>pointers to</em> objects, the pointers themselves are deallocated, but <em>not</em> what they point to.</p> <p>If I didn't answer your question, please try to clarify it.</p>
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    1. POWho can give me a link for the operator= of vector in MSDN?
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    1. USTyler McHenry
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    1. POWho can give me a link for the operator= of vector in MSDN?
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    1. COMy question is more like your second interpret. You said "The answer is that they are deallocated", but HOW if you just have a operator= COPYING every member in B.member to A.member without explicitly deallocating old A.member.
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    2. CO@8888: Who says it just copies every member?
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      1. USGManNickG
    3. COSo, what i am saying is that there should be a special operator= for vector doing the following thing: void operator=(vector& B) { erase elements in A resize A copy elements from B to A }
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