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Trimming Vector's Excess Capacity

 P: n/a I'm thinking of using "resize-to-size" to do the trimming: aVector.resize( aVector.size( ) ); I'm wondering why Scott Meyers was recommending "swap trick" instead, since the trick involves construction and destruction of a temporary, and might still leave some excess capacity in the vector. Apr 23 '06 #1
3 Replies

 P: n/a le******@yahoo.com wrote: I'm thinking of using "resize-to-size" to do the trimming: aVector.resize( aVector.size( ) ); I'm wondering why Scott Meyers was recommending "swap trick" instead, since the trick involves construction and destruction of a temporary, and might still leave some excess capacity in the vector. What problem are you trying to solve? -- Ian Collins. Apr 23 '06 #2

 P: n/a le******@yahoo.com wrote: I'm thinking of using "resize-to-size" to do the trimming: aVector.resize( aVector.size( ) ); I'm wondering why Scott Meyers was recommending "swap trick" instead, since the trick involves construction and destruction of a temporary, and might still leave some excess capacity in the vector. I'm lost. The code you posted just doesn't do anything (non-trivial.) A vector can reserve extra memory for future elements but resize wont release this memory. If you feel really like to get rid of the extra memory you can do a swap. To demonstrate you can try to compile the following program and run it: #include #include int main() { using std::vector; using std::cout; vector v(5); v.reserve(20); cout << "v.size() == " << v.size() << '\n' << "v.capacity() == " << v.capacity() << '\n'; // resize cout << "\nHere I do the vector resize.\n"; v.resize(v.size()); cout << "v.size() == " << v.size() << '\n' << "v.capacity() == " << v.capacity() << '\n'; // swap cout << "\nHere I do the vector swap.\n"; v.swap(vector(v)); cout << "v.size() == " << v.size() << '\n' << "v.capacity() == " << v.capacity() << '\n'; } Regards, Ben Apr 23 '06 #3

 P: n/a Duh on me. Resize-to-size does nothing on capacity. Thanks, benben, and Ian too. Regards, leeps_my Apr 23 '06 #4 