Re: [Boost-users] Re: dynamic boost::array and performance/size of STL vector

From: Victor A. Wagner Jr. (vawjr_at_[hidden])
Date: 2004-06-15 00:51:12

that's the answer on YOUR implementation...do NOT make assumptions about 
how all are implemented.

At Monday 2004-06-14 20:58, you wrote:
>Bo Peng wrote:
>
>I read /usr/include/c++/3.2.2/bits/stl_vector.h, here is the answer to my 
>own questions:
>
>>1. How is size() implemented in vector<>?
>
>end - start pointer. Not a reference to a variable. Too bad.
>
>>2.Since I will have a lot of such arrays, I would also like to know how 
>>many additional variables vector<int> keeps. I.e. exactly how big is 
>>vector<int> arr(5)?
>
>sizeof(int)*5 + sizeof(pointer)*3 since vector keeps three pointers: 
>start, end and end_of_storage. I am glad to find that when I initialize 
>vector with a parameter, there is no additional storage allocated. 
>arr.resize(5) of an empty array will not cause additional storage 
>allocation either.
>
>>It might be trivial to copy boost::array and add constructor/destructor 
>>but I do not want to re-invent the wheel.
>
>I am using typedef'ed vector now. I will use a modified boost::array later
>because I will be able to improve performance with a const size() and save
>some memory by using only one additional data member.
>
>Bo
>
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Victor A. Wagner Jr.      http://rudbek.com
The five most dangerous words in the English language:
               "There oughta be a law"