In article <Pine.PMDF.3.95.970913102712.587315117A-100000@WCUVAX1.WCU.EDU>, Carl Mummert <cm11214@WCUVAX1.WCU.EDU> wrote:
>I am curious about a behavior fo the vector class.
>
>What is the reasoning behind this not working:
>
>vector<int> vec(3);
>vec[5] = 2;  //not correct; operator[] won't
>             //allocate space

According to Stroustrup. the reason was efficiency (C++ PROGRAMMING LANGUAGE,
3rd Ed., section 16.3.3).  In order for vec[n] to automatically allocate
space, it would need to compare n to the current vector size every time vec[n]
is used.  In order to better match the speed of C arrays, it was decided that
vectors would not do range checking when the subscript operator was used.



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I am curious about a behavior fo the vector class.

What is the reasoning behind this not working:

vector<int> vec(3);
vec[5] = 2;  //not correct; operator[] won't
             //allocate space

The idea of vectors, after all, is that they be
self-defining and that they would automatically
allocate memory as needed.

But the standard (fairly clearly) indicates that
operator[] is only for access to the vector, and
that you must find other ways to insert new
objects past the end of the vector.

And yes, I do know I could use a map.  I don't
want to.  I just want to understand the reasoning
behind this behavior.

Thanks

Carl

--------------- cm11214@wcu.edu ---

One must imagine Sysiphus happy.
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