Re: STL set container problem

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
9 May 2007 23:43:59 -0700
Message-ID:
<1178779439.534152.179990@y80g2000hsf.googlegroups.com>
Strnadel Josef wrote:

I have a following problem with set STL-container. I need to change
classB-members in some way (my below-mentioned iterator-access does not
work for the purpose)... Please try to help me where is my mistake if
messages...

problem.cc: In function `int main()':
problem.cc:50: error: assignment of data-member `B::i' in read-only
structure
problem.cc:51: error: passing `const std::set<C, std::less<C>,
std::allocator<C> >' as `this' argument of `void std::set<_Key, _Compare,
_Alloc>::clear() [with _Key = C, _Compare = std::less<C>, _Alloc =
std::allocator<C>]' discards qualifiers

...appear after compiling following c++ code (problem.cc) by
g++ problem.cc command:


What you're trying to do cannot possibly work. Members of a set
have a specific order; changing the value would require changing
the order, but you're doing it without the set knowing anything
about it. You can, of course, force the issue by means of
const_cast, but all that that buys you is that you end up
violating the invariants of std::set, which will cause problems
down the road.

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James Kanze (GABI Software) email:james.kanze@gmail.com
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