Re: assignment of const class members
On Dec 21, 3:38 am, hweek...@yahoo.com wrote:
hi,
it seems i can't assign the const variable u in class A, one way to
solve the problem may be to build a copy constructor. however, why
does C++ or vector class not like this code? my g++ is: gcc version
4.0.1 (Apple Inc. build 5465). thanks for the help.
summary of compile error:
---------------------------------------
cpp.C:4: error: non-static const member 'const unsigned int A::u',
can't use default assignment operator
/usr/include/c++/4.0.0/bits/vector.tcc:260: warning: synthesized
method 'A& A::operator=(const A&)' first required here
code:
-------
1
2 #include <vector>
3
4 struct A {
5 A(const unsigned int a) : u(a) { }
6 private: const unsigned int u;
7 };
8
9 int main () {
10
11 std::vector<A> y;
12 y.push_back(A(2));
13 }
[ snip ]
One of the requirements of containers such as std::vector is that its
elements be copyable and assigneable.
Your type has a const member, so default assignment fails (if you
think about it - thats safer and quite brilliant).
Solution: define your own op=(...) assuming that assigning that const
member is ok.
struct A
{
A(const unsigned a) : u(a) { }
A& operator=(const A& rhs)
{
if(&rhs == this) // self check!
return *this;
u = rhs.u;
return *this;
}
private:
unsigned u;
};