Re: reference to a vector
struct bar {
double variable;
void init() { memset ( this, 0, sizeof ( bar ) ); }
bar() { init(); }
bool operator <( bar & f ) const
{ return ( variable > f.variable ) ; }
};
std::vector< bar >& run_it ()
{
std::vector< bar > *ptr_f = new std::vector<bar >;
bar f;
f.variable = 99.;
ptr_f->push_back ( f );
return ( *ptr_f );
}
// later
int main()
{
std::vector<bar > f = run_it();
std::cout << f.size() << std::endl;
std::cout << f[ 0 ].variable << std::endl;
}
For starters, the memset seems to make an assumption that bar is a pod
type and it's not,
The memory layout is most likely the same as a double so memsetting it
has the same effect of memsetting a double.
Agreed. It's horrible, and quite possibly UB.
I don't see it that way. I think it is just a simple matter made
complicated but the behavior is still well defined (but platform dependent.)
The definition could have been trivially the following:
struct bar {
double variable;
bar():variable(0.0){}
bool operator <( bar & f) const{
return variable > f.variable;
}
};
No, ptr_f is a pointer to memory allocated from the free store. The
memory doesn't go away when run_it() exits, and run_it returns a
reference to the vector allocated on the free store. The problem is
that the memory leaks -- there's no way to delete the new'ed vector.
I agree with you that the memory in OP's code is leaked. But it is
possible, though, to delete that memory. Simply
delete &f;
Regards,
Ben
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