Use of uninitialised value of size 8

问题:

I'm having a quite strange problem with the fwd_iterator that I'm implementing:

if I use the iterators in methods defined inside the class, they work, but if I create a method with global scope in which I use iterators, valgrind says that I'm attempting to access to uninitialised memory.

It seems like iterators created outside the class cannot read a private attribute of the class (even with public methods created to do this).

This is the global-scope method:

template<typename T, class Pred>
int evaluate(SparseMatrix<T> &sm, Pred pred){
    typename SparseMatrix<T>:: iterator begin, end;
    int count=0;
    begin=sm.begin();
    end=sm.end();
    while(begin!=end){
            if(pred(*(begin->data))) count++;
            begin++;
    }
    int dcount=0;
    if(pred(sm.getDef())) dcount = ((sm.getRows() * sm.getCols()) - sm.getSize());
    return count+dcount;
}

This is the inside-class method:

void print_it() {
    iterator x=begin();
    iterator y=end();
    int i=1;
    while(x!=y){ 
        cout<<i<<".("<<(x->i)<<","<<(x->j)<<")="<<*(x->data)<<endl;
        ++x;
        i++;
    }
    if(x==y) cout<<"End."<<endl;
    cout<<endl;
}

Solved: iterator class has two attributes, value_type val, and sm, a pointer to the class itself. In operator=(const iterator& other) I forgot to add after val=other.val; the sm=other.sm; line.

Now everything works!

回答1:

iterator class has two attributes, value_type val, and sm, a pointer to the class itself. In operator=(const iterator& other) I forgot to add after val=other.val; the sm=other.sm; line.

Now everything works!