I'm a C++ beginner, many questions around me. I have defined !=
operator of int_node
, but when I compile this code, show error:
invalid operands to binary expression ('int_node' and const 'int_node')
The IDE that I use is xcode 4.6.
Below is my all code
typedef struct int_node{
int val;
struct int_node *next;
} int_t;
template <typename Node>
struct node_wrap{
Node *ptr;
node_wrap(Node *p = 0) : ptr(p){}
Node &operator *() const {return *ptr;}
Node *operator->() const {return ptr;}
node_wrap &operator++() {ptr = ptr->next; return *this;}
node_wrap operator++(int) {node_wrap tmp = *this; ++*this; return tmp;}
bool operator == (const node_wrap &i) const {return ptr == i.ptr;}
bool operator != (const node_wrap &i) const {return ptr != i.ptr;}
} ;
template <typename Iterator, typename T>
Iterator find(Iterator first, Iterator last, const T& value)
{
while (first != last && *first != value) // invalid operands to binary experssion ('int_node' and const 'int_node')
{
++first;
return first;
}
}
int main(int argc, const char * argv[])
{
struct int_node *list_head = nullptr;
struct int_node *list_foot = nullptr;
struct int_node valf;
valf.val = 0;
valf.next = nullptr;
find(node_wrap<int_node>(list_head), node_wrap<int_node>(list_foot), valf);
return (0);
}
My compiler says
"1>main.cpp(28): error C2676: binary '!=' : 'int_node' does not define this operator or a conversion to a type acceptable to the predefined operator"
which is true.
We could define !=
in terms of ==
eg for your missing int_node
bool operator == (const int_node &i) const {return val == i.val;}
bool operator != (const int_node &i) const {return !(*this==i);}
You need to define the operators - should they check the node as well?
BTW, do you intend to return first
no matter what?
while (first != last && *first != value)
{
++first;
return first;
// ^^^^^
// |||||
}
I see two things in there:
struct int_node
does not define any comparison operator between itself and a const int_node &
instance, and that responds to your question; Iterator find(Iterator first, Iterator last, const T& value)
there is a return
statement within the while
statement, so the while
is useless, or the return
should be put outside it.
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