I have a class called AString
. It is pretty basic:
class AString
{
public:
AString(const char *pSetString = NULL);
~AString();
bool operator==(const AString &pSetString);
...
protected:
char *pData;
int iDataSize;
}
Now I want to write code like this:
AString *myString = new AString("foo");
if (myString == "bar") {
/* and so on... */
}
However, the existing comparison operator only supports
if (*myString == "bar")
If I omit that asterisk, the compiler is unhappy.
Is there a way to allow the comparison operator to compare *AString
with const char*
?
[ Original answer was wrong and thus corrected below ]
As pointed out by Oli Charlesworth, in a comment below, this is impossible.
You would need to define an operator like
but you cannot overload an operator unless one of its parameters is non-primitive type - and pointers (both pointers to AString and pointers to char) are primitive types.
Not unless you wrap it in some sort of smart-pointer class, but that would make the semantics weird. What's wrong with
if (*myString == "bar")
?even if you get it to work, is very confusing for others. You are comparing a pointer to an object with a string literal. A much clearer way to get this working is dereference the pointer, and provide an overload like
I think what you want is wrong since it obscures the type system of C++.
myString
is a pointer to aAString
and not aAString
. Dont't try to hide the fact that it's a pointer. It's an entry point for ugly bugs and if you're coding in a team everyone else would be nothing but confused!No, there is not.
To overload
operator==
, you must provide a user-defined type as one of the operands and a pointer (eitherAString*
orconst char*
) does not qualify.And when comparing two pointers, the compiler has a very adequate built-in
operator==
, so it will not consider converting one of the arguments to a class type.