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Overloading member access operators ->, .*
(5 answers)
Closed 3 years ago.
I have implemented a Matrix class implementation for matrix manipulation, and so far i can overload ordinary (single) operators such as +, *, ...
I want to do Matrix elementary multiplication by overloading the operator (.*), such as i can write
Matrix A(5,3), B(5, 3), C;
C = A .* B;
C, in this case, will hold the value of multiplication element by element from A and B (A and B have same dimensions)
From this operator overloading reference
Restrictions
The operators :: (scope resolution), . (member access), .* (member access through pointer to member), and ?: (ternary conditional) cannot be overloaded.
In short, it's not possible to overload the "dot" member access operators like .*.
Here you can see the "pointer to member of object" .* operator is not overloadable in c++.
Related
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What is the "-->" operator in C++?
(29 answers)
Closed 4 years ago.
I have encountered <<++ and >>++ operators many time in`C++, but I don't understand what they are. What is the specific meaning and use of these operators, and how are they different from right shift and left shift operator?
C++ compilers ignore whitespace unless in certain situations such as string literals.
<<++ and >>++ is really just a bit-shift operatior << or >>, followed by an increment operator ++.
Consider this code:
a <<++ b is equivalent to
a<<++b because the spaces are ignored in this context, and then equivalent to
a << ++b (a left shifted by a pre-incremented b)
a << (++b) due to operator precedence. Bit shift operators have lower precedence than incrementation.
There are two separate operators in both cases: left shift (<<), right shift (>>) and increment operator (++).
You can rewrite the following:
a >>++ b
as:
a >> (++b)
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Operator overloading
I was wonder how can I over load the Conditional operator in cpp?
int a,b,c;
a=10;
b=11;
c = (a>b) ? a : b;
Is it possible?
You cannot overload the conditional operator.
Several operators cannot be overloaded. These operators take a name, rather than an object, as their right operand:
Direct member access (.)
Deference pointer to class member (.*)
Scope resolution (::)
Size of (sizeof)
The conditional operator (?:) also cannot be overloaded.
Additionally, the new typecast operators: static_cast<>, dynamic_cast<>, reinterpret_cast<>, and const_cast<>, and the # and ## preprocessor tokens cannot be overloaded.
http://www.informit.com/guides/content.aspx?g=cplusplus&seqNum=23
No, you can't overload the conditional operator, since it's simply shorthand for a simple if..else block.
You can however overload the operators used in the condition, but not for primitive types such as int, like you have in your example above.
is subscript operator [ ] unary or binary operator ?
I'm quite new to C++ and was going through operator operloading and wondered
is subscript a unary or binary?
The subscript operator is a binary operator in the strict sense as it takes two arguments, the reference to the object and the value.
int arr[3];
Here you can see that [] operator makes use of both arr and 3.
According to the C++ Standard
13.5.1 Unary operators
1 A prefix unary operator shall be implemented by a non-static member
function (9.3) with no parameters...
and
13.5.2 Binary operators
1 A binary operator shall be implemented either by a non-static member
function (9.3) with one parameter...
Thus the subscript operator is a binary operator.
The Unary operators in C++ are:
unary-operator: one of
* & + - ! ~
and also you may add to unary operators
++ cast-expression
-- cast-expression
In c++ I implemented an integer class and I overloaded operator ^ to be the power function.
integer integer::operator^ (const integer& rhs){
return integer(pow(this->.i, rhs.i));
}
This is working correctly for two operands.
integer i1, i2, i3 ;
i4 = i1 ^ i2 ^ i3;
The value of i4 is wrong mathematically because associativity required right-to-left. How can I solve this problem? How do I change associativity?
I got reasonable answers and I learn:
-We can't change associativity or priority of an operator.
-Good is Not to overload operators to do something conceptually different to
the built-in versions
-Even compiler can't support; it hard to implement!
You cannot change the associativity or priority of an operator in C++ by overloading it. These rules are hardwired into the language syntax.
The C++ standard says (§13.5.6, emphasis mine):
An operator function shall either be a non-static member function or be a non-member function and have
at least one parameter whose type is a class, a reference to a class, an enumeration, or a reference to an
enumeration. It is not possible to change the precedence, grouping, or number of operands of operators.
The meaning of the operators =, (unary) &, and , (comma), predefined for each type, can be changed [...]
Not only is the ^ operator left-associative, but it also has a very low precedence. The correct precedence for a power operator should be higher than the multiplication (so priority 4 or better on this table), but it has priority 10--this means that even additions and subtractions are evaluated before it. 1 + 2 ^ 3 * 4 will be parsed as (1 + 2) ^ (3 * 4), while a mathematically correct power operator should parse as 1 + (2 ^ 3) * 4.
If the associativity or priority of an operator could be modified, a huge, huge syntactical mess would ensue. My humble opinion is that you should not try to overload the ^ operator to use it as a power operator. I would rather make a power method on the class.
In C++, I can change the operator on a specific class by doing something like this:
MyClass::operator==/*Or some other operator such as =, >, etc.*/(Const MyClass rhs) {
/* Do Stuff*/;
}
But with there being no classes (built in by default) in C. So, how could I do operator overloading for just general functions?
For example, if I remember correctly, importing stdlib.h gives you the -> operator, which is just syntactic sugar for (*strcut_name).struct_element.
So how can I do this in C?
Thank you.
Plain old C does not have operator overloading in any form. The -> "operator" to access a member of a pointer is standard C and is not introduced by any header file.
Built-in operators in C language are overloaded. The fact that you can use binary + to sum integers, floating-point numbers and perform pointer arithmetic is a canonical example of operator overloading.
However, C offers no features for user-level operator overloading. You can't define your own operators in C.
The -> structure pointer dereferencing operator is part of the C spec. stdlib.h does not affect this.
Sure, you can't overload operators in C.
The -> operator is part of the C language, no #include needed.