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I am trying to deal with operator overloading at the first time, and I wrote this code to overload ++ operator to increment class variables i and x by one.. It does the job but the compiler showed these warnings:

Warning 1 warning C4620: no postfix form of 'operator ++' found for type 'tclass', using prefix form c:\users\ahmed\desktop\cppq\cppq\cppq.cpp 25

Warning 2 warning C4620: no postfix form of 'operator ++' found for type 'tclass', using prefix form c:\users\ahmed\desktop\cppq\cppq\cppq.cpp 26

This is my code:

class tclass{ public: int i,x; tclass(int dd,int d){ i=dd; x=d; } tclass operator++(){ i++; x++; return *this; } }; int main() { tclass rr(3,3); rr++; rr++; cout<<rr.x<<" "<<rr.i<<endl; system("pause"); return 0; }
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3 Answers 3

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12

This syntax:

tclass operator++()

is for prefix ++ (which is actually normally written as tclass &operator++()). To distinguish the postfix increment, you add a not-used int argument:

tclass operator++(int)

Also, note that the prefix increment better return tclass & because the result may be used after: (++rr).x.

Again, note that the postfix increment looks like this:

tclass operator++(int) { tclass temp = *this; ++*this; // calls prefix operator ++ // or alternatively ::operator++(); it ++*this weirds you out!! return temp; }
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5 Comments

++*this; wierds me out. I use ::operator++();. Which wierds others out.
++*this; shows error saying: Error 1 error C2675: unary '++' : 'tclass' does not define this operator or a conversion to a type acceptable to the predefined operator c:\users\ahmed\desktop\cppq\cppq\cppq.cpp 14
@Shahbaz: I am using MS VC++.
Microsoft Visual C++ is one of the least standard-conforming compilers. (Specially version 6 which was written before C++ became standard). Personally, I would suggest coding in a real compiler. If you are stuck with it, you'd have to refer to msdn to understand its shortcomings and its workarounds. Either way, the way I wrote it is the standard.
@Shahbaz: MSVC is definitely a real compiler. MSVC6 was replaced in 2002. That's (roughly) the equivalent of GCC 3.0.4. More likely he did something wrong. Unrelated: the return type of operator++() is usually tclass&.
6

There are two ++ operators. You defined one and used the other.

tclass& operator++(); //prototype for ++r; tclass operator++(int); //prototype for r++;
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5

There are separate overloads for postincrement and preincrement. The postincrement version's signature is operator++(int), while the preincrement's signature is operator++().

You have defined operator++(), so you've only defined preincrement. However, you use postincrement on an instance of your class, so the compiler tells you that it will use a call to the preincrement function because no postincrement is defined.

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