Re: operator+() code for objects
silentway wrote:
I am trying to create a simple vector class with overloaded operators
for assignment, +=, -=, +, *, etc
My code for the overloaded operators worked OK, until I tried
operator+(). The problem is that I can not return a local variable.
Huh?
This is fair enough, but I am sure that this used to work ok
10 years ago, when I was using Zortech compiler. I am back to
C++ after an outrageously long break without doing any codng.
Get a good book. Many things changed.
#include <iostream>
class vec
{
public:
vec(float x = 0.0) : mx(x) { printf("in constructor\n"); };
vec(vec &rv) : mx(rv.mx) { printf("in copy constr\n"); };
virtual ~vec() {};
void setx(float x) {mx = x;};
vec & operator=(const vec &rv);
vec & operator+=(const vec &rv);
const vec operator+(const vec &A) /*const*/;
void print(char *msg);
private:
float mx;
};
Several things here:
1. Make one-argument constructor 'explicit' to avoid accidental
construction.
2. Do not create a virtual destructor for objects you don't plan to use
polymorphically.
3. You #include <iostream> but use printf() for which you didn't include any
header.
4. What is print()? Why does it take a pointer to a non-const char? What
does it to the memory pointed to by it?
5. Do not blindly terminate lines with a semicolon. You don't need them
after the definition of a function. I consider it a quirk, but it is
actually allowed in the standard when defining a function as part of the
class definition, but not outside.
6. Your copy-constructor takes a reference to a non-const object. This is
most surely wrong and this oversight is also causing you problems.
const vec vec::operator+(const vec &A) /*const*/ {
printf("in vec vec::operator+(const vec &A)\n");
vec result(*this);
result += A;
return result;
}
The copy-constructor that doesn't take a reference to const is what breaks
this. When fixed, you could also make the operator const. However, there is
another thing you should know, and that is that operators don't have to be
defined as memberfunctions:
vec operator+(vec const& v1, vec const& v2) {
vec res(v1);
res += v2;
return res;
}
This is the typical implementation for operator+ based on operator+=, which
needs to remain inside the class. Note that you can also overload a free
operator for the combination vec/float or float/vec, which wouldn't work for
a bound one.
g++ -g vec.cpp -o vec -lm
Add -Wall
Uli
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