Using new and delete

[ETAkoG1T]

why doesn't this work? (Error: corrupt data)

code:

Cow & Cow::operator=(const Cow & c)
{
	int len = 1 + strlen(c.name);
	int i = 0;
	for(;i<19 && c.name[i];i++)
		name[i] = c.name[i];
	name[i] = '\0';
	delete[] hobby;
	hobby = new char[strlen(c.hobby) + 1];
	strcpy(hobby, c.hobby);
	weight = c.weight;
	return *this;
}

[Dy7SLyTq]

remove && c.name[i] on line 6 and you need to declare hobby and weight

[ETAkoG1T]

The code is part of a program... This is the class members,
// char name[20];
// char * hobby;
// double weight;
I use new in my constructor, I don't see why this doesn't work!

[TheIdeasMan]

Is there any reason why name & hobby are an array of char and not a std::string?

That would make things a lot easier wouldn't it?

Why do you have a copy assignment operator anyway? It does not seem to do anything different to the implicit default one.

[ETAkoG1T]

The default would just copy the address instead of copying the contents... And it is a programming exercise, can't use string, that would be cheating.

[cire]

The only obvious problem I see with your operator= is that it will fail miserably for self assignment. Another caveat is that it isn't exception safe.

I would expect something more like:

Cow& Cow::operator=(const Cow& c)
{
    using std::strlen ;

    if ( &c != this )
    {
        if ( strlen(hobby) < strlen(c.hobby) )      // attempt memory allocation before making any changes.
        {
            char * mem ;
            mem = new char[strlen(c.hobby)+1] ;
            delete [] hobby ;
            hobby = mem ;            
        }

        std::copy(c.name, c.name+strlen(c.name)+1, name) ;
        std::copy(c.hobby, c.hobby+strlen(c.hobby)+1, hobby) ;
    }

    return *this ;
}

But I suspect your problem lies elsewhere.

[ETAkoG1T]

Yep, didn't really solve the problem but thx, this is the class decleration:

class Cow {
private:
	char name[20];
	char * hobby;
	double weight;
public:
	Cow();
	Cow(const char * nm, const char * ho, double wt);
	Cow(const Cow & c);
	~Cow();
	Cow & operator=(const Cow & c);
	void ShowCow() const;
};

[Disch]

I don't see a problem with this ctor. The problem must be elsewhere.

[ETAkoG1T]

anything wrong with this code?:

int main()
{
	Cow var;
	Cow var2("cow", "running", 393.8);
	var.ShowCow();
	var2.ShowCow();
	var = var2;
	var.ShowCow();

	std::cin.get();
	return 0;
}

[ETAkoG1T]

it may be that the constructors that are wrong...

Cow::Cow(const char * nm, const char * ho, double wt)
{
	int i = 0;
	for(; i < 19; i++)
	{
		name[i] = nm[i];
	}
	name[i] = '\0';
	hobby = new char[strlen(ho) + 1];
	strcpy(hobby, ho);
	weight = wt;
}

Cow::Cow(const Cow & c)
{
	strcpy(name, c.name);
	name[strlen(name + 1)] = '\0';
	hobby = new char[strlen(c.hobby) + 1];
	strcpy(hobby, c.hobby);
	weight = c.weight;
}

[cire]

name[strlen(name + 1)] = '\0';

That is certainly wrong.. and completely unnecessary, although I doubt it's the cause of your problems. The chief suspect at this point is your default constructor.

[ETAkoG1T]

I can confirm that it didn't solve the problem. But yea, it also looks wrong to me when I think about it.

[ETAkoG1T]

It only works when I don't use the default constructor...

Cow::Cow()
{
	name[0] = '\0';
	hobby = NULL;
	weight = 0.0;
}

[ne555]

You dereference `hobby' being NULL.

[cire]

In order to avoid code to handle the special case where hobby is null, you may want to go ahead and allocate some memory in the default constructor.

Cow::Cow() : hobby(new char[1]), weight(0.0)
{
     name[0] = hobby[0] = '\0' ;
}