get and set char *

[Bdanielz]

Disclaimer. This is for an homework assignment (due in two weeks) and this is just one tiny aspect of the entire project that has been a major headache for me., I just would like some insight on the implementation of setting and getting a dynamic char array in the below structure.


I realize I need a setter and a getter method.
Also the string being passed in. A c-string will be random in length, so assuming this would need an dynamic char array.

Any advise or resources will be helpful. Thanks in advance.

class item
{
    public:
        item();
        ~item();
        item(const item& other);
        item& operator=(const item& other);
         //setter for Name ?
         // getter for Name ?
      private:
        char* name;
        double weight; 
    
};

[Bdanielz]

I am thinking strcpy is the way to go. as it will read from a pointer address until it hits a null char

[Bdanielz]

ok I think i have get name worked out...

class item
{
    public:
        item();
        virtual ~item();
        item(const item& other);
        item& operator=(const item& other);
        const char* GetName() const;		// returns name 
      private:
        char* name;
        double weight; 
    
};

and in .cpp

const char* item::GetName() const
// Return the name part of an entry.
{
    return name;
}

[shadowCODE]

Why are you using C strings when you'lll need dynamic memory allocation.
std::strings provides a better implementation. Or does your project specifications tie you down to C strings?

[Bdanielz]

right we are implementing the c-strings instead of using c++ built in classes.

[shadowCODE]

Ok. So you need void setName(char*);

[Bdanielz]

I think I got it.

class item
{
    public:
        item();
        virtual ~item();
        item(const item& other);
        item& operator=(const item& other);
        void getName(char * name) const;
        void setName(char * name);
    private:
        char* name;
        double weight; 
    
};

and in the .cpp

void item::getName(char * name) const
{
    //returns name
    strcpy(name, this->name);
}

void item::setName(char * name)
{
    //release the exisisting memory if there is any
    if(this->name)
        delete [] this->name;
    
    //set new name
    this->name = new char[strlen(name)+1];
    strcpy(this->name, name);
}

[NoXzema]

if(this->name)
        delete [] this->name;

You can safely reduce this to: delete[] this->name;

What if name isn't null terminated? I would change the function signature to:
void item::setName(const char* name, size_t size)
then take advantage of the size parameter, which should be the size of the string passed. We pass const for name so we assure the user of said function that we do not modify the buffer passed. Instead of using strlen and strcpy, you would instead use size and strncpy.

[Bdanielz]

We have a "driver" file that is not passing the size of the string.
So I am not "allowed" to pass the length of the string in the client.

[Bdanielz]

@NoXzema

if(this->name)
        delete [] this->name;

You can safely reduce this to:

delete[] this->name;

Isn't the the if ( ) test important, what if the program tries to free memory that is not allocated?

[shadowCODE]

Isn't the the if ( ) test important, what if the program tries to free memory that is not allocated?

You RIGHT!

[NoXzema]

Sorry, I thought I had included a short explanation. The check simply checks the pointer for being valid. A valid pointer is anything that isn't a null pointer. delete already makes a check for null pointers whenever you pass a pointer to it. If the pointer passed is a null pointer, it's a no-op. By having the if statement there, you're simply checking for null pointers twice. Instead, you should simply make sure the pointer is a null pointer when it's not valid and pass the pointer to delete directly.

[Bdanielz]

Gotcha. Thanks for the input.