[RESOLVED] Using Variables for Intelligent Accessor Functions?

[phummon]

Hello everyone,

I’m an intermediate-level C++ programmer grappling with a fairly rudimentary problem. I’m creating a C++ object called FruitCart; FruitCart contains a number of integers categorizing the numbers of individual fruit in the cart. I also need FruitCart to contain accessor functions so other functions can set, retrieve, and print the fruit values. Here’s what I have so far:

--------------------------------------------------------------------------------------------------------
class FruitCart {
public:
// Constructors
FruitCart();
~FruitCart();

// Accessors
void SetApples(int a) {Apples=a;}
int GetApples() {return Apples;}
void PrintApples() {cout<<Apples;}

// Need accessor functions like the above for all kinds of fruit

protected:
int Apples; // Number of Apples in the cart
int Oranges; // Number of Oranges in the cart
int Bananas; // Number of Bananas in the cart
int Plums; // Number of Plums in the cart

// May have nearly 50 kinds of fruit!

};
--------------------------------------------------------------------------------------------------------

The problem I have is that I may have over fifty kinds of fruit in the cart! It would be a big pain to manually write out accessor functions for each kind of fruit.

I’m searching for a more intelligent solution. What I’d like to have is a general accessor function where I pass in the name of the fruit as a string (specifically, as a char * pointer) and leave everything else the same. Put in quasi-psuedocode:

--------------------------------------------------------------------------------------------------------
class FruitCart {
public:
// Constructors
FruitCart();
~FruitCart();

// Accessors
void SetFruit(int a, char * FruitType)
int GetFruit(char * FruitType)
void PrintFruit(char * FruitType)

protected:
int Apples; // Number of Apples in the cart
int Oranges; // Number of Oranges in the cart
int Bananas; // Number of Bananas in the cart
int Plums; // Number of Plums in the cart

};

void FruitCart::SetFruit(int a, char * FruitType)
{ ${FruitType} = a; }
int FruitCart::GetFruit(char * FruitType)
{ return ${FruitType}; }
void FruitCart::PrintFruit(char * FruitType)
{ cout << ${FruitType}; }
--------------------------------------------------------------------------------------------------------

Hopefully this makes sense. I know this would be simple to do in UNIX, so I’m hoping there’s a (relatively) simple way to do this in C++.

Many thanks!
-Pete

[monarch_dodra]

Hello everyone,

I’m an intermediate-level C++ programmer grappling with a fairly rudimentary problem. I’m creating a C++ object called FruitCart; FruitCart contains a number of integers categorizing the numbers of individual fruit in the cart. I also need FruitCart to contain accessor functions so other functions can set, retrieve, and print the fruit values. Here’s what I have so far:

--------------------------------------------------------------------------------------------------------
class FruitCart {
public:
// Constructors
FruitCart();
~FruitCart();

// Accessors
void SetApples(int a) {Apples=a;}
int GetApples() {return Apples;}
void PrintApples() {cout<<Apples;}

// Need accessor functions like the above for all kinds of fruit

protected:
int Apples; // Number of Apples in the cart
int Oranges; // Number of Oranges in the cart
int Bananas; // Number of Bananas in the cart
int Plums; // Number of Plums in the cart

// May have nearly 50 kinds of fruit!

};
--------------------------------------------------------------------------------------------------------

The problem I have is that I may have over fifty kinds of fruit in the cart! It would be a big pain to manually write out accessor functions for each kind of fruit.

I’m searching for a more intelligent solution. What I’d like to have is a general accessor function where I pass in the name of the fruit as a string (specifically, as a char * pointer) and leave everything else the same. Put in quasi-psuedocode:

--------------------------------------------------------------------------------------------------------
class FruitCart {
public:
// Constructors
FruitCart();
~FruitCart();

// Accessors
void SetFruit(int a, char * FruitType)
int GetFruit(char * FruitType)
void PrintFruit(char * FruitType)

protected:
int Apples; // Number of Apples in the cart
int Oranges; // Number of Oranges in the cart
int Bananas; // Number of Bananas in the cart
int Plums; // Number of Plums in the cart

};

void FruitCart::SetFruit(int a, char * FruitType)
{ ${FruitType} = a; }
int FruitCart::GetFruit(char * FruitType)
{ return ${FruitType}; }
void FruitCart::PrintFruit(char * FruitType)
{ cout << ${FruitType}; }
--------------------------------------------------------------------------------------------------------

Hopefully this makes sense. I know this would be simple to do in UNIX, so I’m hoping there’s a (relatively) simple way to do this in C++.

Many thanks!
-Pete

C++ does not do so well with converting strings to variable names. However, it works quite well with enums:

enum fruit
{
    apples,
    banana,
    pizza, //I love that fruit
    FRUIT_LAST_VALUE
};

In this case, apples will implicitly be equal to 0, banana to 1, pizza to 2, and finally, FRUIT_LAST_VALUE will have the convenience of being equal to 3, which is the size of your enum.

then in code, you can do this:

class FruitCart {
  public:
    // Constructors
    FruitCart();
    ~FruitCart();

    // Accessors
    void SetFruit(fruit iFruit, int i)  {_Fruits[iFruit] = i;}
    int GetFruit(fruit iFruit)         {return _Fruits[iFruit];}
    void PrintFruit(fruit iFruit)     {std::cout << _Fruits[iFruit];}

  protected:
    fruit _Fruits[FRUIT_LAST_VALUE]; //Array holding as many values as there are fruits. The cool part is that this should grow all by itself.

};

There, I hope that helps.

PS: A map will be able to do the string to fruit conversion you need, but I would highly advise against this type of implementation. C++ was not built for this kind of thing, and it will turn into a development nightmare. Perl was built for this, but don't force a language's paradigm into another one. When in Rome (C++) do as the Romans (C++ method of coding).

[D_Drmmr]

PS: A map will be able to do the string to fruit conversion you need, but I would highly advise against this type of implementation. C++ was not built for this kind of thing, and it will turn into a development nightmare. Perl was built for this, but don't force a language's paradigm into another one. When in Rome (C++) do as the Romans (C++ method of coding).

The difference is that with an enum your types of fruit are hard coded, whereas with a map they can be dynamic - e.g., they could be read from file. You (the OP) should pick the appropriate method according to your requirements.

[phummon]

Wow! Great advice! This is exactly what I was hoping to learn, many many thanks!!!

Yours,
-Pete