array of struct

[miskeen]

Hello guys,

I've a class with a cpp and .h files. It's a part of a large program. I would like to create an array of structs and use it wherever in the same class, i.e. I want to initialize it in a specific function and use it in other functions within the same class.

Example:

//aFile.h
// mySimpleClass
private:
  typedef struct myStruct {
      int age;
  } MyStruct;
  void myFct1 (void) {...};
  int myFct2 (void) {...};

//aFile.cpp
// intialize an array of MyStruct in myFct1 
// use the array in the other functions

How can I do that?

Thank you!

[hag++]

You just want to dynamically allocate a new array of your struct right? Like this:

myStruct* mySimpleClass::myFunc1 (int arraySize) {
   myStruct struct1 = new myStruct[arraySize];
   return struct1;
}

[miskeen]

You just want to dynamically allocate a new array of your struct right? Like this:

myStruct* mySimpleClass::myFunc1 (int arraySize) {
   myStruct struct1 = new myStruct[arraySize];
   return struct1;
}

Yeah that's right. But there's no return in my case. So what about the following code?

void mySimpleClass::myFunc1 (void) {
  int arraySize;
  myStruct* struct1;
  // do something
  struct1 = new myStruct[arraySize];
   // do something
}

int mySimpleClass::myFunc2 (void) {
   // use the array? struct1
}

Is it correct? Because this is what I have in my case.

Thank you!

[hag++]

If you wanted to use your array of struct outside of that method's scope (myFunc1) you need to return to something, then pass it to another method (like myFunc2)

[miskeen]

So according to you, there's no global/external variable like C#? I need something that can be used by all functions of the same class and only one of those functions is able to create/initialize the array of struct.

[Sky Diploma]

Well, looking at the code you produced. the pointer struct1 is a local variable to myFunc1( ). So by the time the function call ends. the scope of struct1 ends. creating 2 problems

1) the dynamic array created remains unused.
2) The dynamic array is not deallocated with the delete operator.. Thus creating a memory leak.

There are solutions to this problem.

1. As you have mentioned. arrange a global variable .on which manipulations can be done by the functions.

2. Make your function return a pointer .. that pointer will make the allocated array usable.

[Freaky_Chris]

You can define a class wide variable within your class.

class myClass {
     private:
          myStruct mS*;

}

Which will allow you to access mS in both functions, so you could allocate the memory to it in one function. Use it in a second function and then deallocate it in another function, such as the destructor

Chris

[miskeen]

You can define a class wide variable within your class.

class myClass {
     private:
          myStruct mS*;

}

Thank you all. Thank you Chris. That's what I'm looking for.

Can I allocate memory for my array simply like this:

void mySimpleClass::myFunc1 (void) {
      int arraySize;
      // do something
      mS = new myStruct[arraySize];
      // do something
      mS[0]->age = 10;
      ...
}

Cheers!

[Freaky_Chris]

as long as arraysieze contains a value when you try to allocate memory for your array yes. Here is an exmaple,

#include <iostream>

class myLameArray {
    private:
        int *x;
        int sizee;

    public:
        ~myLameArray(){
            delete[] x;
        }

        void setUpArray(int size){
            x = new int[size];
            sizee = size;
        }

        void initArray(){
            for(int i = 0; i < sizee; i++){
                x[i] = i;
            }
        }

        void printArray(){
            for(int i = 0; i < sizee; i++){
                std::cout << x[i];
            }
        }
};

#include "myLameArray.cpp"

using namespace std;

int main(void){
    myLameArray* l = new myLameArray();
    l->setUpArray(10);
    l->initArray();
    l->printArray();

    delete l;

    return 0;
}

Chris

[miskeen]

Thank you!

[Freaky_Chris]

Your Welcome

[miskeen]

Guys, I have another question. I'm having a warning related to the fact that my variable array of structs (myStruct) is not in initialized. How can I initialize it? Is the following code the best solution?

void mySimpleClass::myFunc1 (void) {
      int arraySize;
      mS = new myStruct[1];
      // do something
      if (aCondition) {
         mS = new myStruct[arraySize];
         // do something
         mS[0]->age = 10;
      }
      ...
}