Alias to return an array

Not making sense to me. Ok, I have defined an alias to in as:

Code:

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typedef int arrT[10];

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I understand arrT to be an alias for an int[10]; Arrays convert to pointers to the first element. Thus, if I define a function as such:

Code:

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arrT *func(int i);
arrT *func(int i){

      static int arr[i];
      int *parr = arr;
      return  parr;
}

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This is wrong as I can't return a pointer to int because it is expecting an int (*)[] to be returned. What am I not getting here?

Well, you are telling the compiler that you are returning a pointer to an array of 10 elements, so:

Code:

---

typedef int arrT[10];

arrT* func(int i);
arrT* func(int i)
{
        static int arr[10];
        return &arr;
}

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Btw, you cannot initialize the array with a variable "i". This is not allowed in ISO C++.
If you need to do so, you should use a vector:

Code:

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typedef vector<int> arrT;

arrT& func(int i);
arrT& func(int i)
{
        static std::vector<int> arr(i);
        return arr;
}

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But why are you trying to return an array in this manner?

I do not see the point in making the internal vector static unless you want all the pointers returned to point to the same vector.

In fact, why not just --

Code:

---

vector<int> func(int i) {
  vector<int> arr(i);
  return arr;
}

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If you are going to completely change everything? Vectors are copyable after all.

Thank you for the quick responses. The intent is not to play with arrays in C++ instead of vectors but if I need to play with arrays in C++ and perhaps return one from a function, I know ways in which I can do that.

My confusion was with int* and int (*)[]; the conversion being impossible and I just did not know how to resolve this.

Quote:

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Originally Posted by whiteflags

In fact, why not just --

Code:

---

vector<int> func(int i) {
  vector<int> arr(i);
  return arr;
}

---

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Should the vector not be static since you are returning a vector that is local to the block and when func returns, the memory is reused?

Quote:

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Originally Posted by Elysia

Well, you are telling the compiler that you are returning a pointer to an array of 10 elements, so:

Code:

---

typedef int arrT[10];

arrT* func(int i);
arrT* func(int i)
{
        static int arr[10];
        return &arr;
}

---

Btw, you cannot initialize the array with a variable "i". This is not allowed in ISO C++.
If you need to do so, you should use a vector:

Code:

---

typedef vector<int> arrT;

arrT& func(int i);
arrT& func(int i)
{
        static std::vector<int> arr(i);
        return arr;
}

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But why are you trying to return an array in this manner?

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Thank you, I agree a vector is a better solution and I understand that vector should be used over array but for my own knowledge, I am choose to return a pointer to an array.

Quote:

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Originally Posted by Imanuel

Thank you for the quick responses. The intent is not to play with arrays in C++ instead of vectors but if I need to play with arrays in C++ and perhaps return one from a function, I know ways in which I can do that.

My confusion was with int* and int (*)[]; the conversion being impossible and I just did not know how to resolve this.

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You can also use a C++ array to do it:

Code:

---

std::array<int, 10> func(int i)
{
        std::array<int, 10> arr({ /* initialize it here */});
        return arr;
}

---

This sample requires C++11 for initializer lists and TR1 or C++11 for std::array. See my sig for information on how to enable C++11 for your compiler.

Quote:

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Originally Posted by Imanuel

Should the vector not be static since you are returning a vector that is local to the block and when func returns, the memory is reused?

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No. Since a vector is an object, a copy of the object is made upon returning, so it is fine.
(We don't need to worry about how a vector works internally.)

yes, saw std::array<int, 10> in another post. Ok you guys rock and thank you so much for clearing this up.