I want to declare an array that is stored in a pointer A. I have the following code.
int length = 8;
int *A;
A = (int*) malloc(length*sizeof(int));
A = {5, 1, 3, 5, 5, 2, 9, 8};
However, the array cannot be initialized like above. The error says "cannot convert to 'int' in assignment". How do I fix this issue?
Additionally, are malloc and memset necessary in c++ when declaring an array (for a pointer)?
Thanks!
Quick answer:
A[0] = 5;
A[1] = 1;
A[2] = 3;
A[3] = 5;
A[4] = 5;
A[5] = 2;
A[6] = 9;
A[7] = 8;
Basically, when you say "A = " you are changing "what A is pointing to". If you want to change "the value of what A is pointing to" you must use [] or *.
cplusplus.com has a good article on that topic
Edit
I must warn you that it is not a good pratice to use malloc in C++ because it will not initialize neither destruct complex objects.
If you have:
int length=8;
class C_A {
C_A() {
std::cout << "This cout is important" << std::endl;
}
~C_A() {
std::cout << "Freeing is very important also" << std::endl;
}
};
C_A* A;
A = (C_A*) malloc(length*sizeof(C_A));
free(A);
You will notice that the cout will never happen, while the correct is:
A = new C_A[length];
delete[] A;
NO. You don't need malloc to declare an array as a pointer since an array in its nature is a pointer. The difference between using malloc or no is that when using malloc the array is declared in the heap instead of the stack.
Second, you can fill an array directly if and only if you are filling it when declaring e.g.
This is right : int a[3]={1,2,3};
This is wrong :
int a[3];
a= {1,2,3};
A reasonably efficient way to do what you want, with malloc() and memcpy(), is
int initializer[] = {5, 1, 3, 5, 5, 2, 9, 8};
int *A;
A = (int*) malloc(length*sizeof(int));
memcpy(A, initializer, length*sizeof(int));
Use new instead of malloc, it returns T* and not void*, and support exception:
int *A = new int[length];
malloc only works in specific cases. I would definitely advise staying away at least until you understand why.
std::vector.std::vector<int> A{5, 1, ..., 8};