If I want to dynamically allocate memory for array of pointers of int, how can I achieve this requirement?
Suppose I declare an array of pointers of int like this:
int (* mat)[];
Is there a way I can allocate memory for K number of pointers dynamically and assign it to mat? If I do
mat = new int * [K];
It gives error : cannot convert 'int**' to 'int (*)[]' in assignment
. I understand this memory allocation is implicitly got converted to int **. Is there any way to allocate memory for above scenario?
Even when I try to assignment of statically allocated array of pointers of int to array of pointers of int, like this:
int (*mat)[] = NULL;
int (* array_pointers)[26];
mat = array_pointers;
Compilation gives this error: cannot convert 'int (*)[26]' to 'int (*)[]' in assignment
.
Can someone please explain to me why this is an error or why it should be an error?
Answer
In C, int (* mat)[];
is a pointer to array of int
with unspecified size (not an array of pointers). In C++ it is an error, the dimension cannot be omitted in C++.
Your question says new int *[K]
so I assume this is really a C++ question. The expression new T[n]
evaluates to a T *
already, there is no implicit conversion.
The code to allocate an array of null pointers using new
is:
int **mat = new int *[10]();
Then mat
points to the first one of those. Another option (less commonly used) is:
int * (*mat)[10] = new int *[1][10]();
where *mat
designates the entire array of 10 pointers.
NB. This sort of code is not useful for anything except demonstration purposes perhaps, whatever you are trying to do has a better solution.
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