Question

I am programming in C. I am using also a library to create tasks which can communicate among them via messages. The content of these messages must be the pointer to the data you want to exchange.

In my case I want to send an array so I am sending a pointer to the array. In the receiving task I can then access the different elements by increasing the pointer, but, is there a way to know how long the array was?

Thank you in advance.

Answer 1

No, there is no way to do this as arrays decay to pointers when passed to functions, thus all information regarding size is lost.

• You can include another parameter to specify the array length

  void func(int len, int arr[]);
  

• You can mark the end of the array with a special value (perhaps like argv does)

• You can put your array into a structure and pass that (and suffer the performance penalties) or pass the a pointer to the structure

  struct args {
      int arr[100];
  };
  

If you decide to go the first route, you can use a nice feature of C99, even if it doesn’t actually enforce that arr has at least len elements:

void func(int len, int arr[len]);