Thread: sizeof on arrays

What should i do to make this code return the size of my dynamic allocated array. it just says that its 4 bytes, but I want all of the array

Code:

 
  floatarray = new float[7];
  for (k=0;k<7;k++) floatarray[k]=(k+1);
  cout << "size of floatarray" << sizeof(floatarray) << endl;

// cout << "size of floatarray" << strlen(floatarray) << endl;

Kuphryn

I don't think that's possible with dynamic arrays (only static).
The sizeof(floatarray) returns the size of the pointer, not the array itself.

As Monster says, you can only do this on an array (not an extern of an array, or an array generated by calling new)

Do this

Code:

int floatarraysize = 7;
floatarray = new float[floatarraysize];
cout << "size of floatarray" << floatarraysize << endl;

Your implementation may provide a NON-Standard way of doing this, but you'd have to read the manuals to find it (assuming it was even provided).

Interesting.

I have never tried using strlen(pointertoArray).

How about strlen(array[]) or strlen(array[0])?

Kuphryn

> I have never tried using strlen(pointertoArray).
Since its only valid to try this on char arrays which have a \0 terminator, it isn't really applicable.

In addition
char arr[80] = "hello";

sizeof(arr) is 80
strlen(arr) is 5

So it doesn't really help that much even when you have strings

if you use C memory allocation routines like:
malloc calloc,realloc you could use
special function called msize wich returns the size of the mem

like:

Code:

#include <malloc.h>
    ....
   float array = (float*)malloc(10 * sizeof(float));
   ...
   /// do something 
   ...
   int memsz =0;
#ifdef WIN32
   memsz = _msize(array); //Win32 specific name (ANSI name is msize)
#else
   memsz = msize(array);
#endif

  //free the mem
  free(array);

you can try this with NEW and DELETE
but i don't know the result (wether it will be succesfull or portable)

The size of an array is the size of the element multiplied with the number of places in the Array.

thx guys and gals. I had to put in a counter which i increased every time i increased the size of the dynamic array.

Therefore, sizeof(array)/sizeof(array[0]) will give you the size of each individual element. Couldn't you derefrence the array if it's dynamic to find out how large it is?