Hey guys, here's a newbie question:
suppose I have a ptr to an int, and I allocate memory to it dynamically.
after all the allocations are done, how can I get the number of ints (elements) in my array?
i feel like I can do this with some fancy sizeof stuff, instead of maintaining a counter..
Thanks for the help!!
You can't.
You have to maintain a counter.
If you want someone to keep the counter for you, use a vector.
Well there is sizeof foo / sizeof foo[0]; but that expression only works for arrays that are in scope. So don't use it after you pass foo to a function, the type is different.
Well usually you can do something like:
Output:Code:int *ptrArray = NULL; int nNumberOfInts = 20; unsigned totalSize = nNumberOfInts * sizeof(int); ptrArray = (int*) malloc(totalSize); // ptrArray now points to a block of memory that is // number of elements * the size of an int // so printf("Total size of block of %d integers should be: %d\n", nNumberOfInts, totalSize); printf( "Or, sizeof(ptrArray[0] * nNumberOfInts = %d\n", sizeof(ptrArray[0]) * nNumberOfInts);
Guess it worksCode:jeff@jeff-gate:~/dev/arraysize$ ./arraysize_test arraysize_test 1.0 Testing: arraysize Total size of block of 20 integers should be: 80 Or, sizeof(ptrArray[0] * nNumberOfInts = 80 jeff@jeff-gate:~/dev/arraysize$
Last edited by jeffcobb; 05-11-2010 at 11:51 PM.
And it won't work for dynamic arrays.
sizeof() is a compile-time operator.
I see. So I can do that with arrays (the sizeof stuff), but not pointers.
Thanks for the help guys! you are all really fast!
Last edited by dayalsoap; 05-11-2010 at 11:42 PM.
