Finding length of Dynamic Array in C/C++

[Maxood]

I have the following code:

int* y = new int[n];

where n's value will be provided by the user at runtime. I need to know the total memory size that i have allocated to y.

What function i will use? Wonder if i can use the sizeof operator? Also i i use the sizeof operator in such a situation as:

int x[10];
cout<<sizeof(x) ;

then it returns 40. What is 40 exactly?

[Banfa]

You can not work out the size of allocated data from y alone, you need n too

size = sizeof *y * n;

That is the size of a single object times the number of objects allocated, if you prefer

size = sizeof(int) * n;

int because y is int*.

The size of x, 40, is the size of the entire array x. This is also the size of a single entry in x, x[4] for example time the number of entries in x. Since x is an array of 10 integers with size 40 you can deduce from this that sizeof int for your system is 40/10 = 4.

[RRick]

You can not work out the size of allocated data from y alone, you need n too
......
size = sizeof(int) * n;

That's the problem with using C/C++ arrays. If you want to avoid overflowing or out of bounds elements in the array, you must keep track of the size (i.e. the n value). If this sort of thing seems laborious and dangerous, try the STL vector. It deals with those issues.

[sandipan169]

try using _countof()