determine length of calloc array of TCHARs (not string length) [duplicate]

This question already has answers here: Determine size of dynamically allocated memory in C (15 answers) Close开发者_StackOverflow社区d 9 years ago.

I have this code:

TCHAR *sRes;
sRes = (TCHAR *) calloc(16384, sizeof(TCHAR));
DWORD dwRes = sizeof(sRes);

dwRes is always 8, and of course _tcslen(sRes) is always 0.

I am looking for 16384.

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In C there is no way to get the size of a memory block with only the base address of the block.

But when you created the block, you knew the size: just save it and use it afterwards when you need:

TCHAR *sRes;
DWORD dwRes = 16384 * sizeof (TCHAR);
sRes = calloc(16384, sizeof (TCHAR)); /* I prefer `sizeof *sRes` */

/* use `sRes` and `dwRes` as needed ... */

Also, notice I removed the cast from the return value of calloc. Casting here serves no useful purpose and may hide an error.

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There is no supported mechanism for obtaining size of a block allocated with malloc or calloc. If you call HeapAlloc instead you may call HeapSize thereafter.

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The operating system and the underlying memory allocator implementation keep track of that number, but there is no standard facility to obtain this value in application code.

sizeof is a static operator and hence cannot be used to return the size of anything that's determined at runtime.

Your only option is to create a custom struct where you manually keep both the returned pointer and the size which was allocated.