Suppose that you have the structure. struct S { short a; int b; char c, d; }; Without alignment, it would be laid out in memory like this (assuming a 32-bit architecture): 0 1 2 3 4 5 6 7 |a|a|b|b|b|b|c|d| bytes | | | words The problem is that on some CPU architectures, the … Read more
Well, if you want to allocate array of type, you assign it into a pointer of that type. Since 2D arrays are arrays of arrays (in your case, an array of 512 arrays of 256 chars), you should assign it into a pointer to array of 256 chars: char (*arr)[256]=malloc(512*256); //Now, you can, for example: … Read more
I don’t think that there are any guarantees in the language standard, but modern operating systems which support sparse virtual memory and memory protection (such as MacOS X, Linux, all recent version of Windows, and all currently manufactured phone handsets) automatically clean up after badly-behaved processes (when they terminate) and free the memory for you. … Read more
After trying some things, I finally managed to figure out how to do this. First of all, in glibc, malloc is defined as a weak symbol, which means that it can be overwritten by the application or a shared library. Hence, LD_PRELOAD is not necessarily needed. Instead, I implemented the following function in a shared … Read more
You don’t have to track it by your self! size_t malloc_usable_size (void *ptr); But it returns the real size of the allocated memory block! Not the size you passed to malloc!
OK, there’s a fair deal of confusion explaining exactly what order the necessary free() calls have to be in, so I’ll try to clarify what people are trying to get at and why. Starting with the basics, to free up memory which has been allocated using malloc(), you simply call free() with exactly the pointer … Read more
You need to add: #include <stdlib.h> This file includes the declaration for the built-in function malloc. If you don’t do that, the compiler thinks you want to define your own function named malloc and it warns you because: You don’t explicitly declare it and There already is a built-in function by that name which has … Read more
Because the size of the “string” pointer is 8 bytes. Here are some examples of using sizeof() with their appropriate “size”. The term size_of() is sometimes deceiving for people not used to using it. In your case, the size of the pointer is 8 bytes.. below is a representation on a typical 32-bit system. sizeof … Read more
The <malloc.h> header is deprecated (and quite Linux specific, on which it defines non-standard functions like mallinfo(3)). Use <stdlib.h> instead if you simply need malloc(3) and related standard functions (e.g. free, calloc, realloc ….). Notice that <stdlib.h> is defined by C89 (and later) standards, but not <malloc.h> Look into /usr/include/malloc.h you’ll find there some non-standard … Read more
This is undefined behaviour, as there’s no way to reliably prove that memory behind the pointer was allocated correctly (i.e. by new for delete or new[] for delete[]). It’s your job to ensure things like that don’t happen. It’s simple when you use right tools, namely smart pointers. Whenever you say delete, you’re doing it … Read more