IIRC there’s one picky point. malloc is guaranteed to return an address aligned for any standard type. ::operator new(n) is only guaranteed to return an address aligned for any standard type no larger than n, and if T isn’t a character type then new T[n] is only required to return an address aligned for T. … 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
The variable e is a pointer to an array of n + 1 elements of type double. Using the dereference operator on e gives you the base-type of e which is ” array of n + 1 elements of type double“. The malloc call simply takes the base-type of e (explained above) and gets its … Read more
The sbrksystem call moves the “border” of the data segment. This means it moves a border of an area in which a program may read/write data (letting it grow or shrink, although AFAIK no malloc really gives memory segments back to the kernel with that method). Aside from that, there’s also mmap which is used … Read more
According to the specifications, malloc(0) will return either “a null pointer or a unique pointer that can be successfully passed to free()”. This basically lets you allocate nothing, but still pass the “artist” variable to a call to free() without worry. For practical purposes, it’s pretty much the same as doing: artist = NULL;
From http://computer-programming-forum.com/47-c-language/a9c4a586c7dcd3fe.htm: In pre-ANSI C — as described in K&R-1 — malloc() returned a char * and it was necessary to cast its return value in all cases where the receiving variable was not also a char *. The new void * type in Standard C makes these contortions unnecessary. To save anybody from the … Read more
You likely forgot to #include <stdlib.h>
Setting unused pointers to NULL is a defensive style, protecting against dangling pointer bugs. If a dangling pointer is accessed after it is freed, you may read or overwrite random memory. If a null pointer is accessed, you get an immediate crash on most systems, telling you right away what the error is. For local … Read more
Presumably you mean heap from a memory allocation point of view, not from a data structure point of view (the term has multiple meanings). A very simple explanation is that the heap is the portion of memory where dynamically allocated memory resides (i.e. memory allocated via malloc). Memory allocated from the heap will remain allocated … Read more
The short version: Always use calloc() instead of malloc()+memset(). In most cases, they will be the same. In some cases, calloc() will do less work because it can skip memset() entirely. In other cases, calloc() can even cheat and not allocate any memory! However, malloc()+memset() will always do the full amount of work. Understanding this … Read more