C (programming language): Difference between revisions

Created page with "C is the low-level programming language taught in UMD's CMSC216 class. ==Usage== ==Memory Allocation== There are 3 ways to allocate memory in C * <code>malloc(bytes)</code> A..."
 
No edit summary
Tag: Manual revert
 
(12 intermediate revisions by the same user not shown)
Line 1: Line 1:
C is the low-level programming language taught in UMD's CMSC216 class.
C is a low-level programming language primarilly used for kernel and embedded development.


==Usage==
==Usage==
==Memory Allocation==
===Memory Allocation===
There are 3 ways to allocate memory in C
<code>#include <stdlib.h></code><br>
There are 2 primary ways to allocate memory in C:
* <code>malloc(bytes)</code> Allocated memory is uninitialized.
* <code>malloc(bytes)</code> Allocated memory is uninitialized.
* <code>calloc(number, bytes)</code> Allocated memory is initialized to 0. Allocates (number * bytes) bytes of memory.
* <code>calloc(number, bytes)</code> Allocated memory is initialized to 0. Allocates (number * bytes) bytes of memory.
* <code>alloca(bytes)</code> [https://stackoverflow.com/questions/1018853/why-is-the-use-of-alloca-not-considered-good-practice Discouraged]
Memory allocated by <code>malloc</code> and <code>calloc</code> are on the heap and should be deallocated by <code>free</code> when no longer used to avoid memory leaks.
Memory allocated by <code>malloc</code> and <code>calloc</code> are on the heap and should be deallocated by <code>free</code> when no longer used to avoid memory leaks.<br>
 
Memory allocated by <code>alloca</code> is allocated on the stack and will automatically be freed. Do not call <code>free</code> on this memory. Do not allocate more than a few bytes using <code>alloca</code> or you will risk a stack overflow leading to undefined behavior.<br>
{{ hidden | <code>alloca</code> |
For automatically garbage collection, use [[C++]] which has smart pointers.
There is also a way to dynamically allocate memory on the stack.
* <code>alloca(bytes)</code> Usage is [https://stackoverflow.com/questions/1018853/why-is-the-use-of-alloca-not-considered-good-practice Discouraged]
Memory allocated by <code>alloca</code> is allocated on the stack and will automatically be freed at the end of the function, not scope.<br>
Do not call <code>free</code> on this memory. Do not allocate more than a few bytes using <code>alloca</code> or you will risk a stack overflow leading to undefined behavior.<br>
For automatic garbage collection, use [[C++]] smart pointers or Rust instead.
 
On Windows you also have:
* <code>_malloca</code>
* <code>_calloca</code>
These are not portable so I wouldn't use them. They are a safer version of <code>alloca</code> which allocates to the heap if there isn't enough stack space. However, you need to free them using <code>_freea</code> which eliminates the main benefit of <code>alloca</code>.<br>
As far as I can tell, the only benefit is to prevent heap fragmentation.
}}
 
[[Category:Programming languages]]