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 | C is a low-level programming language primarilly used for kernel and embedded development. | ||
==Usage== | ==Usage== | ||
==Memory Allocation== | ===Memory Allocation=== | ||
There are | <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. | ||
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.< | |||
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 | 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]] |