C (programming language): Difference between revisions

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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==

==Memory Allocation==

===Memory Allocation===

There are 3 ways to allocate memory in C

<code>#include <stdlib.h></code>

There are 2 primary ways to allocate memory in C:

* <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>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.

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.

{{ 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.

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.

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>.

As far as I can tell, the only benefit is to prevent heap fragmentation.

}}

[[Category:Programming languages]]

@@ 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==
-==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>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]]