Differences

This shows you the differences between two versions of the page.

--- header-guard [May 14, 2026 at 12:52] – yanevskiv
+++ header-guard [May 14, 2026 at 13:01] (current) – yanevskiv
@@ Line 1: / Line 1: @@
 # Header guard
-**Header guards** are a pattern used in C and C++ programming languages when writing header files.
+**Header guards** are a pattern used in C and C++ programming languages when writing header files. Header files (.h files) are files that are included in source files (.c and .cpp files) near the top (hence the name) using the `#include <...>` directive. They are used to allow multiple inclusions of the same file but prevent multiple definition errors.
-Header files are files that
-A prototypical example of a header guard is the following
+Header guards follow the same general pattern:
 ```c
-// my_header.h
+#ifndef __HEADER_GUARD_H__
-#ifndef __MY_HEADER_H__
+#define __HEADER_GUARD_H__
-#define __MY_HEADER_H__
+// ...
+#endif /* __HEADER_GUARD_H__ (This is just a comment) */
+```
+In C and C++ programming languages, `#include` is nothing but text substitution. If you include something multiple times
+## Example
+A prototypical example of a header guard is the following.
+```c
+// hello_world.h
+#ifndef __HELLO_WORLD_H__
+#define __HELLO_WORLD_H__
 struct Hello {
-    const char *world;
+    const char *text = "world";
 };
-#endif /* __MY_HEADER_H__ */
+#endif /* __HELLO_WORLD_H__ */
 ```
+This allows multiple inclusion of "hello\_world.h"
+```c
+// main.c
+#include <hello_world.h>
+#include <hello_world.h>
+int main() {
+    Hello world;
+    return 0;
+}
+```