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[c/en] Added a section for header files.

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Added a section for header files.
Included a discussion of what belongs in a header file and what does
not.
This commit is contained in:
Zachary Ferguson 2015-10-07 23:45:01 -04:00
parent cea7db46eb
commit e1ac6209a8
1 changed files with 49 additions and 1 deletions
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@ -6,7 +6,7 @@ contributors:
- ["Árpád Goretity", "http://twitter.com/H2CO3_iOS"]
- ["Jakub Trzebiatowski", "http://cbs.stgn.pl"]
- ["Marco Scannadinari", "https://marcoms.github.io"]
- ["Zachary Ferguson", "https://github.io/zfergus2"]
---
Ah, C. Still **the** language of modern high-performance computing.
@ -630,6 +630,54 @@ typedef void (*my_fnp_type)(char *);
```
Header files are an important part of c as they allow for the connection of c
source files and can simplify code and definitions by seperating them into
seperate files.
Header files are syntaxtically similar to c source files but reside in ".h"
files. They can be included in your c source file by using the precompiler
command #include "example.h", given that example.h exists in the same directory
as the c file.
```c
/* A safe guard to prevent the header from being defined too many times. This */
/* happens in the case of circle dependency, the contents of the header is */
/* already defined. */
#ifndef EXAMPLE_H /* if EXAMPLE_H is not yet defined. */
#define EXAMPLE_H /* Define the macro EXAMPLE_H. */
/* Other headers can be included in headers and therefore transitively */
/* included into files that include this header. */
#include <string.h>
/* Like c source files macros can be defined in headers and used in files */
/* that include this header file. */
#define EXAMPLE_NAME "Dennis Ritchie"
/* Function macros can also be defined. */
#define ADD(a, b) (a + b)
/* Structs and typedefs can be used for consistency between files. */
typedef struct node
{
int val;
struct node *next;
} Node;
/* So can enumerations. */
enum traffic_light_state {GREEN, YELLOW, RED};
/* Function prototypes can also be defined here for use in multiple files, */
/* but it is bad practice to define the function in the header. Definitions */
/* should instead be put in a c file. */
Node createLinkedList(int *vals, int len);
/* Beyond the above elements, other definitions should be left to a c source */
/* file. Excessive includeds or definitions should, also not be contained in */
/* a header file but instead put into separate headers or a c file. */
#endif /* End of the if precompiler directive. */
```
## Further Reading
Best to find yourself a copy of [K&R, aka "The C Programming Language"](https://en.wikipedia.org/wiki/The_C_Programming_Language)