---
tags:
  - C
---

In order to create a file that you can import into other C files you need to
create a header file.

> Remember that this isn't really a module since `.h` files and `#includes` are
> just text substition

In fact you create a `.h` header file which links to a `.c` file which actually
contains the code you want to import.

Let's say we want to create a "module" that handles connecting to WiFi:

```c
// wifi.h

#ifndef WIFI_H
#define WIFI_H

void wifi_connect(void);

#endif
```

In the `.h` file we just define the function signature and put checks (so it
doesn't get redefined).

Then the implementation file:

```c
// main/wifi.c

// Add any header files or auxiliary functions that the main (wifi_connect)
// function will require here

void wifi_connect(void) {}
```

Then in your main entrypoint:

```c
// main/main.c
#include "wifi.h"
wifi_connect()
```