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# Coding style
## File format
Use [lv_misc/lv_templ.c](https://github.com/lvgl/lvgl/blob/master/src/lv_misc/lv_templ.c) and [lv_misc/lv_templ.h](https://github.com/lvgl/lvgl/blob/master/src/lv_misc/lv_templ.h)
## Naming conventions
* Words are separated by '_'
* In variable and function names use only lower case letters (e.g. *height_tmp*)
* In enums and defines use only upper case letters (e.g. *e.g. MAX_LINE_NUM*)
* Global names (API):
* starts with *lv*
* followed by module name: *btn*, *label*, *style* etc.
* followed by the action (for functions): *set*, *get*, *refr* etc.
* closed with the subject: *name*, *size*, *state* etc.
* Typedefs
* prefer `typedef struct` and `typedef enum` instead of `struct name` and `enum name`
* always end `typedef struct` and `typedef enum` type names with `_t`
* Abbreviations:
* Only words longer or equal than 6 characters can be abbreviated.
* Abbreviate only if it makes the word at least half as long
* Use only very straightforward and well-known abbreviations (e.g. pos: position, def: default, btn: button)
## Coding guide
* Functions:
* Try to write function shorter than is 50 lines
* Always shorter than 200 lines (except very straightforwards)
* Variables:
* One line, one declaration (BAD: char x, y;)
* Use `<stdint.h>` (*uint8_t*, *int32_t* etc)
* Declare variables where needed (not all at function start)
* Use the smallest required scope
* Variables in a file (outside functions) are always *static*
* Do not use global variables (use functions to set/get static variables)
## Comments
Before every function have a comment like this:
```c
/**
* Return with the screen of an object
* @param obj pointer to an object
* @return pointer to a screen
*/
lv_obj_t * lv_obj_get_scr(lv_obj_t * obj);
```
Always use `/* Something */` format and NOT `//Something`
Write readable code to avoid descriptive comments like:
`x++; /* Add 1 to x */`.
The code should show clearly what you are doing.
You should write **why** have you done this:
`x++; /*Because of closing '\0' of the string */`
Short "code summaries" of a few lines are accepted. E.g. `/*Calculate the new coordinates*/`
In comments use \` \` when referring to a variable. E.g. ``/*Update the value of `x_act`*/``
### Formatting
Here is example to show bracket placing and using of white spaces:
```c
/**
* Set a new text for a label. Memory will be allocated to store the text by the label.
* @param label pointer to a label object
* @param text '\0' terminated character string. NULL to refresh with the current text.
*/
void lv_label_set_text(lv_obj_t * label, const char * text)
{ /* Main brackets of functions in new line*/
if(label == NULL) return; /*No bracket only if the command is inline with the if statement*/
lv_obj_inv(label);
lv_label_ext_t * ext = lv_obj_get_ext(label);
/*Comment before a section */
if(text == ext->txt || text == NULL) { /*Bracket of statements start inline*/
lv_label_refr_text(label);
return;
}
...
}
```
Use 4 spaces indentation instead of tab.
You can use **astyle** to format the code. Run `code-formatter.sh` from the `scrips` folder.
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