# Invisio C Cpp Style

> Follow the Invisio MCU/DSP C coding standard for all generated and modified C/C++ code.

- Skill: `flemmingjahn2/invisio-c-cpp-style` (Agent Skill)
- Install (CLI): `npx skillmds@latest add flemmingjahn2/invisio-c-cpp-style`
- Raw SKILL.md: https://api.skillmd.com/api/skills/flemmingjahn2/invisio-c-cpp-style/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Author: flemmingJahn2 (https://skillmd.com/u/flemmingjahn2)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/flemmingjahn2/invisio-c-cpp-style

---


# Invisio C/C++ Coding Standard

## General Requirements

When generating or modifying C/C++ code:

- Follow the Invisio coding standard.
- Minimize unrelated formatting changes.
- Preserve existing external third-party code style.
- Use spaces only, never tabs.
- Indentation is 4 spaces.
- Opening braces use attached style.
- Braces are mandatory for all control statements.
- Internal functions must be declared static.
- Use const wherever applicable.
- All function arguments shall be named.
- Do not introduce new style variations.
- For session SQL workflows, available tables are: `todos`, `todo_deps`, `inbox_entries`.

## AStyle Formatting

The codebase is formatted using:

--indent=spaces=4
--suffix=.InvisioStyleErr
--keep-one-line-statements
--indent-switches
--add-braces
--style=attach
--A2
--keep-one-line-blocks

Generated code shall already conform to these rules.

## Naming Conventions

### Variables

Use camel case.

Examples:

uint16_t theRedHorse;
uint16_t readOkByte;
uint16_t readOKbyte;

### Acronyms

Acronyms are uppercase.

Examples:

UARTreadByte
UARTcomLink
UARTmask
SPIwriteByte

### Group Prefixes

When grouping is useful:

UART_readByte
UART_writeByte
SPI_readByte
SPI_writeByte

### Numbers

Numbers are written directly without underscores.

Examples:

testSPI1layer
testSPI0order
HBO0readByte

Avoid additional underscores around numbers.

## Type Naming

Use the following suffixes:

typedefName_t
structName_s
enumName_e
unionName_u

Examples:

typedef uint16_t value_t;

typedef struct {
    uint16_t value;
} settings_s;

typedef enum {
    LEFT,
    RIGHT
} position_e;

## Defines

Defines are uppercase.

#define THE_RED_HORSE (1)

Always place parentheses around define values.

Correct:

#define UART_TIMEOUT_MS (100)

Incorrect:

#define UART_TIMEOUT_MS 100

## Doxygen Comments

### File Header

/**
 * @file the_read_horse.c
 *
 * Description if applicable
 */

### Function Declaration

/**
 * Function
 *
 * @param in   pointer to input
 * @param out  pointer to output
 *
 * @ingroup groupName
 */
void function(uint16_t *in, uint16_t *out);

### Single-Line Doxygen

/// Description
#define THEREDHORSE (1)

or

#define THEREDHORSE (1)  ///< Description

## Header File Structure

Order shall be:

1. Doxygen file comment
2. Include guard
3. Includes
4. File-wide defines
5. Typedefs
6. Structures
7. Global variable declarations using extern
8. Function declarations
9. End include guard

Example:

#ifndef THE_RED_HORSE_H_
#define THE_RED_HORSE_H_

#include "typedef.h"

#define MAX_COUNT (10)

typedef uint16_t counter_t;

extern uint16_t globalCounter;

void readData(uint16_t *buffer);

#endif // THE_RED_HORSE_H_

## Source File Structure

Order shall be:

1. Doxygen file comment
2. Includes
3. Defines
4. Typedefs
5. Structures
6. Global variables
7. Internal function declarations
8. Function definitions

Do not place extern declarations in .c files.

## Functions

Internal functions must be static.

static uint16_t calculateChecksum(uint16_t value);

Use const when applicable.

static uint16_t calculateChecksum(const uint8_t *buffer,
                                  uint16_t length);

Example:

uint16_t readData(uint16_t in1, uint16_t in2) {
    uint16_t i = 0;

    if (i == 0) {
        /* code */
    } else {
        /* code */
    }

    i++;

    return i;
}

## Control Statements

Braces are always required.

Correct:

if (condition) {
    action();
}

Incorrect:

if (condition)
    action();

One-line blocks are allowed:

if ((timerClockFreq == 64000000) && (baudRate == 115200)) { timerPeriodTimesOnePointFive = 675; return; }

## Boolean Conditions

Conditions must evaluate explicitly to a Boolean expression.

Incorrect:

while (count)

Correct:

while (count != 0)

Correct:

if (enabled == TRUE)

## For Loops

for (i = 0; i < 10; i++) {
    /* code */
}

## While Loops

while (condition) {
    /* code */
}

do {
    /* code */
} while (condition);

## Switch Statements

Use indented cases.

Always include a default case.

Default shall be last.

Fall-through is not allowed when executable code exists between cases.

switch (condition) {
    case ABC:
    case DEF:
        doSomething();
        break;

    case XYZ:
        doSomethingElse();
        break;

    default:
        handleError();
        break;
}

## Expressions

Examples:

a += (c + d);

a = (a + b) / (c * d);

strp->field = str.fl - ((x & MASK) >> DISP);

Do not mix unrelated data types on the same expression line.

## Pointer Style

Correct:

uint16_t *s;
uint16_t *t;
uint16_t *u;

Correct:

uint16_t *s, *t, *u;

Incorrect:

uint16_t* s, t, u;

## Enums

typedef enum {
    LEFT    = 0,     ///< Left
    RIGHT   = 1      ///< Right
} position_e;

## Structs

typedef struct {
    uint16_t var1;
    uint16_t var2;
} structName_s;

## Strings

Reserve space for the NULL terminator explicitly.

uint8_t myString[10 + 1];

## Global Variables

- Avoid direct access when possible.
- Provide wrapper functions for read-only access.
- Use extern only in header files.
- Never place static variables in header files.

## File and Folder Names

- Spaces are not allowed.
- Use the project's camel-case naming rules.
- Matching .c and .h files shall be located in the same folder.
- Group related files into folders when appropriate.

## External Code

When importing external source files:

- Preserve the original code style.
- Do not reformat external code.

When copying snippets into project files:

- Convert the snippet to Invisio style.
- Add a comment indicating the original source.