stdint.h: Fixed-Width Integer Types

The Problem

Standard C types like int and char have size that varies by system. On one computer, int might be 2 bytes. On another, it might be 4 bytes. This is a nightmare for embedded systems like STM32!

// On PC:          int = 4 bytes
// On Arduino:     int = 2 bytes
// On old system:  int = 2 bytes

When programming microcontrollers, you need to know exactly how big your variables are.

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The Solution: stdint.h

The header file <stdint.h> provides fixed-width integer types that are always the same size:

Type	Size	Range
int8_t	1 byte	-128 to 127
uint8_t	1 byte	0 to 255
int16_t	2 bytes	-32,768 to 32,767
uint16_t	2 bytes	0 to 65,535
int32_t	4 bytes	-2.1 billion to 2.1 billion
uint32_t	4 bytes	0 to 4.2 billion

Key: The number in the type name (8, 16, 32) tells you the exact bit width.

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Why STM32 HAL Uses These

When you work with the STM32 HAL, you’ll see types like:

uint8_t button_state;      // GPIO pin value (0 or 1)
uint16_t adc_reading;      // 12-bit ADC result
uint32_t tick_count;       // Timer counter

Why?

1. Hardware registers are fixed-size - The microcontroller’s memory-mapped registers are 8, 16, or 32 bits. You need types that match exactly.

2. Portability - If you port code from STM32L476 to STM32F4, the types stay consistent.

3. No surprises - uint8_t is always 1 byte.

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Common Examples in STM32

#include "stdint.h"

// GPIO: Reading a pin (0 or 1)
uint8_t pin_state = HAL_GPIO_ReadPin(GPIOB, GPIO_PIN_2);

// ADC: Reading an analog value (12-bit: 0-4095)
uint16_t adc_value = HAL_ADC_GetValue(&hadc1);

// Timer: Getting elapsed time
uint32_t time_ms = HAL_GetTick();

// SPI/UART: Data bytes
uint8_t buffer[64];
HAL_UART_Receive(&huart2, buffer, 64, 1000);

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Quick Reference

Use these in your code:

• uint8_t - Single byte (0-255) - Most common for GPIO, SPI, UART
• uint16_t - Two bytes (0-65535) - ADC values, timer counts
• uint32_t - Four bytes - Large counts, addresses
• int8_t, int16_t, int32_t - When you need negative numbers

Avoid:

• Plain int - Size varies by system
• char - Ambiguous (is it a character or a number?)

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Summary

In embedded systems, always use stdint.h types. They guarantee the exact size you need, which prevents mysterious bugs when your code moves to a different microcontroller.

Most HAL libraries already include stdint.h, so you get these types automatically.