C Fixed Width Integers

C Fixed Width Integers

C Fixed Width Integers were introduced in C99 to ensure variables always have a predictable size (in bits), regardless of system or compiler differences.

For example, on one system an int may be 2 bytes (16-bit) while on another it may be 4 bytes (32-bit).
Fixed-width types solve this problem.

These types are defined in:

Exact-Width Integer Types

These guarantee that the variable is exactly the specified number of bits.

Type	Signed Version	Unsigned Version	Size
8-bit	`int8_t`	`uint8_t`	1 byte
16-bit	`int16_t`	`uint16_t`	2 bytes
32-bit	`int32_t`	`uint32_t`	4 bytes
64-bit	`int64_t`	`uint64_t`	8 bytes

Example:

Minimum and Fastest Integer Types

Minimum-width types

Guaranteed to be at least the specified width.

Signed	Unsigned
`int_least8_t`	`uint_least8_t`
`int_least16_t`	`uint_least16_t`
`int_least32_t`	`uint_least32_t`
`int_least64_t`	`uint_least64_t`

Fastest integer types

Optimized for speed (may be larger than required).

Signed	Unsigned
`int_fast8_t`	`uint_fast8_t`
`int_fast16_t`	`uint_fast16_t`
`int_fast32_t`	`uint_fast32_t`
`int_fast64_t`	`uint_fast64_t`

Special Type: `intptr_t` and `uintptr_t`

These are integer types that guaranteed to hold a pointer address.

Useful in embedded systems and low-level programming.

Format Specifiers (from `inttypes.h`)

For portable printing, you should include:

Examples:

Example: Using All Fixed Integer Types

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>int main() {
uint8_t age = 25;
int16_t temp = -300;
uint32_t id = 100000;
int64_t population = 7800000000;

printf("Age: %" PRIu8 "\n", age);
printf("Temperature: %" PRId16 "\n", temp);
printf("ID: %" PRIu32 "\n", id);
printf("Population: %" PRId64 "\n", population);

return 0;
}

#include <stdio.h>

#include <stdint.h>

#include <inttypes.h>int main() {

uint8_t age = 25;

int16_t temp = -300;

uint32_t id = 100000;

int64_t population = 7800000000;

printf("Age: %" PRIu8 "\n", age);

printf("Temperature: %" PRId16 "\n", temp);

printf("ID: %" PRIu32 "\n", id);

printf("Population: %" PRId64 "\n", population);

return 0;

}

🧠 Why Use Fixed-Width Integers?

Benefit	Reason
Portability	Same size across platforms
Predictable memory usage	Important in embedded systems
Binary communication	Networking, file formats require exact size
Performance	Optimized fixed-width data for microcontrollers

Summary

Group	Example Types	Purpose
Exact-width	`int8_t`, `uint32_t`	Same size on any system
Minimum-width	`int_least16_t`	At least specified size
Fastest-width	`int_fast32_t`	Best performance
Pointer-compatible	`intptr_t`	Store pointer as integer

C Fixed Width Integers