<stdint.h> provides fixed-width integer types (C99): int8_t, uint32_t, int64_t, etc., guaranteeing exact widths across platforms. Also includes intmax_t, intptr_t, and limit macros like INT32_MAX.

Use fixed-width types for binary I/O, hardware registers, and portable low-level code.

This example queries the sizes of fixed-width integer types on the platform.

// compile: gcc -o stdintexample stdintexample.c
// run: ./stdintexample
// description: show fixed-width integer type sizes
 
#include <stdint.h>
#include <stdio.h>
 
int main() {
    printf("int8_t = %zu bytes\n", sizeof(int8_t));
    printf("int16_t = %zu bytes\n", sizeof(int16_t));
    printf("int32_t = %zu bytes\n", sizeof(int32_t));
    printf("int64_t = %zu bytes\n", sizeof(int64_t));
    printf("intptr_t = %zu bytes\n", sizeof(intptr_t));
    printf("INT32_MAX = %d\n", INT32_MAX);
    printf("UINT64_MAX = %llu\n", (unsigned long long)UINT64_MAX);
 
    return 0;
}

Fixed-width signed integers:

• int8_t, int16_t, int32_t, int64_t: exactly N-bit signed integers
• Guaranteed to exist and have exactly that size

Fixed-width unsigned integers:

• uint8_t, uint16_t, uint32_t, uint64_t: exactly N-bit unsigned integers

Pointer-sized integers:

• intptr_t, uintptr_t: guaranteed to hold any pointer safely
• Use for pointer arithmetic without losing information

Widest types:

• intmax_t, uintmax_t: widest signed and unsigned integers on platform
• May be 64-bit or larger (e.g., 128-bit on some platforms)

Min/max macros (INT8_MIN through INT64_MIN, etc.):

• INT8_MAX, INT8_MIN: ±128 for int8_t
• INT16_MAX, INT16_MIN: ±32,767 for int16_t
• INT32_MAX, INT32_MIN: ±2,147,483,647 for int32_t
• INT64_MAX, INT64_MIN: ±9,223,372,036,854,775,807 for int64_t
• UINT8_MAX, UINT16_MAX, UINT32_MAX, UINT64_MAX: unsigned limits
• INTPTR_MAX, UINTPTR_MAX: pointer limits
• INTMAX_MAX, UINTMAX_MAX: widest type limits

Common usage:

• Use fixed-width types (uint32_t, etc.) for binary data, network protocols, hardware interfaces
• Prefer int, unsigned for general integer arithmetic (these have efficient operations)
• This header is more portable than <limits.h> for specific-width guarantees