C Standard Library<stdint.h>

<stdint.h>Is a header file introduced by the C99 standard. It provides definitions for several integer types that have explicit size and signedness attributes, ensuring consistency across different platforms.

<stdint.h>The library is intended to address the issue of inconsistent integer type sizes across different platforms in C, thereby improving code portability and maintainability.

<stdint.h>Primarily used to define fixed-size integer types, the minimum/maximum values of integer types, and type qualifiers for integer types. This avoids relying on compiler- or OS platform-specific integer sizes.

<stdint.h>By providing fixed-width integer types and related macros, programmers can explicitly specify the required integer size without relying on platform implementation details.

<stdint.h>The main purpose is:

  • Provide fixed-width integer types (such asint8_t、int16_tetc.), ensuring that their sizes are consistent across different platforms.

  • Define platform-independent integer types (such asint_least8_t、int_fast16_tetc.), used to optimize performance and memory usage.

  • Provide maximum-width integer types (such asintmax_t、uintmax_t), used to represent the largest possible integer.

Fixed-width integer types

These types explicitly specify their width (number of bits), ensuring that they have the same size across different platforms.

Type Description
int8_t 8-bit signed integer
int16_t 16-bit signed integer
int32_t 32-bit signed integer
int64_t 64-bit signed integer
uint8_t 8-bit unsigned integer
uint16_t 16-bit unsigned integer
uint32_t 32-bit unsigned integer
uint64_t 64-bit unsigned integer

Note：

  • If a platform does not support a particular fixed-width type, that type will not be defined.

Minimum-width integer types

These types have at least the specified width, but may be larger.

Type Description
int_least8_t Signed integer of at least 8 bits
int_least16_t Signed integer of at least 16 bits
int_least32_t Signed integer of at least 32 bits
int_least64_t Signed integer of at least 64 bits
uint_least8_t Unsigned integer of at least 8 bits
uint_least16_t Unsigned integer of at least 16 bits
uint_least32_t Unsigned integer of at least 32 bits
uint_least64_t Unsigned integer of at least 64 bits

Fastest minimum-width integer types

These types are the fastest integer types with the specified width, typically used for performance optimization.

Type Description
int_fast8_t Fastest signed integer of at least 8 bits
int_fast16_t Fastest signed integer with at least 16 bits
int_fast32_t Fastest signed integer with at least 32 bits
int_fast64_t Fastest signed integer with at least 64 bits
uint_fast8_t Fastest unsigned integer of at least 8 bits
uint_fast16_t Fastest unsigned integer with at least 16 bits
uint_fast32_t Fastest unsigned integer with at least 32 bits
uint_fast64_t Fastest unsigned integer with at least 64 bits

Maximum-width integer types

These types are used to represent the largest possible integer values.

Type Description
intmax_t Signed integer of maximum width
uintmax_t Unsigned integer of maximum width

Pointer-width integer types

These types are used to represent integers of pointer size.

Type Description
intptr_t Signed integer capable of holding a pointer
uintptr_t Unsigned integer capable of holding a pointer

Macro definition

<stdint.h>It also defines macros for representing the maximum and minimum values of specific types.

Macro Description
INT8_MIN int8_tminimum value of
INT8_MAX int8_tmaximum value of
UINT8_MAX uint8_tmaximum value of
INT16_MIN int16_tminimum value of
INT16_MAX int16_tmaximum value of
UINT16_MAX uint16_tmaximum value of
INT32_MIN int32_tminimum value of
INT32_MAX int32_tmaximum value of
UINT32_MAX uint32_tmaximum value of
INT64_MIN int64_tminimum value of
INT64_MAX int64_tmaximum value of
UINT64_MAX uint64_tmaximum value of
INTMAX_MIN intmax_tminimum value of
INTMAX_MAX intmax_tmaximum value of
UINTMAX_MAX uintmax_tmaximum value of

Example

The following is a use of<stdint.h>example:

Example

#include <stdio.h>
#include <stdint.h>

int main() {
    // Fixed-width integer types
    int32_t a = 100;
    uint64_t b = 1000000000000ULL;

    // Minimum-width integer types
    int_least16_t c = 200;

    // Fastest minimum-width integer types
    int_fast32_t d = 300;

    // Maximum-width integer types
    intmax_t e = INTMAX_MAX;

    // Output value
    printf("a = %d\n", a);
    printf("b = %llu\n", b);
    printf("c = %d\n", c);
    printf("d = %d\n", d);
    printf("e = %jd\n", e);

    return 0;
}

Notes

  • <stdint.h>Only available in C99 and later versions.

  • Fixed-width types (such asint32_t) may not be available on some platforms; therefore, you should check whether it is defined before use.

  • Usage<stdint.h>It can improve code portability, especially in scenarios that require precise control over integer sizes.

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