35. Integer types <stdint.h>

The header <stdint.h> declares sets of integer types having specified widths, and defines corresponding sets of macros. It also defines macros that specify limits of integer types corresponding to types defined in other standard headers.

Types are defined in the following categories:

  • integer types having certain exact widths;
  • integer types having at least certain specified widths;
  • fastest integer types having at least certain specified widths;
  • integer types wide enough to hold pointers to objects;
  • integer types having greatest width.

(Some of these types may denote the same type.)

Corresponding macros specify limits of the declared types and construct suitable constants.

For each type described herein that the implementation provides, [1] <stdint.h> shall declare that typedef name and define the associated macros. Conversely, for each type described herein that the implementation does not provide, <stdint.h> shall not declare that typedef name nor shall it define the associated macros. An implementation shall provide those types described as “required”, but need not provide any of the others (described as “optional”).

[1]Some of these types may denote implementation-defined extended integer types.

35.1. Integer types

When typedef names differing only in the absence or presence of the initial u are defined, they shall denote corresponding signed and unsigned types as described in Types; an implementation providing one of these corresponding types shall also provide the other.

In the following descriptions, the symbol N represents an unsigned decimal integer with no leading zeros (e.g., 8 or 24, but not 04 or 048).

35.1.1. Exact-width integer types

The typedef name intN_t designates a signed integer type with width N, no padding bits and a two’s complement representation. Thus, int8_t denotes a signed integer type with a width of exactly 8 bits.

The typedef name uintN_t designates an unsigned integer type with width N. Thus, uint24_t denotes an unsigned integer type with a width of exactly 24 bits.

These types are optional. However, if an implementation provides integer types with widths of 8, 16, 32 or 64 bits, no padding bits, and (for the signed types) that have a two’s complement representation, it shall define the corresponding typedef names.

35.1.2. Minimum-width integer types

The typedef name int_leastN_t designates a signed integer type with a width of at least N, such that no signed integer type with lesser size has at least the specified width. Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.

The typedef name uint_leastN_t designates an unsigned integer type with a width of at least N, such that no unsigned integer type with lesser size has at least the specified width. Thus, uint_least16_t denotes an unsigned integer type with a width of at least 16 bits.

The following types are required:

int_least8_t   uint_least8_t
int_least16_t  uint_least16_t
int_least32_t  uint_least32_t
int_least64_t  uint_least64_t

All other types of this form are optional.

35.1.3. Fastest minimum-width integer types

Each of the following types designates an integer type that is usually fastest [2] to operate with among all integer types that have at least the specified width.

The typedef name int_fastN_t designates the fastest signed integer type with a width of at least N. The typedef name uint_fastN_t designates the fastest unsigned integer type with a width of at least N.

The following types are required:

int_fast8_t  uint_fast8_t
int_fast16_t uint_fast16_t
int_fast32_t uint_fast32_t
int_fast64_t uint_fast64_t

All other types of this form are optional.

[2]The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear grounds for choosing one type over another, it will simply pick some integer type satisfying the signedness and width requirements.

35.1.4. Integer types capable of holding object pointers

The following type designates a signed integer type with the property that any valid pointer to void can be converted to this type, then converted back to pointer to void, and the result will compare equal to the original pointer:

intptr_t

The following type designates an unsigned integer type with the property that any valid pointer to void can be converted to this type, then converted back to pointer to void, and the result will compare equal to the original pointer:

uintptr_t

These types are optional.

35.1.5. Greatest-width integer types

The following type designates a signed integer type capable of representing any value of any signed integer type:

intmax_t

The following type designates an unsigned integer type capable of representing any value of any unsigned integer type:

uintmax_t

These types are required.

35.2. Limits of specified-width integer types

The following object-like macros [3] specify the minimum and maximum limits of the types declared in <stdint.h>. Each macro name corresponds to a similar type name in Integer types.

Each instance of any defined macro shall be replaced by a constant expression suitable for use in #if preprocessing directives, and this expression shall have the same type as would an expression that is an object of the corresponding type converted according to the integer promotions. Its implementation-defined value shall be equal to or greater in magnitude (absolute value) than the corresponding value given below, with the same sign, except where stated to be exactly the given value.

[3]C++ implementations should define these macros only when __STDC_LIMIT_MACROS is defined before <stdint.h> is included.

35.2.1. Limits of exact-width integer types

  • minimum values of exact-width signed integer types

    INTN_MIN exactly \(-(2^{N-1})\)
  • maximum values of exact-width signed integer types

    INTN_MAX exactly \(2^{N-1} - 1\)
  • maximum values of exact-width unsigned integer types

    UINTN_MAX exactly \(2^N - 1\)

35.2.2. Limits of minimum-width integer types

  • minimum values of minimum-width signed integer types

    INT_LEASTN_MIN \(-(2^{N-1} - 1)\)
  • maximum values of minimum-width signed integer types

    INT_LEASTN_MAX \(2^{N-1} - 1\)
  • maximum values of minimum-width unsigned integer types

    UINT_LEASTN_MAX \(2^N -- 1\)

35.2.3. Limits of fastest minimum-width integer types

  • minimum values of fastest minimum-width signed integer types

    INT_FASTN_MIN \(-(2^{N-1} - 1)\)
  • maximum values of fastest minimum-width signed integer types

    INT_FASTN_MAX \(2^{N-1} - 1\)
  • maximum values of fastest minimum-width unsigned integer types

    UINT_FASTN_MAX \(2^N - 1\)

35.2.4. Limits of integer types capable of holding object pointers

  • minimum value of pointer-holding signed integer type

    INTPTR_MIN \(-(2^{15} - 1)\)
  • maximum value of pointer-holding signed integer type

    INTPTR_MAX \(2^{15} - 1\)
  • maximum value of pointer-holding unsigned integer type

    UINTPTR_MAX \(2^{16} - 1\)

35.2.5. Limits of greatest-width integer types

  • minimum value of greatest-width signed integer type

    INTMAX_MIN \(-(2^{63} - 1)\)
  • maximum value of greatest-width signed integer type

    INTMAX_MAX \(2^{63} - 1\)
  • maximum value of greatest-width unsigned integer type

    UINTMAX_MAX \(2^{64} - 1\)

35.3. Limits of other integer types

The following object-like macros [4] specify the minimum and maximum limits of integer types corresponding to types defined in other standard headers.

Each instance of these macros shall be replaced by a constant expression suitable for use in #if preprocessing directives, and this expression shall have the same type as would an expression that is an object of the corresponding type converted according to the integer promotions. Its implementation-defined value shall be equal to or greater in magnitude (absolute value) than the corresponding value given below, with the same sign. An implementation shall define only the macros corresponding to those typedef names it actually provides. [5]

  • limits of ptrdiff_t

    PTRDIFF_MIN \(-65535\)
    PTRDIFF_MAX \(+65535\)
  • limits of sig_atomic_t

    SIG_ATOMIC_MIN see below
    SIG_ATOMIC_MAX see below
  • limit of size_t

    SIZE_MAX \(65535\)
  • limits of wchar_t

    WCHAR_MIN see below
    WCHAR_MAX see below
  • limits of wint_t

    WINT_MIN see below
    WINT_MAX see below

If sig_atomic_t (see Signal handling <signal.h>) is defined as a signed integer type, the value of SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of SIG_ATOMIC_MAX shall be no less than 255.

If wchar_t (see Common definitions <stddef.h>) is defined as a signed integer type, the value of WCHAR_MIN shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127; otherwise, wchar_t is defined as an unsigned integer type, and the value of WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255. [6]

If wint_t (see Extended multibyte and wide character utilities <wchar.h>) is defined as a signed integer type, the value of WINT_MIN shall be no greater than -32767 and the value of WINT_MAX shall be no less than 32767; otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN shall be 0 and the value of WINT_MAX shall be no less than 65535.

35.4. Macros for integer constants

The following function-like macros [7] expand to integer constants suitable for initializing objects that have integer types corresponding to types defined in <stdint.h>. Each macro name corresponds to a similar type name in Minimum-width integer types or Greatest-width integer types.

The argument in any instance of these macros shall be a decimal, octal, or hexadecimal constant (as defined in Integer Constants) with a value that does not exceed the limits for the corresponding type.

Each invocation of one of these macros shall expand to an integer constant expression suitable for use in #if preprocessing directives. The type of the expression shall have the same type as would an expression of the corresponding type converted according to the integer promotions. The value of the expression shall be that of the argument.

[4]C++ implementations should define these macros only when __STDC_LIMIT_MACROS is defined before <stdint.h> is included.
[5]A freestanding implementation need not provide all of these types.
[6]The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended character set.
[7]C++ implementations should define these macros only when __STDC_CONSTANT_MACROS is defined before <stdint.h> is included.

35.4.1. Macros for minimum-width integer constants

The macro INTN_C (value) shall expand to an integer constant expression corresponding to the type int_leastN_t. The macro UINTN_C (value) shall expand to an integer constant expression corresponding to the type uint_leastN_t. For example, if uint_least64_t is a name for the type unsigned long long int, then UINT64_C(0x123) might expand to the integer constant 0x123ULL.

35.4.2. Macros for greatest-width integer constants

The following macro expands to an integer constant expression having the value specified by its argument and the type intmax_t:

INTMAX_C (value)

The following macro expands to an integer constant expression having the value specified by its argument and the type uintmax_t:

UINTMAX_C (value)