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PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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stdint.h(0P) POSIX Programmer's Manual stdint.h(0P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
stdint.h — integer types
#include <stdint.h>
Some of the functionality described on this reference page extends
the ISO C standard. Applications shall define the appropriate
feature test macro (see the System Interfaces volume of
POSIX.1‐2017, Section 2.2, The Compilation Environment) to enable
the visibility of these symbols in this header.
The <stdint.h> header shall declare sets of integer types having
specified widths, and shall define corresponding sets of macros.
It shall also define macros that specify limits of integer types
corresponding to types defined in other standard headers.
Note: The ``width'' of an integer type is the number of bits used
to store its value in a pure binary system; the actual type
may use more bits than that (for example, a 28-bit type
could be stored in 32 bits of actual storage). An N-bit
signed type has values in the range -2N-1 or 1-2N-1 to
2N-1-1, while an N-bit unsigned type has values in the
range 0 to 2N-1.
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,
the <stdint.h> header shall declare that typedef name and define
the associated macros. Conversely, for each type described herein
that the implementation does not provide, the <stdint.h> header
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).
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 the ISO/IEC 9899:1999 standard,
Section 6.2.5; 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 (for example, 8 or 24, but
not 04 or 048).
* 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.
The following types are required:
int8_t
int16_t
int32_t
uint8_t
uint16_t
uint32_t
If an implementation provides integer types with width 64 that
meet these requirements, then the following types are
required: int64_t uint64_t
In particular, this will be the case if any of the following
are true:
-- The implementation supports the _POSIX_V7_ILP32_OFFBIG
programming environment and the application is being built
in the _POSIX_V7_ILP32_OFFBIG programming environment (see
the Shell and Utilities volume of POSIX.1‐2017, c99,
Programming Environments).
-- The implementation supports the _POSIX_V7_LP64_OFF64
programming environment and the application is being built
in the _POSIX_V7_LP64_OFF64 programming environment.
-- The implementation supports the _POSIX_V7_LPBIG_OFFBIG
programming environment and the application is being built
in the _POSIX_V7_LPBIG_OFFBIG programming environment.
All other types of this form are optional.
* 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 int_least16_t
int_least32_t int_least64_t uint_least8_t uint_least16_t
uint_least32_t uint_least64_t
All other types of this form are optional.
* Fastest minimum-width integer types
Each of the following types designates an integer type that is
usually fastest to operate with among all integer types that
have at least the specified width.
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.
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 int_fast16_t
int_fast32_t int_fast64_t uint_fast8_t uint_fast16_t
uint_fast32_t uint_fast64_t
All other types of this form are optional.
* 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 a 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 a pointer to void, and
the result will compare equal to the original pointer:
uintptr_t
On XSI-conformant systems, the intptr_t and uintptr_t types
are required; otherwise, they are optional.
* 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.
Note:
Applications can test for optional types by using the
corresponding limit macro from Limits of Specified-Width
Integer Types.
Limits of Specified-Width Integer Types
The following macros specify the minimum and maximum limits of the
types declared in the <stdint.h> header. 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.
* 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
* 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
* 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
* 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
* 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
Limits of Other Integer Types
The following macros 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.
* 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 the <signal.h> header) 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 shall be 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 the <stddef.h> header) 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 shall be 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.
If wint_t (see the <wchar.h> header) 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 shall be 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.
Macros for Integer Constant Expressions
The following macros expand to integer constant expressions
suitable for initializing objects that have integer types
corresponding to types defined in the <stdint.h> header. Each
macro name corresponds to a similar type name listed under
Minimum-width integer types and Greatest-width integer types.
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 that is an object of the corresponding type
converted according to the integer promotions. The value of the
expression shall be that of the argument.
The argument in any instance of these macros shall be an
unsuffixed integer constant with a value that does not exceed the
limits for the corresponding type.
* Macros for minimum-width integer constant expressions
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, then
UINT64_C(0x123) might expand to the integer constant 0x123ULL.
* Macros for greatest-width integer constant expressions
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)
The following sections are informative.
None.
The <stdint.h> header is a subset of the <inttypes.h> header more
suitable for use in freestanding environments, which might not
support the formatted I/O functions. In some environments, if the
formatted conversion support is not wanted, using this header
instead of the <inttypes.h> header avoids defining such a large
number of macros.
As a consequence of adding int8_t, the following are true:
* A byte is exactly 8 bits.
* {CHAR_BIT} has the value 8, {SCHAR_MAX} has the value 127,
{SCHAR_MIN} has the value -128, and {UCHAR_MAX} has the value
255.
(The POSIX standard explicitly requires 8-bit char and two's-
complement arithmetic.)
typedef names beginning with int or uint and ending with _t may be
added to the types defined in the <stdint.h> header. Macro names
beginning with INT or UINT and ending with _MAX, _MIN, or _C may
be added to the macros defined in the <stdint.h> header.
inttypes.h(0p), signal.h(0p), stddef.h(0p), wchar.h(0p)
The System Interfaces volume of POSIX.1‐2017, Section 2.2, The
Compilation Environment
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 stdint.h(0P)
Pages that refer to this page: unistd.h(0p), wchar.h(0p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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