2820. Clarify <cstdint> macros

Section: 21.4 [cstdint] Status: Open Submitter: Thomas Köppe Opened: 2016-11-12 Last modified: 2017-10-22

Priority: 3

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I would like clarification from LWG regarding the various limit macros like INT_8_MIN in <cstdint>, in pursuit of editorial cleanup of this header's synopsis. I have two questions:

  1. At present, macros like INT_8_MIN that correspond to the optional type int8_t are required (unconditionally), whereas the underlying type to which they appertain is only optional. Is this deliberate? Should the macros also be optional?

  2. Is it deliberate that C++ only specifies sized aliases for the sizes 8, 16, 32 and 64, whereas the corresponding C header allows type aliases and macros for arbitrary sizes for implementations that choose to provide extended integer types? Is the C++ wording more restrictive by accident?

[2017-01-27 Telecon]

Priority 3

[2017-03-04, Kona]

C11 ties the macro names to the existence of the types. Marshall to research the second question.

Close 2764 as a duplicate of this issue.

[2017-03-18, Thomas comments and provides wording]

This is as close as I can get to the C wording without resolving part (a) of the issue (whether we deliberately don't allow sized type aliases for sizes other than 8, 16, 32, 64, a departure from C). Once we resolve part (a), we need to revisit <cinttypes> and fix up the synopsis (perhaps to get rid of N) and add similar wording as the one below to make the formatting macros for the fixed-width types optional. For historical interest, this issue is related to LWG 553 and LWG 841.

[2016-07, Toronto Saturday afternoon issues processing]

Status to Open

Previous resolution: [SUPERSEDED]

This wording is relative to N4640.

  1. Append the following content to 21.4.1 [cstdint.syn] p2:

    -2- The header defines all types and macros the same as the C standard library header <stdint.h>. In particular, for each of the fixed-width types (int8_t, int16_t, int32_t, int64_t, uint8_t, uint16_t, uint32_t, uint64_t) the type alias and the corresponding limit macros are defined if and only if the implementation provides the corresponding type.

[2017-10-21, Thomas Köppe provides improved wording]

Proposed resolution:

This wording is relative to N4687.

  1. Change 21.4.1 [cstdint.syn], header <cstdint> synopsis, as indicated:

    using int64_t = signed integer type; // optional
    using intN_t = see below; // optional, see below
    using int_fast64_t = signed integer type;
    using int_fastN_t = see below; // optional, see below
    using int_least64_t = signed integer type;
    using int_leastN_t = see below; // optional, see below
    using uint64_t = unsigned integer type; // optional
    using uintN_t = see below; // optional, see below
    using uint_fast64_t = unsigned integer type;
    using uint_fastN_t = see below; // optional, see below
    using uint_least64_t = unsigned integer type;
    using uint_leastN_t = see below; // optional, see below
    using uintmax_t = unsigned integer type;
    using uintptr_t = unsigned integer type; // optional
    #define INT_N_MIN  see below;
    #define INT_N_MAX  see below;
    #define UINT_N_MAX  see below;
    #define INT_FASTN_MIN  see below;
    #define INT_FASTN_MAX  see below;
    #define UINT_FASTN_MAX  see below;
    #define INT_LEASTN_MIN  see below;
    #define INT_LEASTN_MAX  see below;
    #define UINT_LEASTN_MAX  see below;
    #define INTMAX_MIN  see below;
    #define INTMAX_MAX  see below;
    #define UINTMAX_MAX  see below;
    #define INTPTR_MIN  see below;
    #define INTPTR_MAX  see below;
    #define UINTPTR_MAX  see below;
    #define PTRDIFF_MIN  see below;
    #define PTRDIFF_MAX  see below;
    #define SIZE_MAX  see below;
    #define SIGATOMIC_MIN  see below;
    #define SIGATOMIC_MAX  see below;
    #define WCHAR_MIN  see below;
    #define WCHAR_MAX  see below;
    #define WINT_MIN  see below;
    #define WINT_MAX  see below;
    #define INTN_C(value)  see below;
    #define UINTN_C(value)  see below;
    #define INTMAX_C(value)  see below;
    #define UINTMAX_C(value)  see below;

    -1- The header also defines numerous macros of the form:

    INT_[FAST LEAST]{8 16 32 64}_MIN
    [U]INT_[FAST LEAST]{8 16 32 64}_MAX

    plus function macros of the form:

    [U]INT{8 16 32 64 MAX}_C

    -2- The header defines all types and macros the same as the C standard library header <stdint.h>. See also: ISO C 7.20

    -?- In particular, all types that use the placeholder N are optional when N is not 8, 16, 32 or 64. The exact-width types intN_t and uintN_t for N = 8, 16, 32, 64 are also optional; however, if an implementation provides integer types with the corresponding width, no padding bits, and (for the signed types) that have a two's complement representation, it defines the corresponding typedef names. Only those macros are defined that correspond to typedef names that the implementation actually provides. [Note: The macros INTN_C and UINTN_C correspond to the typedef names int_leastN_t and uint_leastN_t, respectively. — end note]

  2. Change 30.12.2 [cinttypes.syn] as indicated:

    #define PRIdNN see below
    #define PRIiNN see below
    #define PRIoNN see below
    #define PRIuNN see below
    #define PRIxNN see below
    #define PRIXNN see below
    #define SCNdNN see below
    #define SCNiNN see below
    #define SCNoNN see below
    #define SCNuNN see below
    #define SCNxNN see below
    #define PRIdLEASTNN see below
    #define PRIiLEASTNN see below
    #define PRIoLEASTNN see below
    #define PRIuLEASTNN see below
    #define PRIxLEASTNN see below
    #define PRIXLEASTNN see below
    #define SCNdLEASTNN see below
    #define SCNiLEASTNN see below
    #define SCNoLEASTNN see below
    #define SCNuLEASTNN see below
    #define SCNxLEASTNN see below
    #define PRIdFASTNN see below
    #define PRIiFASTNN see below
    #define PRIoFASTNN see below
    #define PRIuFASTNN see below
    #define PRIxFASTNN see below
    #define PRIXFASTNN see below
    #define SCNdFASTNN see below
    #define SCNiFASTNN see below
    #define SCNoFASTNN see below
    #define SCNuFASTNN see below
    #define SCNxFASTNN see below

    -1- The contents and meaning of the header <cinttypes> […]

    -?- In particular, macros that use the placeholder N are defined if and only if the implementation actually provides the corresponding typedef name in 21.4.1 [cstdint.syn], and moreover, the fscanf macros are provided unless the implementation does not have a suitable fscanf length modifier for the type.