Is there some c++ proposal for Integer literal for fixed width integer types like this?
// i's type is unsigned int
auto i = 10u;
// j's type is uint32_t
auto j = 10u32;
1 Answer
Yes: P1280R0 Integer Width Literals (published 2018-10-05).
It proposes the following literals:
namespace std::inline literals::inline integer_literals {
constexpr uint64_t operator ""u64 (unsigned long long arg);
constexpr uint32_t operator ""u32 (unsigned long long arg);
constexpr uint16_t operator ""u16 (unsigned long long arg);
constexpr uint8_t operator ""u8 (unsigned long long arg);
constexpr int64_t operator ""i64 (unsigned long long arg);
constexpr int32_t operator ""i32 (unsigned long long arg);
constexpr int16_t operator ""i16 (unsigned long long arg);
constexpr int8_t operator ""i8 (unsigned long long arg);
}
And its update P1280R1 that "Modifies return types to actually be [u]int_leastXX_t and friends. This is to make sure that we are actually replacing the [U]INTxx_C macros, as these return a [u]int_leastXX_t":
namespace std::inline literals::inline integer_literals {
constexpr uint_least64_t operator ""u64 (unsigned long long arg);
constexpr uint_least32_t operator ""u32 (unsigned long long arg);
constexpr uint_least16_t operator ""u16 (unsigned long long arg);
constexpr uint_least8_t operator ""u8 (unsigned long long arg);
constexpr int_least64_t operator ""i64 (unsigned long long arg);
constexpr int_least32_t operator ""i32 (unsigned long long arg);
constexpr int_least16_t operator ""i16 (unsigned long long arg);
constexpr int_least8_t operator ""i8 (unsigned long long arg);
}
There is a 2019-06-12 update P1280R2 that makes the literals consteval instead of constexpr.
Status update
I found this issue tracking the paper: https://github.com/cplusplus/papers/issues/153
The latest update is
Jul 19, 2019
Discussed in LEWG in Cologne - http://wiki.edg.com/bin/view/Wg21cologne2019/P1280
Forward to LWG for C++23.
SF F N A SA 0 0 3 7 4 Dropping, barring additional revision from the author discussing the points raised in the discussion.
the table represents number of votes: (strongly) for / neutral / (strongly) against
And in this Cologne 2019 LEWG Summary the resolution of the paper is "Discussed but not Approved nor Forwarded"
10 Comments
RiaD
fwiw, I think that update made it worse. If I write
auto x = 5u32; I want a 32bit integer and not "maybe something else that will fail on other platform"
Pete Becker
@RiaD -- it's
uint32_t that will fail on some other platform. uint_least32_t is always available; uint32_t won't exist on (admittedly unusual) platforms that don't have a native 32-bit integer type. That's an inherent ambiguity with fixed-size integer types: you might want an exact size, or you might want something large enough to hold some number of bits.RiaD
@PeteBecker 1) "platform doesn't support uint32, so I won't compile 5u32" is straightforward compiler error 2) "in some random place where uint_least32_t is used, some overloading is now ambiguous" (suppose that uint32_least_t=unsigned long long and the same example will be broken as in P1280) is less straight forward. I of course agree that you might want uint32_least_t, but why not use 5u_least32 ?
plugwash
And does multiplying two large
uint16_ts and storing the result in a uint16_t variable result in wraparound or undefined behavior? Integer math in C/C++ is a horrible mess.
bolov
@MarkRansom update on the answer. Sadly it looks like it's dropped
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INT8_C(127),UINT16_C(65535),UINT32_C(10).