How do I specify an integer literal of type unsigned char in C++?

Question

I can specify an integer literal of type unsigned long as follows:

const unsigned long example = 9UL;

How do I do likewise for an unsigned char?

const unsigned char example = 9U?;

This is needed to avoid compiler warning:

unsigned char example2 = 0;
...
min(9U?, example2);

I'm hoping to avoid the verbose workaround I currently have and not have 'unsigned char' appear in the line calling min without declaring 9 in a variable on a separate line:

min(static_cast<unsigned char>(9), example2);

I changed your question slightly to what i think your intention was. Things like `10` are called "literals" in C++ (while being called "constants" in C). It's more common to C++ folks and avoids confusion with declaration of "example". — Johannes Schaub - litb, Feb 21 '10 at 14:32

score 69 · Accepted Answer · answered Apr 25 '16 at 08:57

69

C++11 introduced user defined literals. It can be used like this:

inline constexpr unsigned char operator "" _uchar( unsigned long long arg ) noexcept
{
    return static_cast< unsigned char >( arg );
}

unsigned char answer()
{
    return 42;
}

int main()
{
    std::cout << std::min( 42, answer() );        // Compile time error!
    std::cout << std::min( 42_uchar, answer() );  // OK
}

answered Apr 25 '16 at 08:57

10

OP, make this the accepted answer already! Though I'd advise using just `_uc`, for conciseness as well as parity with the standard `ul` and so on. – underscore_d Nov 02 '17 at 20:15

Michael Burr · Answer 2 · 2010-02-21T07:28:42.130

32

C provides no standard way to designate an integer constant with width less that of type int.

However, stdint.h does provide the UINT8_C() macro to do something that's pretty much as close to what you're looking for as you'll get in C.

But most people just use either no suffix (to get an int constant) or a U suffix (to get an unsigned int constant). They work fine for char-sized values, and that's pretty much all you'll get from the stdint.h macro anyway.

edited Feb 21 '10 at 07:28

answered Feb 21 '10 at 07:12

Michael Burr

333,147
50
533
760

3

As of glibc 2.26, UINT8_C doesn't give you a 8 bit integer: ```# define UINT8_C(c) c``` – Chih-Hsuan Yen Feb 10 '18 at 15:58

score 26 · Answer 3 · answered Feb 21 '10 at 08:32

26

You can cast the constant. For example:

min(static_cast<unsigned char>(9), example2);

You can also use the constructor syntax:

typedef unsigned char uchar;
min(uchar(9), example2);

The typedef isn't required on all compilers.

answered Feb 21 '10 at 08:32

janm

17,976
1
43
61

I think you are the only one that decrypted his pretty secret question correctly. Firstly, i didn't figure out either what he really wanted to ask. – Johannes Schaub - litb Feb 21 '10 at 13:44
Right, that is my current work around, with this question I was hoping to avoid the cast, but it sounds like the answer is there is no literal that will allow me to avoid the cast. – WilliamKF Feb 21 '10 at 16:07
with the constructor syntax, does this cause an object allocation every time as opposed to the literal? – Ravi Nankani Nov 29 '16 at 03:19
@RaviNankani It's a constructor syntax for a primitive type, so there is should be no overhead. – janm Nov 29 '16 at 05:43
2

I'd write something like this (as the **uint8_t** typedef has been part of the standard since C++11): `min(uint8_t{9}, example2);` – dan_din_pantelimon Dec 07 '17 at 03:27

score 16 · Answer 4 · answered Dec 02 '11 at 10:09

16

If you are using Visual C++ and have no need for interoperability between compilers, you can use the ui8 suffix on a number to make it into an unsigned 8-bit constant.

min(9ui8, example2);

You can't do this with actual char constants like '9' though.

answered Dec 02 '11 at 10:09

Mr Lister

45,515
15
108
150

score 11 · Answer 5 · answered Feb 21 '10 at 07:43

11

Assuming that you are using std::min what you actually should do is explicitly specify what type min should be using as such

unsigned char example2 = 0;
min<unsigned char>(9, example2);

answered Feb 21 '10 at 07:43

E.M.

4,498
2
23
30

score 3 · Answer 6 · answered Feb 21 '10 at 04:16

3

Simply const unsigned char example = 0; will do fine.

answered Feb 21 '10 at 04:16

Kyle Lutz

7,966
2
20
23

1

That's an `int` literal, implicitly cast down to a unsigned char (const), isn't it? – Scott Smith Dec 18 '20 at 23:57

score 1 · Answer 7 · answered Feb 21 '10 at 04:18

1

I suppose '\0' would be a char literal with the value 0, but I don't see the point either.

answered Feb 21 '10 at 04:18

Axel Gneiting

5,293
25
30

2

This is not unsigned char, but signed char. – WilliamKF Feb 21 '10 at 05:10
14

@WilliamKF: the type of `'\0'` in C++ is neither `signed char` not `unsigned char`, it is `char` as Axel says. `char` is unlike other integral types: `signed int` and `int` are the same type, but `signed char` and `char` are not. – Steve Jessop Feb 21 '10 at 12:27
I thought `char` was implicitly the same as `signed char`, but I may be thinking of C... – Scott Smith Dec 18 '20 at 23:59
2

@ScottSmith, it's the same thing in C, also three distinct types. It's implementation defined if `char` is signed or unsigned. – Bo R Mar 05 '21 at 09:43

score 0 · Answer 8 · answered Feb 21 '10 at 04:25

0

There is no suffix for unsigned char types. Integer constants are either int or long (signed or unsigned) and in C99 long long. You can use the plain 'U' suffix without worry as long as the value is within the valid range of unsigned chars.

answered Feb 21 '10 at 04:25

user261840

168
2

score -3 · Answer 9 · answered Apr 11 '16 at 16:45

-3

The question was how to "specify an integer 'literal' of type unsigned char in C++?". Not how to declare an identifier.

You use the escape backslash and octal digits in apostrophes. (eg. '\177')

The octal value is always taken to be unsigned.

answered Apr 11 '16 at 16:45

Clive

269
1
14

No it's not taken to be unsigned, it's still `char` — neither `unsigned char` nor `signed char`. – Ruslan Jan 13 '17 at 11:16

How do I specify an integer literal of type unsigned char in C++?

9 Answers9

Linked

Related