C++: how do I convert hex char to unsigned char?

Question

I have a method that takes unsigned chars, but I want to pass it 0x01.

I know I can represent hex chars in strings by going "\x01"... but that is still a signed char.

EDIT: some code:

kennys_hash((unsigned char const *)"\x00"); // the method call

the error:

src/main.cpp:88: error: invalid conversion from ‘const unsigned char*’ to ‘unsigned char’ src/main.cpp:88: error: initializing argument 1 of ‘unsigned char kennys_hash(unsigned char)’

the method header:

unsigned char kennys_hash(unsigned char out)

ALso, when the cast is just to unsigned char, I get this error:

src/main.cpp:88: error: cast from ‘const char*’ to ‘unsigned char’ loses precision

Can you be more specific? What is your input, what your desired output? Please provide code. — Björn Pollex
– Björn Pollex, Commented Mar 24, 2011 at 15:01
"\x00" is not char. its char*. it doesn't match "unsigned char out" — Shelwien
– Shelwien, Commented Mar 24, 2011 at 15:12
there's no sense to cast a pointer to a char. make it kennys_hash( "\x00"[0] ); or something — Shelwien
– Shelwien, Commented Mar 24, 2011 at 15:16

unwind · Accepted Answer · 2011-03-24 15:06:35Z

3

0x01 is the same as 1, which is positive, and thus it doesn't matter if it's considered to be signed or unsigned, the value is the same.

If you want to have an unsigned type on the literal, use 0x01u.

answered Mar 24, 2011 at 15:06

unwind

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1 Comment

NullVoxPopuli Over a year ago

By using 0x01u, I can completely forget about strings altogether!~ thanks!

Sjoerd · Accepted Answer · 2011-03-24 15:13:10Z

Note that "\x00" is an string constant (read: array of char), and not a single character constant.

Use single quotes: '\x00' is a character constant.

The type might be char, but that is automatically converted to unsigned char when needed. Some compilers might issue a warning though.

Björn Pollex · Accepted Answer · 2011-03-24 15:17:23Z

1

You can use boost::lexical_cast:

unsigned char bar = boost::lexical_cast<unsigned char>( "\x71" );

answered Mar 24, 2011 at 15:17

Björn Pollex

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Comments

Erik · Accepted Answer · 2011-03-24 15:06:12Z

0

void foo(unsigned char const * u); ... foo( (unsigned char const *) "\x01");

answered Mar 24, 2011 at 15:06

Erik

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Comments

harald · Accepted Answer · 2011-03-24 15:07:06Z

You can pass it an array of unsigned chars, like this:

unsigned char data[5] = {1, 2, 3, 4, 5}; func_that_takes_unsigned_chars(data, sizeof data);

Naruto77 · Accepted Answer · 2011-03-24 15:10:01Z

I bet you can't send it \x-01. Therefore you are sending it an unsigned int.

You can always test you your input before you send it to the func. If inp < 0 then send it back.

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