unsigned char limited to 127 on osx lion?

Question

I am facing a strange issue, working on my mac osx lion (under xcode4/clang, though it is reproducible with gcc4.2).

It seems, that I can not assign any value above 127 for a unsigned char variable. So, when I assign

v = (unsigned char) 156;

or, simply

std::cout << (unsigned char) 231 << std::endl;

my program does not produce any output.

When I run this code

std::cout << "Unsigned chars range up to " << UCHAR_MAX << std::endl;

I get the following output:

Unsigned chars range up to 255

However, when I run something like this, the program generates outputs up to some different arbitrary value (such as c = 114, c = 252, etc etc) each time. for(unsigned char c = 0; c < CHAR_MAX; c++) std::cout << "c = " << 2*c << std::endl;

Changing the CHAR_MAX to UCHAR_MAX, the program ends without an output again :(

Thanks in advance

Answer 1

cout is converting the numeric value to a character from the character set (Well, it's attempting to ... when you don't see anything it's not a valid character for your charset, and technically it's the terminal that's deciding this).

Cast it to unsigned int instead.

Edit to add: ildjarn makes a very valid point in his comment to your question; if you ran this in the debugger you'd see that the value was indeed what you expected.

Answer 2

What symbol are you expecting to see to represent character (unsigned char)231? On most systems, these are extended characters that need special terminal settings to be displayed as anything coherent if even visible.

Try this:

unsigned char testChar = (unsigned char)231;
unsigned int testInt = (unsigned int)testChar;
std::cout << testInt << std::endl;

Answer 3

The value of unsigned char is not limited to 127, however standard ASCII is only 7 bits (so 128 values). Any value above 127 does not represent any character (unless you use some kind of extended ASCII), so nothing is printed.