Re: [Boost-users] [proto] char vs. int behaviour when matching

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"Dominique" == Dominique Devienne writes:

Dominique> On Wed, Sep 2, 2009 at 3:51 PM, Eric Niebler wrote: >> That's where you're mistaken. char, signed char and unsigned char >> are 3 distinct types. Dominique> Hi Eric. After learning about int "abcd" literals from Dominique> your mpl::string post, I'm now learning about an integral Dominique> type which is neither signed nor unsigned! Dominique> (sounds like my assumption that char is an integral type Dominique> might be wrong in fact...) Dominique> Would you mind expanding a little on this, possibly with Dominique> pointers to further info please? They are defined as different types in the standard. What may be more surprising is that given: void foo (int); void foo (signed char); void foo (unsigned char); char a; foo (a) -> invokes foo (int). This is because being different types they are not particularly related and each is promoted to int (unless a perfect match is found, of course). Here's a fragment I've grabbed from the web, don't know if it is for C or C++: 3.9.1 Fundamental types [basic.fundamental] 1 Objects declared as characters char) shall be large enough to store any member of the implementation's basic character set. If a character from this set is stored in a character object, the integral value of that character object is equal to the value of the single character literal form of that character. It is implementation-defined whether a char object can hold negative values. Characters can be explicitly declared unsigned or signed. Plain char, signed char, and unsigned char are three distinct types. A char, a signed char, and an unsigned char occupy the same amount of storage and have the same alignment requirements (basic.types); that is, they have the same object representation. For character types, all bits of the object representation participate in the value representation. For unsigned character types, all possible bit patterns of the value representation represent numbers. These requirements do not hold for other types. In any particular implementation, a plain char object can take on either the same values as a signed char or an unsigned char; which one is implementation-defined. --