3.9.1 Fundamental types
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 (3.9); 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.

2 There are four signed integer types: “signed char”, “short int”, “int”, and “long int.” In this list, each type provides at least as much storage as those preceding it in the list. Plain ints have the natural size suggested by the architecture of the execution environment(39) ; the other signed integer types are provided to meet special needs.
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39) that is, large enough to contain any value in the range of INT_MIN and INT_MAX, as defined in the header <climits>.

Originally Posted by vmanes

What you're asking about is defined (or not specifically defined) in the C++ standards. Size of an int should be the natural size of the achitecture - many of us grew up with 2-byte ints. The standards don't prescribe specifics, it's more on the order of any larger data type must be at least as large as that that comes before it. Thus, today you see that int and long int are generally the same size.

Originally Posted by Narue

>I have heard that in C++ a char is always 1 byte
Yes. Or to be more specific, "char" and "byte" are synonymous terms, and sizeof(char) is guaranteed to be 1.

>and an integer is always 4 bytes on any machine
Nope. The size of an integer is at least 16 bits, but it can be whatever the implementation chooses as long as the basic requirements for type relations are met.

>its weird that 1 byte can still be 1 byte even if
>the type consists of 16 bits instead of 8 @_@.
It's not weird at all when you understand that "byte" is an abstraction for the smallest addressable unit. An octet (the 8-bit entity you're familiar with) is one such concrete implementation of this abstraction.

>I wanted to see if there was some header or implementation
>that defined the way bytes were mapped for each type
The closest you can get is looking in <limits.h>. CHAR_BIT will tell you how many bits are in a byte, and the *MIN/*MAX values will give you an idea of how other types are structured on your system. You can find out the minimum requirements by looking at a suitable draft of the C standard. Example.