Module dev.civl.abc
Package dev.civl.abc.ast.node.IF.expression

Interface CharacterConstantNode

All Superinterfaces:
ASTNode, ConstantNode, ExpressionNode, ForLoopInitializerNode, InitializerNode, SizeableNode
public interface CharacterConstantNode extends ConstantNode

An instance of this interface represents a single Unicode character occurring as a literal element in a C program.

Following the information in the C11 Standard, the C11 representation of a character literal is interpreted to yield (1) a Unicode character, and (2) a C type. Both pieces of information are included in an instance of this class.

Character constants are discussed in Section 6.4.4.4 of C11. They have a complex structure.

First, there is a possible prefix: either none, L, u, or U.

Second there is a sequence of "c-char" (enclosed in single quotes).

A c-char is either (1) any member of the source character set other than single-quote, backslash, or newline, or (2) an escape sequence.

An escape sequence is either a simple escape sequence, an octal escape sequence, a hexadecimal escape sequence, or a universal character name.

A simple escape sequence is one of the following: 

 \'  \"  \?  \\  \a  \b  \f  \n  \r  \t  \v

An octal escape sequence is a backslash followed by 1, 2, or 3 octal digits.

A hexadecimal escape sequence consists of \x followed by 1 or more hexadecimal digits.

Note: it seems that if the sequence of c-char has length greater than one, the behavior is implementation-defined, so we are only going to support sequences of length 1.

Types:

The type is determined from the prefix as follows: int (none), wchar_t (L), char16_t (u ), or char32_t (U). wchar_t is an integer type, described in C11 Sec. 7.19. char16_t and char32_t are described in Sec. 7.28; the first is the smallest unsigned integer type with a width of at least 16; the latter is the smallest unsigned integer type with a width of at least 32.

If there is no prefix, the constant is known as an "integer character constant", otherwise it is a "wide character constant".

Note: the type may be null until it is set. This is because the special types (wchar_t, etc.) are not known until typedefs have been processed.

Values:

This part is very confusing and certainly some of it is implementation-dependent. The procedure outlined here seems to be consistent with what is written in the Standard.

For an integer character constant, the procedure is as follows. The code point (which is a non-negative integer) must lie in the range of the type unsigned char. (If not, an exception is thrown.) It is then converted to a value of type char as follows: if the range of char coincides with that of unsigned char, nothing to do. Otherwise, if the value already lies within the range of signed char, nothing to do. Otherwise, subtract (unsignedCharMax+1) from value. Finally, the char value is converted to a value of type int.

Example: if char = unsigned char and has 8 bits, this will yield an int value in the range [0,255]. '\xFF' yields the int value 255.

Example: If char=signed char and has 8 bits and two's complement representation is used for integers, then the int value will lie in the range [-128,127]. '\xFF' yields the int value -1 (255-256=-1).

For wide character constants, the value is determined by one of the functions mbtowc, mbrtoc16, or mbrtoc32. For now, we punt on wide characters.