Miscellaneous Operators

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Epsilon User's Manual and Reference > Epsilon Extension Language > Expressions >

Miscellaneous Operators

expression:
        expression ? expression : expression
        expression , expression
        expression [ expression ]
        expression -> identifier
        expression . identifier

The conditional operator ? : has three operands. The first operand is always evaluated first. If nonzero, the second operand is evaluated, and that is the value of the result. Otherwise, the third operand is evaluated, and that is the value of the result. Exactly one of the second and third operands is evaluated. The first operand may be a number, spot, or pointer. The second and third operands may either both be numbers, both spots, both pointers to the same type of object, or one may be a pointer or spot and the other the constant zero. In the first case the result is an int, and in the last two cases the result is a spot or a pointer of the same type.

The , operator first evaluates its first argument and throws away the result. It then evaluates its second argument, and the result has that value and type. In any context where a comma has a special meaning (such as in a list of arguments), EEL assumes that any commas it finds are used for that special meaning.

The [ ] operator is EEL's subscripting operator. Because of the special way that addition of a pointer and a number works, we can define the subscripting operator in terms of other operators. The expression e1[e2] is the same as *((e1)+(e2)), and since addition is commutative, also the same as e2[e1]. In practice, subscripting works in the expected way. Note that the first object in an array has subscript 0, however. One of the operands must be a pointer and the other a number. The type of the result is that of the pointed-to object.

The . operator disassembles structures or unions. Its operand is an lvalue which is a structure or union. After the . an identifier naming one of the operand's members must appear. The result is an lvalue referring to that member.

The -> operator is an abbreviation for a dereference (unary *) followed by a member selection as above. Its operand is a pointer to a structure or union, and it is followed by the name of one of the structure's or union's members. The result is an lvalue referring to that member. The expression strptr->membername is the same as the expression (*strptr).membername.

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