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ICMAKE Part 2

Issue 2

From Issue #2
April-May 1994

Apr 01, 1994  By Frank B. Brokken and K. Kubat
 in
In part 1, Brokken and Kubat explained where the ideas for icmake came from, the basics of the program and where you can get a copy. In Part 2 we cover the grammar of icmake source files. The final part of this article will appear next month and will show examples of the use of icmake.
4.4.4. Expressions and operators

Icmake allows a large number of operators to form or combine expressions. Binary operators may be used with the following operand-types:

operand-types

  1. Each binary operator must be used with two variables or constants of the same type, e.g., the addition of an int and a string is not allowed; icmake performs no default type casting.

  2. Some operators may not be used with some types, e.g., string subtraction is not allowed, but string addition is.

  3. The operators have a certain priority; some operators are evaluated before others. The priority of operators is identical to the priority used by C.

The binary operators recognized by icmake are summarized in the following table:

binary operators

All binary operators with the exception of the assignment operators are left-associative. The assignment operators are right-associative. The operators at the top of the table have the lowest priority; those at the bottom have the highest priority. Operators with different priority are separated by lines.

The unary operators are summarized in the following table. The unary operators have higher priority than binary operators and are right-associative. The exception is the expression-nesting operator, which surrounds an expression and does not associate.

unary operators

4.4.4.1. Logical operators

Icmake recognizes three logical operators: the logical and (&&), the logical or (||) and the logical not (!). These operators can be used to combine or reverse logical expressions.

The logical not operator reverses the logical outcome of an expression. The logical and operator and the logical or operator group conditions. Icmake evaluates a combined condition using these operators until the outcome of the condition is determined, in analogy to C:

  1. In the condition (c1 && c2), c2 is not evaluated if c1 yields zero, since when c1 yields zero the combined condition can only fail. Therefore, c2 is evaluated only if c1 yields not zero.

  2. In the condition (c1 || c2), c2 is not evaluated if c1 yields not zero, since when c1 yields not zero the combined condition can only succeed. Therefore, c2 is only evaluated if c1 yields zero.

Logical operators may be used with any type of expression. An int constant or variable yields its integer representation. A string constant or variable yields not zero when the length of the string is non-zero; e.g., string “a” yields not zero.

A list or variable yields not zero when the number of strings in the list is not zero, e.g., in the following code fragment the making process is stopped when no files with extension “.c” are found:

list

to be continued...

Look for part 3 of 4 of the IC Make Article in the next issue of Linux Journal.

______________________

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