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Solaris Dynamic Tracing Guide
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Document Information


1.  Introduction

2.  Types, Operators, and Expressions

Identifier Names and Keywords

Data Types and Sizes


Arithmetic Operators

Relational Operators

Logical Operators

Bitwise Operators

Assignment Operators

Increment and Decrement Operators

Conditional Expressions

Type Conversions


3.  Variables

4.  D Program Structure

5.  Pointers and Arrays

6.  Strings

7.  Structs and Unions

8.  Type and Constant Definitions

9.  Aggregations

10.  Actions and Subroutines

11.  Buffers and Buffering

12.  Output Formatting

13.  Speculative Tracing

14.  dtrace(1M) Utility

15.  Scripting

16.  Options and Tunables

17.  dtrace Provider

18.  lockstat Provider

19.  profile Provider

20.  fbt Provider

21.  syscall Provider

22.  sdt Provider

23.  sysinfo Provider

24.  vminfo Provider

25.  proc Provider

26.  sched Provider

27.  io Provider

28.  mib Provider

29.  fpuinfo Provider

30.  pid Provider

31.  plockstat Provider

32.  fasttrap Provider

33.  User Process Tracing

34.  Statically Defined Tracing for User Applications

35.  Security

36.  Anonymous Tracing

37.  Postmortem Tracing

38.  Performance Considerations

39.  Stability

40.  Translators

41.  Versioning



Conditional Expressions

Although D does not provide support for if-then-else constructs, it does provide support for simple conditional expressions using the ? and : operators. These operators enable a triplet of expressions to be associated where the first expression is used to conditionally evaluate one of the other two. For example, the following D statement could be used to set a variable x to one of two strings depending on the value of i:

x = i == 0 ? "zero" : "non-zero";

In this example, the expression i == 0 is first evaluated to determine whether it is true or false. If the first expression is true, the second expression is evaluated and the ?: expression returns its value. If the first expression is false, the third expression is evaluated and the ?: expression return its value.

As with any D operator, you can use multiple ?: operators in a single expression to create more complex expressions. For example, the following expression would take a char variable c containing one of the characters 0-9, a-z, or A-Z and return the value of this character when interpreted as a digit in a hexadecimal (base 16) integer:

hexval = (c >= '0' && c <= '9') ? c - '0' :
    (c >= 'a' && c <= 'z') ? c + 10 - 'a' : c + 10 - 'A';

The first expression used with ?: must be a pointer or integer in order to be evaluated for its truth value. The second and third expressions may be of any compatible types. You may not construct a conditional expression where, for example, one path returns a string and another path returns an integer. The second and third expressions also may not invoke a tracing function such as trace() or printf(). If you want to conditionally trace data, use a predicate instead, as discussed in Chapter 1, Introduction.