Export (0) Print
Expand All
10 out of 15 rated this helpful - Rate this topic

7.12 Conditional operator

Visual Studio .NET 2003

The ?: operator is called the conditional operator. It is at times also called the ternary operator.

conditional-expression:
conditional-or-expression
conditional-or-expression   ?   expression   :   expression

A conditional expression of the form b ? x : y first evaluates the condition b. Then, if b is true, x is evaluated and becomes the result of the operation. Otherwise, y is evaluated and becomes the result of the operation. A conditional expression never evaluates both x and y.

The conditional operator is right-associative, meaning that operations are grouped from right to left. For example, an expression of the form a ? b : c ? d : e is evaluated as a ? b : (c ? d : e).

The first operand of the ?: operator must be an expression of a type that can be implicitly converted to bool, or an expression of a type that implements operator true. If neither requirement is satisfied, a compile-time error occurs.

The second and third operands of the ?: operator control the type of the conditional expression. Let X and Y be the types of the second and third operands. Then,

  • If X and Y are the same type, then this is the type of the conditional expression.
  • Otherwise, if an implicit conversion (Section 6.1) exists from X to Y, but not from Y to X, then Y is the type of the conditional expression.
  • Otherwise, if an implicit conversion (Section 6.1) exists from Y to X, but not from X to Y, then X is the type of the conditional expression.
  • Otherwise, no expression type can be determined, and a compile-time error occurs.

The run-time processing of a conditional expression of the form b ? x : y consists of the following steps:

  • First, b is evaluated, and the bool value of b is determined:
    • If an implicit conversion from the type of b to bool exists, then this implicit conversion is performed to produce a bool value.
    • Otherwise, the operator true defined by the type of b is invoked to produce a bool value.
  • If the bool value produced by the step above is true, then x is evaluated and converted to the type of the conditional expression, and this becomes the result of the conditional expression.
  • Otherwise, y is evaluated and converted to the type of the conditional expression, and this becomes the result of the conditional expression.
Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft. All rights reserved.