Skip to main content

Documentation Index

Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt

Use this file to discover all available pages before exploring further.

The ?: operator, formally known as the conditional operator, is the only ternary operator in the C programming language. It evaluates a controlling scalar expression and, based on whether the result compares unequal to zero, evaluates and yields the value of exactly one of two subsequent expressions. 
logical_OR_expression ? expression_if_true : expression_if_false

​
Evaluation Semantics

  1. Control Expression: The first operand (logical_OR_expression) must have a scalar type (arithmetic or pointer). It is evaluated first.
  2. Sequence Point: There is a strict sequence point immediately after the evaluation of the first operand. All side effects of the first operand are guaranteed to be complete before any further evaluation occurs.
  3. Short-Circuit Evaluation: The operator guarantees mutually exclusive evaluation of the second and third operands. If the first operand evaluates to a non-zero value, only expression_if_true is evaluated. If the first operand evaluates to zero, only expression_if_false is evaluated. The unevaluated operand produces no side effects.

​
Type Resolution

The type of the result yielded by the conditional operator is determined at compile-time by the types of the second and third operands, regardless of which expression is evaluated at runtime. The compiler determines the common type using the following rules:
  • Arithmetic Types: If both the second and third operands have arithmetic types, the usual arithmetic conversions are applied to determine a common type. For example, if one is int and the other is double, the result type of the entire expression is double.
  • Structure and Union Types: If both operands have compatible structure or union types, the result has that compatible structure or union type.
  • Void Types: If both operands are void expressions, the result is a void expression.
  • Pointer Types:
    • If both are pointers to compatible types, the result is a pointer to the composite type, carrying the combined type qualifiers (e.g., const, volatile) of both operands.
    • If one operand is a pointer and the other is a null pointer constant (like NULL or 0), the result type is the type of the pointer operand.
    • If one operand is a pointer to an object type and the other is a pointer to void, the result is a pointer to an appropriately qualified version of void. The resulting pointer type combines the type qualifiers of both the object pointer and the void pointer.

​
Value Category

In C, the result of the conditional operator is always an rvalue (a value that does not have a memory address identifiable by the programmer). Unlike in C++, you cannot use the C conditional operator on the left side of an assignment operator. 
/* Valid C: Yields an rvalue */
int result = (x > y) ? x : y;

/* Invalid C: Attempting to use the result as an lvalue */
((x > y) ? x : y) = 10; /* Compilation error */
Master C with Deep Grasping Methodology!Learn More