Precedence and Associativity in Programming

In programming, the order of operations is crucial for correctly evaluating expressions. Operator precedence and associativity play a critical role in determining this order.

Who Defines Operator Precedence and Associativity?

The standard for the specific programming language defines operator precedence and associativity. For C and C , these definitions can be found in the respective language grammars.

How is Operator Precedence Defined?

Operator precedence establishes the grouping of operators based on their priority. Operators with higher precedence are evaluated before those with lower precedence. This hierarchy is defined within the language grammar.

How is Associativity Defined?

Associativity determines how adjacent uses of the same operator are grouped. For instance, if an operator is left-to-right associative, adjacent uses of that operator associate from left to right. This rule is also derived from the language grammar.

Relation to Order of Evaluation

Operator precedence and associativity do not directly control the order of evaluation for function calls. The standard only requires that the operands of an operator be evaluated before the operator itself.

Left-to-Right Function Associativity

The belief that functions always evaluate from left to right is not entirely accurate. While some operators, such as the function call operator, do have left-to-right associativity, this does not dictate the order in which function calls are evaluated.

Impact of Associativity

Consider the example f1() f2() * f3(). The * operator has higher precedence than the operator, so the expression groups as f1() (f2() * f3()). However, the order of evaluating the function calls is not specified by associativity.

Other Sequence Considerations

Specific operators can impose sequencing restrictions on operand evaluation. For instance, in x || y, x is always evaluated before y. This allows for short-circuiting behaviors.

Historical Context

Sequence points were previously used in C and C to define evaluation order. However, modern standards have adopted the concept of "sequenced before" relationships to describe this behavior.