第8章 变量的作用域和生存期.ppt

Chapter 8 Topics Local Scope vs. Global Scope of an Identifier Detailed Scope Rules to Determine which Variables are Accessible in a Block Determining the Lifetime of a Variable Writing a Value-Returning Function for a Task Some Value-Returning Functions with Prototypes in Header Files cctype and cmath Creating and Using a Module Structure Chart Stub Testing a Program Scope of Identifier the scope of an identifier (or named constant) means the region of program code where it is legal to use that identifier for any purpose Local Scope vs. Global Scope the scope of an identifier that is declared inside a block (this includes function parameters) extends from the point of declaration to the end of the block the scope of an identifier that is declared outside of all namespaces, functions and classes extends from point of declaration to the end of the entire file containing program code Detailed Scope Rules Function name has global scope. Function parameter scope is identical to scope of a local variable declared in the outermost block of the function body. Global variable (or constant) scope extends from declaration to the end of the file, except as noted in rule 5. Local variable (or constant) scope extends from declaration to the end of the block where declared. This scope includes any nested blocks, except as noted in rule 5. An identifier’s scope does not include any nested block that contains a locally declared identifier with the same name (local identifiers have name precedence). Name Precedence Implemented by Compiler Determines Scope When an expression refers to an identifier, the compiler first checks the local declarations. If the identifier isn’t local, compiler works outward through each level of nesting until it finds an identifier with same name. There it stops. Any identifier with the same name declared at a level further out is never reached. If compiler reaches global declarations and still can’t find the id