[哲学]Lecture5.ppt

Lecture 5: Pointer to Function, Macros, Namespace Pointer to Function Example 1: Pointer to Function(cont.) Example 2: Example 3: Pointer to Function(cont.) Macros Macros are very important in C but have far fewer uses in C++. However, we still need to know it. Declaration : #define macro_name text for example: #define NAME rest of line When we write coutNAME; it will be replaced by coutrest of line; Macros(Cont.) The advantages of the macro: 1) It can improve the readability of the program. 2) It is convenient for the modification of the program. For example: #define FALSE 0 #define TRUE 1 We can write if (result==TRUE) is better than if (result==1). If we want –1 represents false, we can just write: #define FALSE -1 Macros(Cont.) Macros(Cont.) Macros(Cont.) Macros(Cont.) Macros(Cont.) Macros(Cont.) Macros(Cont.) Namespace A namespace is a mechanism for expressing logical grouping. That is, if some declarations logically belong together according to some criteria, they can be put in a common namespace to express that fact. The definition of namespace is: namespace namespace-name{ …//name declaration and definition } Namespace (cont.) Example: namespace Parser { double expr(bool) ; double prim(bool get) { /* ... */ } double term(bool get) { /* ... */ } double expr(bool get) { /* ... */ } } Namespace (cont.) However, as we know if function bodies are included in the declaration of realistically sized namespace, you typically have to wade through pages or screenfuls of information to find what services are offered. So, the best way is to separate the interface from the implementation. namespace Parser { double prim(bool) ; double term(bool) ; double expr(bool) ; } double Parser: :prim(bool get) { /* ... */ } double Parser: :term(bool get) { /* ... */ } double Parser: :expr(bool get) { /* ... */ } Qualified Names A namespace is a scope. The usual scope rules hold for namespaces, so if a name is previously d