struct

struct是一组数据元素一个名字，这些数据元素，作为成员，可以有不同类型和不同长度。C++声明struct语法如下：

struct structure_name {

member_type1 member_name1;

member_type2 member_name2;

member_type3 member_name3;

.

.

} object_names;

简单示例如下:

struct product {
   int weight; float price; } ; product apple; product banana, melon;

声明struct并定义多个实例:

struct product {
   int weight; float price; } apple, banana, melon;

完整struct例子:

// example about structures #include 
     
       #include 
      
        #include 
       
         using namespace std; struct movies_t {
   string title; int year; } mine, yours; void printmovie (movies_t movie); int main () {
   string mystr;   mine.title = "2001 A Space Odyssey";   mine.year = 1968;   cout << "Enter title: ";   getline (cin,yours.title);   cout << "Enter year: ";   getline (cin,mystr);   stringstream(mystr) >> yours.year;   cout << "My favorite movie is:\n ";   printmovie (mine);   cout << "And yours is:\n ";   printmovie (yours); return 0; } void printmovie (movies_t movie) {
     cout << movie.title;   cout << " (" << movie.year << ")\n"; }
       
      
     

 

struct和指针

struct movies_t {
   string title; int year; }; movies_t amovie; movies_t * pmovie; pmovie = &amovie;

完整示例如下:

// pointers to structures #include 
     
       #include 
      
        #include 
       
         using namespace std; struct movies_t {
   string title; int year; }; int main () {
   string mystr;   movies_t amovie;   movies_t * pmovie;   pmovie = &amovie;   cout << "Enter title: ";   getline (cin, pmovie->title);   cout << "Enter year: ";   getline (cin, mystr);   (stringstream) mystr >> pmovie->year;   cout << "\nYou have entered:\n";   cout << pmovie->title;   cout << " (" << pmovie->year << ")\n"; return 0; }
       
      
     

 

内部struct

struct movies_t {
   string title; int year; }; struct friends_t {
   string name; string email;   movies_t favorite_movie;   } charlie, maria; friends_t * pfriends = &charlie;

使用如下:

charlie.name maria.favorite_movie.title charlie.favorite_movie.year pfriends->favorite_movie.year

union

union允许以不同的数据类型访问相同的内存，因为他们实际上是在内存中的相同位置,它的声明和struct差不多，但功能完全不同:

union union_name {
     member_type1 member_name1;   member_type2 member_name2;   member_type3 member_name3;   .   . } object_names;

union声明的所有元素在内存中占有相同的物理空间,其大小是该声明的最大元素的大小:

union mytypes_t {
   char c; int i; float f;   } mytypes;

 

每一个不同的数据类型。由于所有的元素都指的是内存中的同一位置，修改的内容之一，会影响其他元素的内容。

 

匿名union

struct和正常union

struct {
   char title[50]; char author[50];   union {
   float dollars; int yen;   } price; } book;

struct和匿名union

struct {
   char title[50]; char author[50];   union {
   float dollars; int yen;   }; } book;

第一种类型的访问方式，如下:

book.price.dollars book.price.yen

第二种类型的访问方式,如下:

book.dollars book.yen

 

enum

  定义枚举类型的基本语法：

enum enumeration_name {  value1,  value2,  value3,  .  .} object_names;

例如:

enum Week {SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY};

其中SUNDAY = 0,MONDAY = 1……SATURDAY = 6。也就是说，第１个枚举值代表0，第2个枚举值代表1，这样依次递增1。

也可以在定义时，直接指定某个或某些枚举值的数值,例如:

enum Week {MONDAY = 1,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY,SUNDAY};

其中MONDAY等于1，这样，TUESDAY就将等于2，直接到SUNDAY等于7。

 

声明枚举变量:

Week today = TUESDAY;

 

枚举值，我们就称为格举常量，因为它一经定义以后，就不可再改变，以下用法是错误的！

TUESDAY = 10; //错误！我们不能改变一个枚举值的数值。