#### 结构体 ```c struct student { const char *name; const char *address; int age; }; ``` struct student表示一个类型,类似于int,声明和初始化,以及使用如下: ```c #include <stdio.h> #include <string.h> struct student { const char *name; const char *address; int age; }; int main(int argc, char const *argv[]) { struct student person = {"wuzhc", "Guangzhou", 18}; printf("%s\n", person.name); return 0; } ``` #### typeof别名 可以为结构体设置别名,如下 ```c typedef struct student { const char *name; const char *address; int age; } stu; ``` 其中结构体名可以省略,如下: ```c typedef struct { const char *name; const char *address; int age; } stu; ``` #### 结构体复制 当一个结构体变量赋值给另一个结构体变量时,计算机会创建一个全新的副本,如果结构体含有指针,那么复制的仅仅是指针的值,如下: #### 嵌套结构 ```c #include <stdio.h> #include <string.h> typedef struct { const char *subject; int score; } report; typedef struct { const char *name; const char *address; int age; report card; // 这是一个嵌套结构体 } stu; int main(int argc, char const *argv[]) { stu person = {"wuzhc", "Guangzhou", 18, {"english", 59}}; printf("%s\n", person.card.subject); return 0; } ``` #### 结构体指针 类似于其他类型指针,代码如下: ```c void modifyAge(stu *s) { s->age = 23; // 等价于(*s).age = 23 } ``` #### 联合union 当定义联合时,计算机会为最大的字段分配空间,如php的zend_value如下: ```c typedef union _zend_value { zend_long lval; //int整形 double dval; //浮点型 zend_refcounted *counted; zend_string *str; //string字符串 zend_array *arr; //array数组 zend_object *obj; //object对象 zend_resource *res; //resource资源类型 zend_reference *ref; //引用类型，通过&$var_name定义的 zend_ast_ref *ast; //下面几个都是内核使用的value zval *zv; void *ptr; zend_class_entry *ce; zend_function *func; struct { uint32_t w1; uint32_t w2; } ww; } zend_value; ``` 初始化: ```c zend_value zv = {.dval=1.5} ``` #### 枚举 关键字enum,定义如下: ```c typeof enum { COUNT, POUNDS, PINTS } unit; ``` #### 位字段 用位字段主要用于减少占用空间,如定义一个结构如下: ```c typedef struct { unsigned int fist_visit:1; unsigned int come_age:1; unsigned int fingers_lost:4; unsigned int days_a_week:3; } survey; ``` 位字段应当声明为unsigned int;只有出现在同一个结构中,位字段才能节省空间 #### 位字段和数值计算 最大值 = 2^位数 - 1,即4位只能保存0到15的值 #### demo ```c #include <stdio.h> #include <string.h> // 枚举 typedef enum { PREPATE_TYPE, HOMEWORK_TYPE, SCANEXAM_TYPE } sourceType; // 联合 typedef union { short count; short weight; } quantity; // 结构体 typedef struct { const char *subject; int score; } report; // 结构体 typedef struct { const char *name; const char *address; int age; report card; // 这是一个嵌套结构体 sourceType type; quantity q; } stu; // 位字段 typedef struct { unsigned int fist_visit:1; unsigned int come_age:1; unsigned int fingers_lost:4; unsigned int days_a_week:3; } survey; // 结构体指针 void modifyAge(stu *s) { s->age = 23; // 等价于(*s).age = 23 } int main(int argc, char const *argv[]) { stu person = {"wuzhc", "Guangzhou", 18, {"english", 59}, HOMEWORK_TYPE, {.weight=118}}; if (person.type == HOMEWORK_TYPE) { printf("%s\n", "homework"); } else { printf("%s\n", "other"); } modifyAge(&person); printf("%i\n", person.age); printf("%i\n", person.q); return 0; } ```