9.3 结构体 枚举 typedef

#include <stdio.h>
#include <string.h>
struct STU
{
	char sex;
	int id;
};
int main()
{
	struct STU s1;
	memset(&s1, 0, sizeof(s1));   //把结构体内存清零
	s1.id = 0x12345678;
	s1.sex = 0x88;
}

struct STU
{
        int id;        // 4字节对齐
        char name[10];
};

struct STU
{
        char id;      //最长字节就是char  1个字节
        char name[10];
};

struct STU
{
        short id;
        char name[10];
};

struct STU
{
	char * id;          // 4
	char name[10];      // 12        4字节对齐
};

struct STU
{
        char id : 2; // 代表 id  是两个 bit 长  
};

#include <stdio.h>
#include <string.h>
struct STU
{
        char id : 2;     //两个bit位     如果存4的话就会是0  如果存5的话就会是1
};
int main()
{
        struct STU s1;
        s1.id = 4;
        printf("%d\n" , s1.id);
}

struct STU
{
        char id : 2;
        char name : 2;
};

struct STU
{
        int id : 2;
};

struct STU
{
        int id : 2;
        int age : 2;
};

#include <stdio.h>
#include <string.h>
struct A
{
        int i;
        char c;
};
struct B
{
        int i;
        struct A a;
};
int main()
{
        printf("%d\n" , sizeof(struct B));
}

#include <stdio.h>
#include <string.h>
struct STU
{
        char name[1024];
};
int main()
{
        struct STU s1 = { "liuwei" };
        struct STU s2;
        s2 = s1;             // memcpy( &s2 , &s1 , sizeof(s1));     和这句话效果一样
        printf("%s\n",s2.name);
}

#include <stdio.h>
#include <string.h>
struct STU
{
        char *name;
};
int main()
{
        struct STU s1 = { "liuwei" };
        struct STU s2;
        s2 = s1;
        s1.name = "xuanyuan";
        printf("%s\n",s2.name);
}

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct STU
{
        char *name;
};
int main()
{
        struct STU s1 , s2;
        s1.name = malloc(10);
        strcpy(s1.name , "liuwei");
        s2 = s1;
        strcpy(s1.name , "xuanyuan");
        printf("%s\n",s2.name);
        free(s1.name);
}

#include <stdio.h>
#include <string.h>
struct str
{
        char buf[1024];
};
struct str get_str()
{
        struct str s;
        strcpy( s.buf , "hello world");
        return s;
}
int main()
{
        struct str tmp = get_str();      //返回的是一个结构体变量，结构体变量之间的赋值，是内存拷贝
        printf("%s\n" , tmp.buf);
        return 0;
}

#include <stdio.h>
#include <string.h>
char *get_str()
{
        char buf[100];
        strcpy( buf , "hello world" );
        return buf;
}
int main()
{
        printf("%s\n" , get_str() );  //输出乱码，因为buf的地址已经被函数释放了
        return 0;
}

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct str
{
        char buf[1024];
};
struct str *get_str()
{
        struct str *s = malloc(sizeof( struct str ));
        strcpy( s->buf , "hello world");
        return s;
}
int main()
{
        struct str *tmp = get_str();
        printf("%s\n" , tmp->buf);
        free(tmp);
        return 0;
}

#include <stdio.h>
#include <string.h>
struct str
{
        char buf[1024];
};
struct str *get_str()
{
        struct str s;
        strcpy( s.buf , "hello world");
        return &s;          //虽然返回的是结构体的地址，但是结构体的内存是在栈上，函数结束被释放
}
int main()
{
        struct str *tmp = get_str();
        printf("%s\n" , tmp->buf);
        return 0;
}

#include <stdio.h>
int main()
{
        enum color{ red = 11 , yellow = 10 , blue};
        printf("%d\n",blue);
        return 0;
}

typedef const char *(*FUNC)( const char *str1 , const char *str2 );