C - 基础 - 联合、枚举、typedef、函数指针

联合

#include <stdio.h>

union hold{
	int digit;
	double big;
	char letter;
};
struct cat {
	char miao[10];
};
struct dog {
	char wang[10];
};
union data {
	struct cat my_cat;
	struct dog my_dog;
};
// 联合的用法：将多个类型放在同一个结构中，使用状态区别
struct my_pet
{
	int status; // 0:cat , 1:dog
	union data pet;
};

int main(int argc, char *argv[])
{
	// 联合只存储一个值
	union hold valA;
	valA.letter = 'A';

	union hold valB = valA;
	union hold valC = { 88 };			// 初始化digit成员
	union hold valD = { .big = 10.00 }; //指定初始化成员
	// 联合与结构的访问方式相同
	return 0;
}

枚举

#include <stdio.h>

enum color { red, yellow = 10, green, blue };
int main(int argc, char *argv[])
{
	printf("red: %d ,yellow: %d ,green: %d , \n", red, yellow, green);
	int c = 11;
	switch (c)
	{
	case red: puts("oh red.\n"); break;
	case yellow: puts("oh yellow.\n"); break;
	case green: puts("oh green.\n"); break;
	case blue: puts("oh blue.\n"); break;
	default:
		puts("这枚举还没数组好用 坑.\n");
		break;
	}
	return 0;
}

typedef声明

#include <stdio.h>

typedef unsigned char BYTE;
typedef char * STRING; // char指针
typedef struct book {	// 可省去结构标记
	char *	title;
	double value;
} MYBOOK;
int main(int argc, char *argv[])
{
	BYTE x = 'A';
	STRING ss = "you are beautiful";
	printf("typedef BYTE en . %c %s \n", x,ss);
	MYBOOK mb = {
		"aaa",10.01
	};
	printf("mb is %s \n", mb.title);
	return 0;
}

函数与指针

#include <stdio.h>
#include <ctype.h>

void to_upper(char *);
void to_lower(char *);
void show(void(*fp)(char *), char * str); //第一个参数为指向函数的指针
int main(int argc, char *argv[])
{
	char name[10] = "AAaa";
	void(*funcp)(char *);	// 函数指针的定义、赋值
	funcp = to_upper;
	show(funcp, name);      // 传递函数指针
	funcp = to_lower;
	show(funcp, name);
	return 0;
}

void to_upper(char * str)
{
	while (*str)
	{
		*str = toupper(*str);
		str++;
	}
}

void to_lower(char * str)
{
	while (*str)
	{
		*str = tolower(*str);
		str++;
	}
}

void show(void(*fp)(char *), char * str)
{
	(*fp)(str);		//函数指针的使用 fp(str)亦可
	printf("str is : %s \n", str);
}