1.函数类型

int Inc(int a)
{
    return a+1;
}
int Add_Int(int a,int b)//函数的类型 返回类型+形参列表
{
    return a+b;
}
int Mul_Int(int x,int y)
{
    return x*y;
}
int main()
{
    int fun(int,int);
    int (*pfun)(int,int);
    int (*pfun)(int,int)=NULL
    return 0;
}

int Inc(int a)
{
    return a+1;
}
int Add_Int(int a,int b)
    return a+b;
}
int Mul_Int(int x,int y)
{
    return x*y;
}
int main()
{
	int x = 10, y = 20, z = 0;
	Add_Int(x,y);	// call 
	Add_Int; //不调用函数，函数的地址
}

3.函数指针

int Inc(int a)
{
    return a+1;
}
int Add_Int(int a,int b)
    return a+b;
}
int Mul_Int(int x,int y)
{
    return x*y;
}
int main()
{
	int x = 10, y = 20, z = 0;
	int (*pfun)(int, int) = NULL;//函数地址

	pfun = Add_Int;


	pfun = Mul_Int;

	sizeof(pfun);  // 4
	//sizeof(*pfun);

	//pfun = pfun + 1; // void * ;

	return 0;
}

4.调用

函数指针不能进行加一操作

int Inc(int a)
{
    return a+1;
}
int Add_Int(int a,int b)
    return a+b;
}
int Mul_Int(int x,int y)
{
    return x*y;
}
int main()
{
	int x = 10, y = 20, z = 0;
	int (*pfun)(int, int) = NULL;

	pfun = Add_Int;

	z = (*pfun)(x, y);

	z = pfun(x, y);


	pfun = Mul_Int;

	z = (*pfun)(x, y);
	z = pfun(x, y);

	return 0;
}

函数名不一样，但是返回类型和形参类型一样，就可以实现函数指针通用

5.函数指针作为形参使用

int Inc(int a)
{
    return a+1;
}
int Add_Int(int a,int b)
    return a+b;
}
int Mul_Int(int x,int y)
{
    return x*y;
}
void Print(int x, int y, int (*pfun)(int, int))
{
	if (pfun != NULL)
	{
		int z = pfun(x, y);  // int z = (*pfun)(x,y);
		printf("%d \n", z);
	}
}
int main()
{
	int x = 10, y = 20;
	Print(x, y, Add_Int);

	Print(x, y, Mul_Int);
	return 0;
}

6.无类型函数指针通用性

void* Pint(const void* p)
{
	int* ip = (int*)p;
	printf("%d ", *ip);
	return (ip + 1);
}
void* Pdouble(const void* p)
{
	double* dp = (double*)p;
	printf("%f ", *dp);
	return (dp + 1);
}
void* Pchar(const void* p)
{
	char* cp = (char*)p;
	printf("%c ", *cp);
	return (cp + 1);
}
void Print_Ar(void* ar, int n, void* (*fpun)(const void*))
{
	for (int i = 0; i < n; ++i)
	{
		ar = fpun(ar);
	}
	printf("\n");
}
int main()
{
	int ar[] = { 12,23,34,45,56,67 };
	int in = sizeof(ar) / sizeof(ar[0]);

	double dx[] = { 1.2,2.3,3.4,4.5,5.6,6.7,7.8,8.9 };
	int dn = sizeof(dx) / sizeof(dx[0]);

	char str[] = { 'a','k','a','s','h','i' };
	int cn = sizeof(str) / sizeof(str[0]);

	Print_Ar(ar, in, Pint);
	Print_Ar(dx, dn, Pdouble);
	Print_Ar(str, cn, Pchar);

	return 0;
}

7.不同数据处理

void qsort(void* ptr,size_t count,size_t size,int ( * comp)(const void* ,const void *))

int IntComp(const void* arg1, const void* arg2)
{
	const int* p1 = (const int* )arg1;
	const int* p2 = (const int* )arg2;
	if (*p1 > *p2) return 1;
	else if (*p1 < *p2) return -1;
	else return 0;
}
int DouComp(const void* arg1, const void* arg2)
{
	const double* p1 = (const double* )arg1;
	const double* p2 = (const double* )arg2;
	if (*p1 > *p2) return 1;
	else if (*p1 < *p2) return -1;
	else return 0;
}
int main()
{
	int ar[] = { 56,34,12,89,90,100,45,78,67 };
	int in = sizeof(ar) / sizeof(ar[0]);

	double dr[] = { 5.6,3.4,1.2,8.9,9.0,10.0,4.5,7.8,6.7 };
	int dn = sizeof(dr) / sizeof(dr[0]);
	qsort(ar, in, sizeof(int), IntComp);

	qsort(dr, dn, sizeof(double), DouComp);
	return 0;
}

字符串

int StrComp(const void* arg1, const void* arg2)
{
	const char* sp1 = *(const char**)arg1;
	const char* sp2 = *(const char**)arg2;

	return strcmp(sp1, sp2);

}
int main()
{
	const char* str[] = { "akashi","huming","newdata","print","const","wang" };
	int n = sizeof(str) / sizeof(str[0]);
	qsort(str, n, sizeof(char*), StrComp);
	return 0;
}

结构体

struct Student
{
	char s_name[16];
	int s_age;
};	
int StudComp(const void* arg1, const void* arg2)
{
	const struct Student* sp1 = (const struct Student*)arg1;
	const struct Student* sp2 = (const struct Student*)arg2;
	//if (sp1->s_age > sp2->s_age) return -1;
	//else if (sp1->s_age < sp2->s_age) return 1;
	//else return 0;

	return strcmp(sp2->s_name, sp1->s_name);

}
int main()
{
	struct Student stud[] = { "akashi",19,"huming",23,"wang",16,"zhang",18,"linan",29 };
	int n = sizeof(stud) / sizeof(stud[0]);
	qsort(stud, n, sizeof(struct Student), StudComp);

	return 0;
}

8.typedef与函数指针

int Add(int a, int b)
{
	return a + b;
}

typedef int (*PFUN)(int, int);

int (*g_fun)(int, int) = NULL;

 
PFUN fun(PFUN p)
{
	int* old = g_fun;
	g_fun = p;
	return old;
}
int main()
{

	int x = 10, y = 20, z = 0;
	z = Add(x, y);
	z = (*(int (*)(int, int))0x00401020)(x, y);
	z = ((PFUN)0x00401020)(x, y);
	(*(void(*)())0)();
	return 0;

}

int Add(int a, int b) { return a + b; }
int Mul(int a, int b) { return a * b; }
int Sub(int a, int b) { return a - b; }

typedef int(*PFUN)(int, int);

int main()
{
	int (*pfun[3])(int, int) = { Add,Mul,Sub };

	PFUN ar[3] = { Add,Mul,Sub };
	return 0;
}