C语言讲义——指针函数和函数指针

指针函数

返回值是指针的函数，如void* malloc(...)

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int *newAdd(int a, int b); // 声明指针函数

main() {
	int *p1 = NULL;
	p1 = newAdd(1, 2);
	printf("p1 = 0x%x 
", p1);
	printf("*p1 = %d 
", *p1);
	getchar();
}

int *newAdd(int a, int b) {
	int *p = (int *)malloc(sizeof(int));
	memset(p, 0, sizeof(int));
	printf("   函数内:p = 0x%x 
", p);

	*p = a + b;
	printf("   函数内:*p = %d 
", *p);

	return p;
}

函数中创建“数组”

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int *createArray(int n) {
    int *p = (int *)malloc(n * sizeof(int));
    memset(p, 0, n * sizeof(int));
    int *q = p;
    for(int  i = 0 ; i<n; i++) {
        *(q++) = i*i;
    }
    return p;
}
main() {
    int *p = NULL;
    p = createArray(10);
    int *q = p;
    while(p-q<10) {
        printf("%d ", *p);
        p++;
    }
    //TODO:释放内存
}

函数指针

指向函数的指针

#include<stdio.h>
int addition(int x,int y) {
	return (x+y);
}
int subtraction(int x,int y) {
	return (x-y);
}
int multiplication(int x,int y) {
	return (x*y);
}
int division(int x,int y) {
	return (x/y);
}
int main() {
	int a, b, symbol, ret;
	scanf("%d",&a);
	getchar();// Enter会被当做输入字符,丢弃
	symbol = getchar();
	scanf("%d",&b);
	switch(symbol) {
		case '+':
			ret = addition(a, b);
			break;
		case '-':
			ret =subtraction(a,b);
			break;
		default:
			ret = -999;
			break;
	}
	printf("%d%c%d=%d", a,symbol,b,ret);
	return 0;
}

每个函数有一个地址，即该函数第一条指令的地址，
可以用一个指针来保存这个地址，而这个指针就是函数指针。
可以用该指针来调用这个函数。

#include<stdio.h>
int addition(int x,int y) {
	return (x+y);
}
int subtraction(int x,int y) {
	return (x-y);
}
int multiplication(int x,int y) {
	return (x*y);
}
int division(int x,int y) {
	return (x/y);
}
int main() {
	int (*p)(int, int);
	int a, b, symbol, ret;
	scanf("%d",&a);
	getchar();// Enter会被当做输入字符,丢弃
	symbol = getchar();
	scanf("%d",&b);
	switch(symbol) {
		case '+':
			p = addition;
			break;
		case '-':
			p =subtraction;
			break;
		default:
			ret = -999;
			break;
	}
	ret = (*p)(a,b);
	printf("%d%c%d=%d", a,symbol,b,ret);
	return 0;
}

函数指针数组

一组指向函数的指针
例：直接计算100*5

#include<stdio.h>
int addition(int x,int y) {
	return (x+y);
}
int subtraction(int x,int y) {
	return (x-y);
}
int multiplication(int x,int y) {
	return (x*y);
}
int division(int x,int y) {
	return (x/y);
}
int main() {

	int a, b, symbol, ret;
	a = 100;
	b = 5;

	//int (*p)(int, int);
	int (*p[])(int, int) = {addition,subtraction,multiplication,division};

	ret = (*p[2])(a,b);
	printf("%d * %d=%d 
", a,b,ret);

	ret = p[2](a,b);
	printf("%d * %d=%d 
", a,b,ret);
	return 0;
}

运行结果：

100 * 5=500
100 * 5=500