函数指针学习一

朱雀 2022-08-10 15:55 123阅读 0赞

//函数指针
    
    #include <stdio.h>
    
    int add(int a, int b)
    {
    	return a + b;
    }
    
    int mul(int a, int b)
    {
    	return a * b;
    }
    
    typedef int (*p_t)(int, int);
    //typedef int (*)(int, int) p_t; wrong
    int main(void)
    {
    	int a = 8;
    	int b = 10;
    
    	p_t  p;
    
    	//int (*p)(int, int);　
    	//指向一类函数，参数为(int, int) 返回值为int
    	//函数指针加小括号(*p)
    	p = add;   //指针初始化
    	printf("%d + %d = %d\n", a, b , p(a, b));
    
    	p = mul;
    	printf("%d x %d = %d\n", a, b , p(a, b));
    
    	return 0;
    
    }
    
    
    /*
    akaedu@akaedu-G41MT-D3:~/lin/802$ ./1
    8 + 10 = 18
    8 x 10 = 80
    akaedu@akaedu-G41MT-D3:~/lin/802$ 
    */
    
    <pre name="code" class="cpp">
    
    
    
    
    
    
    
    
    
    
    //回调函数
    #include <stdio.h>
    
    typedef int (*p_t)(int, int);
    
    int add(int a, int b)
    {
    	return a + b;
    }
    
    void func(p_t p, int a, int b)
    {
    	printf("%d + %d = %d\n", a, b, p(a, b));
    }
    int main(void)
    {
    	p_t p;
    	p = add;
    
    	func(p, 3, 8);
    	return 0;
    }<pre name="code" class="cpp">
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    //变参函数
    #include <stdio.h>
    #include <stdarg.h>
    
    void print(int last, ...)
    {
    	va_list ap;		// typedef char * va_list
    	char *p;
    	va_start(ap, last); //找出第一个指针的地址保存到ap指针里面
    						// ap = &last + sizeof(last)
    	p = va_arg(ap, char *); // 取出当前指针的内容
    							//va_arg(ap, type);
    							// *((type)(ap += sizeof(type) - sizeof(type)))
    	while(p != NULL){
    		printf("%s", p);
    		p = va_arg(ap, char *);
    	}
    
    	printf("\n");
    	
    	va_end(ap);	//类似于malloc的free
    			    //#define ap NULL
    }
    
    
    int main(void)
    {
    
    	print(100, "hehe", "haha", "xixi", NULL);
    	print(10, "hehe", "hello", "akak", NULL);
    	print(1, "hehe",  NULL);
    	return 0;
    
    }

</pre><pre code_snippet_id="441585" snippet_file_name="blog_20140803_4_1439010" name="code" class="cpp">

</pre><pre code_snippet_id="441585" snippet_file_name="blog_20140803_5_2862542" name="code" class="cpp"><pre name="code" class="cpp">#include <stdio.h>
    #include <stdarg.h>
    
    void print_int(int num, ...)
    {
    	int i;
    //	n = num;
    	va_list ap;
    	va_start(ap, num);
    
    //	p = va_arg(ap, num);
    	
    	while(num > 0){
    		i = va_arg(ap, int);
    		printf("%d ", i);
    		num--;
    	}
    
    	va_end(ap);
    
    }
    
    
    int main(void)
    {
    
    	print_int(5, 1, 2, 3, 4, 5);
    	putchar('\n');
    
    	print_int(8, 88, 2, 3, 4, 5, 88, 66, 8 );
    	putchar('\n');
    	return 0;
    
    }
    
    /*
    akaedu@akaedu-G41MT-D3:~/lin/802$ ./6
    1 2 3 4 5 
    88 2 3 4 5 88 66 8 */<pre name="code" class="cpp">
    
    
    
    
    
    //my_printf
    
    
    #include <stdio.h>
    #include <stdarg.h>
    
    void myprintf(const char *format, ...)
    {
    
    	va_list ap;
    	char c;
    
    	va_start(ap, format);
    	while((c = *format++)){
    		switch(c){
    
    			case 'c':{
    				char ch = va_arg(ap, int);
    			//	char ch = va_arg(ap, char);
    				putchar(ch);
    				break;
    			}
    			case 's':{
    				char *p = va_arg(ap, char *);
    				fputs(p, stdout);
    				break;
    			}
    			case 'd':{
    				int p = va_arg(ap, int);
    				int i = p + '0';
    				putchar(i);
    				break;
    			}
    		//	case 'p':{
    		
    		//	}
    
    			default:
    				putchar(c);
    		}
    	}
    
    	va_end(ap);
    }
    
    int main(void)
    {
    	myprintf("c\ts\td\n", 'm', "hello", 8);
    	return 0;
    
    }
    
    /*
    akaedu@akaedu-G41MT-D3:~/lin/802$ ./8
    m	hello	8
    akaedu@akaedu-G41MT-D3:~/lin/802$ 
    */