C:指针函数一些误区

当我们学完指针，知道每个数在内存中都占有一定的字节，也就是地址，才有取地址符号&,所以要交换两个数必须把这两个数所对应的内存互换，比如a=2;b=3;要让它们互换且输出，我们用一个函数来试试

 #include "stdio.h"
 int temp(int x,int y)
 {
     int c;
     c=x;
     x=y;
     y=c;
     }
 void main()
 {
     int a,b;
     a=;
     b=;
     temp(a,b);
     printf("a=%d,b=%d",a,b);
 }

很显然，这个方法并不行，它只是在表面互换a,b的值，并且函数只有在运行的时候是有内存的，当结束时，函数的内存便撤掉，让我们再看一个更让人误解的例子：

 #include "stdio.h"
 int temp(int x,int y)
 {
 int *p,*q,t;
 p=&x;
 q=&y;
 t=*p;
 *p=*q;
 *q=t;
 }
 void main()
 {
    int a,b;
    a=;
    b=;
    temp(a,b);
    printf("a=%d,b=%d",a,b);
 }

上面函数用了指针为什么还是不行？其实跟上一个例子差不多，在主函数main()中调用temp(a,b)作为实参传递给int temp(int x,int y)形参期间传递的是值2,3；并不是a,b的地址,然后取的是2,3的地址，结果就是2,3的地址互换,然而a=2,b=3还是没变，接下来看个正确是例子：

 #include "stdio.h"
 int temp(int *p,int *q)
 {
 int t;
 t=*p;
 *p=*q;
 *q=t;
 }
 void main()
 {
     int a,b;
     a=;
     b=;
     temp(&a,&b);
     printf("a=%d,b=%d",a,b);
 }

运行结果：aaarticlea/png;base64,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" alt="" />,这时实参是temp(&a,&b);互换a,b的地址。