值傳遞與地址傳遞

 

 

 

對於是值傳遞還是地址傳遞不能通過行參來判斷，當形參是指針時既有可能是值傳遞也有可能是地址傳遞，要畫圖分析，幾個例子如下

 

void Exchg1(int x, int y)
{
  int tmp;
  tmp=x;
  x=y;
  y=tmp;

}
void main()
{
  int a=4,b=6;
  Exchg1 (a,b) ;
  printf("a=%d,b=%d\n",a,b);//4,6
}

void Exchg2(int *px, int *py)
{
  int tmp=*px;
  *px=*py;
   *py=tmp;

}
void main()
{
  int a=4;
  int b=6;
      Exchg2(&a,&b);
      printf("a=%d,b=%d\n", a, b);//6,4
}

 

void Exchg2(int &x, int &y)
{
   int tmp=x;
   x=y;
   y=tmp;

}
void main()
{
  int a=4;
  int b=6;
      Exchg2(a,b);
      printf("a=%d,b=%d\n", a, b);//6,4
}

 

 

 

void swap(int *a,int *b)
{
        int *tmp=NULL;
        tmp=a;
        a=b;
        b=tmp;
}

int main(int argc,char **argv)
{
        int a=2;
        int b=3;
        printf("Before swap a=%d  b=%d\n",a,b);
        swap(&a,&b);
        printf("After swap a=%d  b=%d\n",a,b); //2,3
        return 0;
}

 

void swap(int **a,int **b)
{
int temp = **a;
**a = **b;
**b = temp;
}

int main()
{
int i = 1;
int j = 2;

int *p1 = &i;
int *p2 = &j;

int *a = p1;
int *b = p2;

swap(&a,&b);
printf("a = %d,b = %d\n",i,j);//2,1
return 0;
}