鍍金池/ 教程/ C/ Objective-C 指向指針的指針
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Objective-C 指針運(yùn)算
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Objective-C 指向指針的指針

指針的指針是多個(gè)間接或指針鏈的一種形式。正常情況下,指針包含一個(gè)變量的地址。當(dāng)我們定義了一個(gè)指向指針的指針,第一個(gè)指針包含的地址的第二指針,它指向包含實(shí)際的值的位置,如下圖所示。

Yiibaier to Yiibaier in C

這是一個(gè)指向指針的指針的變量必須在聲明等。這是通過(guò)在它的名字前面放置一個(gè)附加的星號(hào)。例如,以下是聲明一個(gè)指向int類(lèi)型的指針的聲明:

int **var;

當(dāng)一個(gè)目標(biāo)值間接指向由一個(gè)指向指針的指針,訪問(wèn)該數(shù)值,需要星號(hào)運(yùn)算符被應(yīng)用兩次,如下面的例子中所示:

#import <Foundation/Foundation.h>
 
int main ()
{
   int  var;
   int  *ptr;
   int  **pptr;

   var = 3000;

   /* take the address of var */
   ptr = &var;

   /* take the address of ptr using address of operator & */
   pptr = &ptr;

   /* take the value using pptr */
   NSLog(@"Value of var = %d
", var );
   NSLog(@"Value available at *ptr = %d
", *ptr );
   NSLog(@"Value available at **pptr = %d
", **pptr);

   return 0;
}

上面的代碼編譯和執(zhí)行時(shí),它會(huì)產(chǎn)生以下結(jié)果:

2013-09-14 00:41:45.687 demo[22087] Value of var = 3000
2013-09-14 00:41:45.687 demo[22087] Value available at *ptr = 3000
2013-09-14 00:41:45.687 demo[22087] Value available at **pptr = 3000