随机过程

http://superware.blog.163.com

日志

关于我

superware

茕茕孑立,踽踽独行。

文章分类

LOFTER精选

八招诀窍，教你实力撩妹 >

网易考拉推荐

变量、指针、引用与形参初始化

2014-07-07 19:56:39| 分类：默认分类 | 标签： |举报 |字号大中小订阅

下载LOFTER 我的照片书 |

        C++ 关于函数参数是这样规定的：按照形参初始化方式，函数参数有两种：拷贝初始化方式和直接初始化方式。

拷贝初始化：形参初始化是通过拷贝实参来实现；
直接初始化：形参初始化是通过直接赋予变量地址的方式来实现。

        有个认识：对变量的访问都是通过地址访问的，在汇编语言中，变量存储与内存中，变量占据内存块，并有一个首地址。对变量的访问必须首先确定首地址。首地址的确定方式有两种：直接访问和间接访问。直接访问是通过变量地址访问，间接访问是通过内存中所存储的另一个变量的地址进行间接访问。

一、拷贝初始化形参

        拷贝初始化形参有两种：直接形参和指针形参。

1、直接形参如下：

void swap_cpy (int a, int b)
{
  ...
}

直接形参是将实参的值拷贝给形参，对形参的访问与实参没任何关系。

2、指针形参如下：

void swap_ptr (int *a, int *b)
{
  ...
}

指针形参方式是：将实参的地址拷贝给指针变量，而指针的地址才是直接访问指针变量的地址。

二、非拷贝初始化形参

直接初始化形参方式就是引用：

void swap_ref (int &a, int &b)
{
  ...
}

引用就是将实参的地址直接给形参，形参地址就是实参地址。

三、举例说明

#include <iostream>

using namespace std;

void swap_cpy (int a, int b)
{
  int c;

  c = a;
  a = b;
  b = c;

  cout << "--- swap_cpy (int a, int b) begins ---" << endl;
  cout << "a = " << a << ", " << "b = " << b << endl;
  cout << "&a = " << &a << ", " << "&b = " << &b << endl;
  cout << "--- swap_cpy (int a, int b) ends --- " << endl;
}

void swap_ptr (int *a, int *b)
{
  int c;

  c = *a;
  *a = *b;
  *b = c;

  cout << "--- swap_cpy (int *a, int *b) begins ---" << endl;
  cout << "*a = " << *a << ", " << "*b = " << *b << endl;
  cout << "a = " << a << ", " << "b = " << b << endl;
  cout << "&a = " << &a << ", " << "&b = " << &b << endl;
  cout << "--- swap_cpy (int *a, int *b) ends ---" << endl;
}

void swap_ref (int &a, int &b)
{
  int c;

  c = a;
  a = b;
  b = c;

  cout << "--- swap_cpy (int &a, int &b) begins ---" << endl;
  cout << "a = " << a << ", " << "b = " << b << endl;
  cout << "&a = " << &a << ", " << "&b = " << &b << endl;
  cout << "--- swap_cpy (int &a, int &b) ends ---" << endl;
}

void try_ref ()
{
  int x = 1;
  int y = 8;

  cout << "x = " << x << ", " << "y = " << y << endl;
  cout << "&x = " << &x << ", " << "&y = " << &y << endl;
  cout << endl;

  cout << "*** before swap_cpy (int x, int y) *** " << endl;
  cout << "x = " << x << ", " << "y = " << y << endl;
  swap_cpy (x, y);
  cout << "*** after swap_cpy (int x, int y) ***" << endl;
  cout << "x = " << x << ", " << "y = " << y << endl;
  cout << endl;

  cout << "*** before swap_ptr (int *x, int *y) ***" << endl;
  cout << "x = " << x << ", " << "y = " << y << endl;
  swap_ptr (&x, &y);
  cout << "*** after swap_cpy (int *x, int *y) ***" << endl;
  cout << "x = " << x << ", " << "y = " << y << endl;
  cout << endl;

  cout << "*** before swap_ptr (int &x, int &y) ***" << endl;
  cout << "x = " << x << ", " << "y = " << y << endl;
  swap_ref (x, y);
  cout << "*** after swap_cpy (int &x, int &y) ***" << endl;
  cout << "x = " << x << ", " << "y = " << y << endl;
  cout << endl;
}

int main ()
{
  try_ref ();

  return 0;
}

结果：

x = 1, y = 8
&x = 0x7fffee33dfac, &y = 0x7fffee33dfa8  // 实参地址

*** before swap_cpy (int x, int y) *** 
x = 1, y = 8
--- swap_cpy (int a, int b) begins ---
a = 8, b = 1
&a = 0x7fffee33defc, &b = 0x7fffee33def8  // 形参地址，不同于实参地址
--- swap_cpy (int a, int b) ends --- 
*** after swap_cpy (int x, int y) ***
x = 1, y = 8

*** before swap_ptr (int *x, int *y) ***  
x = 1, y = 8
--- swap_cpy (int *a, int *b) begins ---
*a = 8, *b = 1
a = 0x7fffee33dfac, b = 0x7fffee33dfa8     // 指针变量的值，是实参地址
&a = 0x7fffee33def8, &b = 0x7fffee33def0   // 指针变量地址
--- swap_cpy (int *a, int *b) ends ---
*** after swap_cpy (int *x, int *y) ***
x = 8, y = 1

*** before swap_ptr (int &x, int &y) ***
x = 8, y = 1
--- swap_cpy (int &a, int &b) begins ---  
a = 1, b = 8
&a = 0x7fffee33dfac, &b = 0x7fffee33dfa8   // 引用就是实参地址
--- swap_cpy (int &a, int &b) ends ---
*** after swap_cpy (int &x, int &y) ***
x = 1, y = 8

评论这张

转发至微博

阅读(48)| 评论(0)

历史上的今天

this.p={  m:2,
              b:2,
              loftPermalink:'',
              id:'fks_087071082095087067093085082070072087081075093081087070093080',
              blogTitle:'变量、指针、引用与形参初始化',
              blogAbstract:'<br\><font size=\"2\"   \>        C++ 关于函数参数是这样规定的：按照形参初始化方式，函数参数有两种：拷贝初始化方式和直接初始化方式。<br\><br\>拷贝初始化：形参初始化是通过拷贝实参来实现；<br\>直接初始化：形参初始化是通过直接赋予变量地址的方式来实现。</font\><br\><br\><i\><font size=\"2\"   \>        有个认识：对变量的访问都是通过地址访问的，在汇编语言中，变量存储与内存中，变量占据内存块，并有一个首地址。对变量的访问必须首先确定首地址。首地址的确定方式有两种：直接访问和间接访问。直接访问是通过变量地址访问，间接访问是通过内存中所存储的另一个变量的地址进行间接访问。</font\></i\>',
              blogTag:'',
              blogUrl:'blog/static/10897159620146773558208',
              isPublished:1,
              istop:false,
              type:2,
              modifyTime:1404734577167,
              publishTime:1404734199592,
              permalink:'blog/static/10897159620146773558208',
              commentCount:0,
              mainCommentCount:0,
              recommendCount:0,
              bsrk:-100,
              publisherId:0,
              recomBlogHome:false,
              currentRecomBlog:false,
              attachmentsFileIds:[],
              vote:{},
              groupInfo:{},
              friendstatus:'none',
              followstatus:'unFollow',
              pubSucc:'',
              visitorProvince:'',
              visitorCity:'',
              visitorNewUser:false,
              postAddInfo:{},
              mset:'000',
              mcon:'',
              srk:-100,
              remindgoodnightblog:false,
              isBlackVisitor:false,
              isShowYodaoAd:false,
              hostIntro:'茕茕孑立,踽踽独行。',
              hmcon:'1',
              selfRecomBlogCount:'0',
              lofter_single:'<iframe width="140" height="560" style="overflow:hidden;" src="http://www.lofter.com/mailEntry.do?blogad=1&blog" frameBorder="0"></iframe>'
            }

{list a as x}
    {if !!x}
    <div class="iblock nbw-fce nbw-f40">
      <a class="fc03 noul" target="_blank" hidefocus="true" href="http://blog.163.com/${x.visitorName}/">
      {if x.visitorName==visitor.userName}
      <img alt="${x.visitorNickname|escape}" onerror="this.src=location.f40" class="cwd bdwa bdc0" src="${fn1(x.visitorName)}&r=${visitor.imageUpdateTime}"/>
      {else}
      <img alt="${x.visitorNickname|escape}" onerror="this.src=location.f40" class="cwd bdwa bdc0" src="${fn1(x.visitorName)}"/>
      {/if}
      </a>
      <div class="cwd vname thide">
        {if x.moveFrom=='wap'}
          <a class="noul pnt" target="_blank" href="http://blog.163.com/services/wapblog.html?frompersonalbloghome"><span title="来自网易手机博客" class="iblock wapIcon"> </span></a>
        {elseif x.moveFrom=='iphone'}
          <a class="noul pnt" target="_blank"><span title="来自iPhone客户端" class="iblock iphoneIcon"> </span></a>
        {elseif x.moveFrom=='android'}
          <a class="noul pnt" target="_blank"><span title="来自Android客户端" class="iblock androidIcon"> </span></a>
        {elseif x.moveFrom=='mobile'}
          <a class="noul pnt" target="_blank" href="http://blog.163.com/services/emsblog.html?frompersonalbloghome"><span title="来自网易短信写博" class="iblock wapIcon"> </span></a>
        {/if}
        <a class="fc03 m2a"  target="_blank" hidefocus="true" href="http://blog.163.com/${x.visitorName}/">
          ${fn(x.visitorNickname,8)|escape}
        </a>
      </div>
    </div>
    {/if}
    {/list}

<#--最新日志，群博日志--> <#--推荐日志-->

<p class="fc06">推荐过这篇日志的人：</p>
    <div>
      {list a as x}
      {if !!x}
      <div class="iblock nbw-fce nbw-f40">
        <a class="fc03 noul" target="_blank" hidefocus="true" href="http://blog.163.com/${x.recommenderName}/">
        <img alt="${x.recommenderNickname|escape}" onerror="this.src=location.f40" class="cwd bdwa bdc0" src="${fn1(x.recommenderName)}"/>
        </a>
        <div class="cwd thide">
          <a class="fc03 m2a" target="_blank" hidefocus="true" href="http://blog.163.com/${x.recommenderName}/">
            ${fn(x.recommenderNickname,6)|escape}
          </a>
        </div>
      </div>
      {/if}
      {/list}
    </div>
    {if !!b&&b.length>0}
    <p  class="fc06">他们还推荐了：</p>
    <ul>
    {list b as y}
      {if !!y}
        <li class="rrb"><span class="iblock">·</span><a class="fc03 m2a" target="_blank" href="http://blog.163.com/${y.recommendBlogPermalink}/?from=blog/static/10897159620146773558208">${y.recommendBlogTitle|escape}</a></li>
      {/if}
    {/list}
    </ul>
    {/if}

<#--引用记录--> <#--博主推荐--> <#--随机阅读--> <#--首页推荐--> <#--历史上的今天--> <#--被推荐日志--> <#--上一篇，下一篇--> <#-- 热度 -->

{list a as x}
    {if !!x}
    <div class="hotItem iblock nbw-fce nbw-f40">
      <a class="fc03 noul" target="_blank" hidefocus="true" href="http://blog.163.com/${x.publisherUsername}/">
      {if x.publisherUsername==visitor.userName}
      <img alt="${x.publisherNickname|escape}" onerror="this.src=location.f40" class="cwd bdwa bdc0" src="${fn1(x.publisherUsername)}&r=${visitor.imageUpdateTime}"/>
      {else}
      <img alt="${x.publisherNickname|escape}" onerror="this.src=location.f40" class="cwd bdwa bdc0" src="${fn1(x.publisherUsername)}"/>
      {/if}
      </a>
      <div class="cwd vname thide">
        <a class="fc03 m2a"  target="_blank" hidefocus="true" href="http://blog.163.com/${x.publisherUsername}/">
          ${fn(x.publisherNickname,8)|escape}
        </a>
      </div>
      <a class="f-myLikeIcons hottype {if x.type==1} js-liketype{elseif x.type==2} js-reblogtype{elseif x.type==3} js-sharetype{else}{/if}" target="_blank" hidefocus="true" href="http://blog.163.com/${x.publisherUsername}/"> </a>
    </div>
    {/if}
    {/list}

<#-- 网易新闻广告 --> <#--右边模块结构--> <#--评论模块结构--> <#--引用模块结构--> <#--博主发起的投票-->

页脚

我的照片书 - 博客风格 - 手机博客 - 下载LOFTER APP - 订阅此博客

随机过程

导航

日志

变量、指针、引用与形参初始化

历史上的今天

最近读者

热度

评论

页脚