关键字const的扩展

1.定义 
const修饰的数据类型是指常类型，常类型的变量或对象的值是不能被更新的。 
2.限定内容 
例：下面的代码编译器会报一个错误，请问，哪一个语句是错误的呢？

<code class="hljs d has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typedef</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">char</span> * <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> pStr;<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">char</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">string</span>[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>] = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"bbc"</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">char</span> *p1 =<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" string"</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1式</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> pStr p2 =<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">" string"</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//2式</span>p1++;p2++;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

答案与分析： 
问题出在p2++上。 
1）const使用的基本形式： const type m;限定m不可变。替换基本形式中的m为1式中的*p1，替换后const char *p1;限定*p1不可变，当然p1是可变的，因此问题中p1++是对的。替换基本形式中的type为2式中的pStr，替换后const pStr m;限定m不可变，题中的pStr就是一种新类型，因此问题中p2不可[1] 变，p2++是错误的。

3.指针举例 
例一 
下面分别用const限定不可变的内容是什么？ 
1）const在前面

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> nValue； <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//nValue是const</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *pContent; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//*pContent是const, pContent可变</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>* <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> pContent; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//pContent和*pContent都是const</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

2）const在后面，与上面的声明对等

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> nValue; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//nValue是const</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> * pContent; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//*pContent是const, pContent可变</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>* <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> pContent; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//pContent是const,*pContent可变</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span>* <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> pContent; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//pContent和*pContent都是const</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

答案与分析： 
const和指针一起使用是C语言中一个很常见的困惑之处，在实际开发中，特别是在看别人代码的时候，常常会因为这样而不好判断作者的意图，下面讲一下我的判断原则： 
const只修饰其后的变量，至于const放在类型前还是类型后并没有区别。如：const int a和int const a都是修饰a为const。注意*不是一种类型，如果*pType之前是某类型，那么pType是指向该类型的指针 
一个简单的判断方法：指针运算符，是从右到左，那么如：char const pContent，可以理解为char const (* pContent)，即* pContent为const，而pContent则是可变的。

例二

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> * p1,p2;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

p2是const；(p1)是一整体，因此(*p1)是const，但p1是可变的。int p1,p2只代表p1是指向整型的指针，要表示p1、p2都是指针是需写成int * p1,* p2。所以无论是* const p1,p2还是const * p1,p2，里面的*都是属于p1的。

例三

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> * <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> p1,p2;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

p2是const，是前一个const修饰的，*p1也被前一个const修饰，而p1被后一个const修饰。

例四

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> * <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> p1,p2;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

p1是const，（* const p1）是整体，所以const不修饰p2。

例五 
指针指向及其指向变量的值的变化 
const在的左边，则指针指向的变量的值不可直接通过指针改变（可以通过其他途径改变）；在的右边，则指针的指向不可变。简记为“左定值，右定向”。 
1）指针指向的变量的值不能变，指向可变

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> x = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> y = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>* px = &x;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span>* px = &x; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这两句表达式一样效果</span>px = &y; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//正确，允许改变指向</span>*px = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//错误，不允许改变指针指向的变量的值</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

2）指针指向的变量的值可以改变，指向不可变

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> x = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> y = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>* <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> px = &x;px = &y; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//错误，不允许改变指针指向</span>*px = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//正确，允许改变指针指向的变量的值</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

3）指针指向的变量的值不可变，指向不可变

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> x = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> y = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>* <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> px = &x;<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span>* <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> px = &x;px = &y; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//错误，不允许改变指针指向</span>*px = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//错误，不允许改变指针指向的变量的值</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

补充 
在c中，对于const定义的指针，不赋初值编译不报错，

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>* <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> px;  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这种定义是不允许的。（指针常量定义的时候对其进行初始化）</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> *px;  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这种定义是允许的。（常指针可以再定义的时候不初始化）</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

但是，在C++中 
int* const px; //和const int* const px;会报错，const int* px;不报错。 
初始化指针的指向int* const px = &x;const int* const px=&x; 
强烈建议在初始化时说明指针的指向，防止出现野指针！