blocks|key|3998844|text|如果返回值是一个指针，那么在发生错误的情况下，NULL是最符合逻辑的值。你也可以考虑引发一个异常，但是现在返回NULL应该能满足你的需要。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3998845|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If your return value is a pointer then NULL is the most logical value in the case of an error. You could also look at raising an exception, but for now returning NULL should suit your needs.

blocks|key|2363821|text|operator+new抛出异常(nothrow+operator+new除外)，所以你可以捕捉这个异常并返回null+pointer，或者重新抛出，或者抛出其他异常。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2363822|entityMap^0|0|C|H|K|1J|C|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

<code>operator new</code> throws exception (except <code>nothrow operator new</code>), so, you can catch this exception and return <code>null pointer</code>, or rethrow, or throw other exception.

blocks|key|2236731|text|在函数分配自己的内存并返回指向它的指针的分配失败的情况下，返回NULL是一种习惯。有关示例strdup()，请参阅。请注意，如果运算符new无法分配内存，则它会抛出std::bad_alloc，因此如果您希望返回NULL，则可能需要捕获此异常，或者，您可以让std::bad_alloc传播到函数之外。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2236732|但是，请注意，返回此类指针并不总是明智的，因为它会引发所有权问题，并增加内存泄漏的可能性。|2236733|您可能会发现，坚持使用RAII习惯用法可以使您的代码更容易理解，也更不容易出错。RAII惯用法的一个结果是，分配和释放由相同的代码单元完成。|2236734|在您的特定情况下，您可以在main()中分配数组，因此您可以将指向它的指针传递给foo()，也可以在main()中释放内存。|2236735|此外，如果您使用new进行分配，则应该使用适当版本的delete来解除分配(这里是delete[]，因为您分配了一个数组)。您可以使用free()释放分配给malloc()和朋友的内存。|2236736|entityMap|0|LINK|mutability|MUTABLE|url|http://linux.die.net/man/3/strdup|1|http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization^0|19|8|1V|3|2A|E|3L|E|19|8|0|0|0|B|4|1|0|D|6|14|5|1E|6|0|8|3|Q|6|15|8|1V|6|26|8|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@$9|16|A|17|1|18]]|E|$]]|$1|F|3|G|5|6|7|19|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1A|8|@]|D|@$9|1B|A|1C|1|1D]]|E|$]]|$1|J|3|K|5|6|7|1E|8|@$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]]|D|@]|E|$]]|$1|L|3|M|5|6|7|1L|8|@$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]|$9|1Q|A|1R|B|C]|$9|1S|A|1T|B|C]|$9|1U|A|1V|B|C]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|1W|8|@]|D|@]|E|$]]]|O|$P|$5|Q|R|S|E|$T|U]]|V|$5|Q|R|S|E|$T|W]]]]

It is a custom to return NULL in case of allocation failure from functions which allocate their own memory and return pointer to it. See for example <a href="http://linux.die.net/man/3/strdup" rel="nofollow"><code>strdup()</code></a>. Note that operator <code>new</code> throws <code>std::bad_alloc</code> if it fails to allocate memory, so you may need to catch this if you want to return NULL or alternatively, you can let <code>std::bad_alloc</code> propagate out of the function. 

Note however, that it is not always wise to return such pointers since it raises the issues of ownership and increases the likelihood of memory leaks.

You may find that sticking to the <a href="http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization" rel="nofollow">RAII</a> idiom makes your code easier to reason about and less error prone. One consequence of RAII idiom is that allocation and deallocation are done by the same code unit.

In your particular situation you allocate the array in <code>main()</code> so you may pass the pointer to it to <code>foo()</code> and deallocate memory also in <code>main()</code>.

Also, if you use <code>new</code> to allocate, you should use a proper version of <code>delete</code> to deallocate (here <code>delete[]</code> since you allocated an array). You use <code>free()</code> to deallocate memory allocated with <code>malloc()</code> and friends.

blocks|key|4090235|text|在这种情况下，新运算符将抛出bad_alloc异常，您可能应该捕获它并根据您的要求处理它(http://www.cplusplus.com/reference/std/new/bad_alloc/)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4090236|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cplusplus.com/reference/std/new/bad_alloc/^0|19|1H|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

The new operator would throw a bad_alloc exception in such a case and probably you should catch it and handle it according to your requirements (<a href="http://www.cplusplus.com/reference/std/new/bad_alloc/" rel="nofollow">http://www.cplusplus.com/reference/std/new/bad_alloc/</a>)

blocks|key|2363901|text|它可以返回任何值。问题是，你必须正确对待它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2363902|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It can return any value. The thing is that then you have to treat it correctly.

blocks|key|4090277|text|if(!a)+//+what+should+I+return+here+if+allocation+of+a+fails+

+{+return+NULL;}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4090278|这将意味着分配失败，即返回空指针。|unstyled|4090279|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>if(!a) // what should I return here if allocation of a fails 

 { return NULL;}
</code></pre>

this will imply allocation failed i.e. by returning a NULL pointer.

blocks|key|3999026|text|如果分配失败，new运算符会抛出bad_alloc异常。因此，您可以捕获此异常并处理错误。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3999027|例如：|3999028|#include+<new>+//+std::bad_alloc

int*+foo(int+n)
{
+++int*+a(new+int[n]);

+++return+a;+//+I+guess+you+want+to+return+the+address+stored+in+a
}

int+main()
{
+++try
+++{
++++++int*+a(foo(n));
+++}
+++catch(std::bad_alloc&+ba)
+++{
++++++//+Handle+here+the+error+(e.g:+std::cerr+<<+"Allocation+failed:"+<<+ba.what()+<<+std::endl;)
+++}

+++return+0;
}|code-block|syntax|javascript|3999029|EDIT1:如果您使用C%2B%2B11特性，请忘记NULL或0，转而使用nullptr！|BOLD|3999030|entityMap^0|7|3|G|9|0|0|0|0|6|M|4|R|1|X|7|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|X|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|Y|8|@$9|Z|A|10|B|O]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|P|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|Q|$]]

The <code>new</code>operator throws a <code>bad_alloc</code> exception if allocation fails. So you can catch this exception and handle the error.

For exemple:

<pre><code>#include &lt;new&gt; // std::bad_alloc

int* foo(int n)
{
 int* a(new int[n]);

 return a; // I guess you want to return the address stored in a
}

int main()
{
 try
 {
 int* a(foo(n));
 }
 catch(std::bad_alloc&amp; ba)
 {
 // Handle here the error (e.g: std::cerr &lt;&lt; "Allocation failed:" &lt;&lt; ba.what() &lt;&lt; std::endl;)
 }

 return 0;
}
</code></pre>

EDIT1: If you use C++11 features, forget <code>NULL</code> or <code>0</code> and use <code>nullptr</code> instead!

<pre><code>int main()
{

 cout&lt;&lt;"Enter n";

 cin &gt;&gt; n;

 int * a = new int[n];

 a = foo(n);

 free(a);

 return -1;

}

int * foo(int n)
{
 int * a = new int [n];

 if(!a) // what should I return here if allocation of a fails 

 {}

 free(a);


} 
</code></pre>

In the code above I am trying to catch the return value of an function from main, the return type of the function is a pointer . However I am allocating memory dynamically . So , what should I return if my memory allocation fails ... any special symbol like NULL . 

P.S - Its a very basic question and could not formalize my question to any succinct form for to search over Google.

Edit: Thanks all of you guys . I have solved my problem .

Function return value when fail to allocate space

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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int main(){ cout<<"Enter n"; cin >> n; int * a = new int[n]; a = foo(n); free(a); return -1;}int * foo(int n){ int * a = new int [n]; if(!a) // what should I re...

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