blocks|key|3418284|text|根据你的评论：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3418285|3418286|我刚刚检查过了，调用函数只是把它当作一个有效的双精度值来使用(在if语句中)|blockquote|3418287|3418288|3418289|我只需将函数修改为return+0;，而不是return+NULL;|offset|length|style|CODE|3418290|entityMap^0|0|0|0|0|0|9|9|M|C|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|R|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|T|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|U|8|@$J|V|K|W|L|M]|$J|X|K|Y|L|M]]|9|@]|A|$]]|$1|N|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|O|$]]

Based on your comment:

<blockquote>
 I just checked, and the calling functions just use it as if it is a valid double (in an if statement) 
</blockquote>

I would just modify the function to <code>return 0;</code> instead of <code>return NULL;</code>

blocks|key|2010662|text|通过编译器选项，可能有一个"NaN“(而不是一个数字)功能。但这仍然不会是null。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2010663|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|$]]

There might be a "NaN" (not a number) capability, via compiler options. But that still won't be a null.

blocks|key|2010696|text|这不是一个编译器选项，但您可以(在理论上)使用#define+NULL+0来获得所需的效果。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2010697|entityMap^0|N|E|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

It's not a compiler option, but you could <code>#define NULL 0</code> to (in theory) get the desired effect.

blocks|key|524291|text|你确定他们不会返回指向双精度的指针吗？NULL+double没有意义，因为零是double的有效值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|524292|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|$]]

Are you sure they don't return pointer-to-double? A NULL double is meaningless, since zero is a valid value for double.

blocks|key|1271567|text|当NULL从函数返回时，它不一定有特殊的含义。如果你想指出一个函数没有成功完成，常用的技术是返回一些在正常情况下永远不会返回的值。通常，这意味着返回一个无效值。当函数返回指针时，它通常使用NULL作为返回值，表示出现错误，因为NULL指针很少是用户期望函数返回的值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1271568|常量NULL只在指针上下文中有意义，而且由于您返回的是标量值，编译器会抱怨您使用NULL。不返回NULL，而是找到一些永远不会是有效返回值的值，并将其用作错误指示器。为了更清楚地说明您在做什么，请使用#define+AN_ERROR_OCCURED+<<someval>>将该值作为常量的别名，以避免使用“魔术数字”。|1271569|另一种常见的方法是使用全局errno+(see+errno.h)。如果您的函数遇到错误，请在返回前将errno设置为某个非零值。然后，调用您的函数的代码将可以使用诸如if+(errno)+{...}之类的东西来检查和处理错误。|1271570|另一种方法是，如果函数成功，则返回零，否则返回非零错误代码。如果用户需要从函数获取数据，则必须将额外的“返回缓冲区”指针传递给函数。|1271571|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Errno.h^0|1|4|2M|4|35|4|0|2|4|14|4|1C|4|2S|10|0|D|5|1E|5|2B|G|K|B|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|19|8|@$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@$9|1G|A|1H|1|1I]]|E|$]]|$1|J|3|K|5|6|7|1J|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

<code>NULL</code> doesn't necessarily have a special meaning when it is returned from a function. If you want to indicate that a function did not complete successfully, the common technique is to return some value that would never be returned under normal circumstances. Usually, this means returning an invalid value. When a function returns a pointer, it often uses <code>NULL</code> as a return value signaling an error since a <code>NULL</code> pointer is rarely a value that the user would expect the function to return.

The constant <code>NULL</code> only has meaning in the context of pointers, and since you are returning a scalar value the compiler is griping at you about using <code>NULL</code>. Instead of returning <code>NULL</code>, find some value that could never be a valid return value and use it as your error indicator. To make it more clear what you are doing, alias that value with a constant using <code>#define AN_ERROR_OCCURED &lt;&lt;someval&gt;&gt;</code> to avoid using "magic numbers".

Another common way to do it is to use the <code>errno</code> global (<a href="http://en.wikipedia.org/wiki/Errno.h" rel="nofollow noreferrer">see errno.h</a>). If your function encounters an error, set <code>errno</code> to some non-zero value before returning. The code calling your function will then can check for and handle errors using something like <code>if (errno) {...}</code>.

Yet another method is to have the function return zero if successful and a non-zero error code otherwise. If the user needs to get data back from the function, an extra "return buffer" pointer would have to be passed to the function.

blocks|key|1271592|text|我想我将使用#ifdef+INTEL作为编译器标志，并将该编译时选项的返回值定义为零。有点痛苦，但似乎是最好的方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1271593|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|$]]

I think I will just use #ifdef INTEL for a compiler flag, and define the return as zero for that compile time option. Kind of a pain, but seems to be the best way.

I have some code that I am porting from an SGI system using the MIPS compiler. It has functions that are declared to have double return type. If the function can't find the right double, those functions return "NULL"

The intel C compiler does not like this, but I was trying to see if there is a compiler option to enable this "feature" so that I can compile without changing code. I checked the man page, and can't seem to find it.

Thanks

Example of the code that currently exists, and works fine with MIPS

<pre><code> double some_function(int param){
 double test = 26.25;
 if(param == 10){
 return test;
 }
 return (NULL);
 }
</code></pre>

the intel compiler complains:
error: return value type does not match the function type

how to return NULL for double function with Intel C compiler?

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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我有一些使用MIPS编译器从SGI系统移植过来的代码。它具有声明为具有双返回类型的函数。如果函数找不到正确的双精度值，这些函数将返回"NULL“英特尔C编译器不喜欢这样，但我想看看是否有一个编译器选项来启用这个“功能”，这样我就可以在不更改代码的情况下进行编译。我查看了手册页，似乎找不到它。谢谢当前存在的代码示例，可以很好地使用MIPS double some_function(int param

问如何在英特尔C编译器中为双精度函数返回NULL？
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