blocks|key|3168618|text|如果你真的想要一种多线程、可重入的方式来报告错误，我认为你不能在每次lib调用中都传递一个指向"status“结构的指针。除了其他对象状态内容之外，该结构还会包含有问题的调用结果。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3168619|它确实很难看，但不一定不好。|3168620|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

If you really want a multithreaded, reentrant, way to report errors, I think you cannot escape, in every lib call, to pass a pointer to a "status" struct . That struct would have among other object state stuff, the result of the call in question.

It's ugly indeed, but not necessarily bad.

blocks|key|262734|text|将"status“参数作为指针传递可能看起来有点丑陋，但在C编程中是可以接受的，因为高级错误报告工具在C语言中不存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262735|状态变量中的每一位都代表不同的错误，因此如果返回NULL，调用者将必须测试是status+&+ERR_NOMEM还是status+&+ERR_IO等。错误掩码可以定义如下：|offset|length|style|CODE|262736|#define+ERR_NOMEM+(1+<<+0)
#define+ERR_IO++++(1+<<+1)
...|code-block|syntax|javascript|262737|在函数内部设置适当的错误可以作为status+%7C=+ERR_IO来完成。|262738|这甚至使您可以灵活地有时指示多个错误-调用者可以检查status+&+(ERR_NOMEM+%7C+ERR_IO)以测试是否发生了任何错误。|262739|entityMap^0|0|O|4|12|I|1M|F|0|0|G|G|0|Q|T|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@$D|U|E|V|F|G]|$D|W|E|X|F|G]|$D|Y|E|Z|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|11|8|@$D|12|E|13|F|G]]|9|@]|A|$]]|$1|O|3|P|5|6|7|14|8|@$D|15|E|16|F|G]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$]]

Having a "status" argument passed as a pointer may seem a bit ugly, but is accepted in C programming since higher-level error reporting facilities do not exist in the language.

Each bit in the status variable would represent a different error, so if <code>NULL</code> is returned, the caller will have to test whether <code>status &amp; ERR_NOMEM</code> or <code>status &amp; ERR_IO</code>, etc. The error masks can be defined as follows:

<pre><code>#define ERR_NOMEM (1 &lt;&lt; 0)
#define ERR_IO (1 &lt;&lt; 1)
...
</code></pre>

Setting the appropriate error inside the functions could be done as <code>status |= ERR_IO</code>.

This even gives you the flexibility to indicate more than one error sometimes - the caller can check <code>status &amp; (ERR_NOMEM | ERR_IO)</code> to test whether any of the errors have occurred.

blocks|key|262751|text|我有几个建议。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|262752|建议#1+--使用自定义的errnos。我知道您表示不愿使用它。我知道您担心errno会在多线程环境中受到破坏，但我希望每个线程都有自己的errno存储空间。下面的链接http://compute.cnr.berkeley.edu/cgi-bin/man-cgi?errno%2B3表明这很容易做到。|offset|length|style|BOLD|262753|至于定制errno的结构，您总是可以将errno分成两部分……模块号和模块错误代码。|262754|eg.
#define+MODULE_NAME_error_code+((MODULE_NUMBER+<<+16)+%7C+(error_code))|code-block|syntax|javascript|262755|如果在库中检测到错误，则可以将errno设置为所需的值。如果有多个模块，它可以帮助识别问题区域。当然，如果您的库要与使用此方法的其他库一起使用，则需要对自定义errno进行某种形式的同步。|262756|建议#2+--让您的例程在成功时返回0，并在返回时返回一个自定义的非零值，并让其中一个参数成为您想要设置的值的指针。可以很容易地检测到错误；但是，如果您有使用这种方法的深层调用树，则记录这些错误可能会很麻烦。|262757|希望这能有所帮助。|262758|entityMap|0|LINK|mutability|MUTABLE|url|http://compute.cnr.berkeley.edu/cgi-bin/man-cgi?errno%2B3^0|0|0|4|2C|1J|0|0|0|0|0|0|4|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@$D|14|E|15|F|G]]|9|@$D|16|E|17|1|18]]|A|$]]|$1|H|3|I|5|6|7|19|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|1A|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|1B|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1C|8|@$D|1D|E|1E|F|G]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1F|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]]]

I have a couple of suggestions.

Suggestion #1 -- Use custom errnos.
I know that you indicated that you would prefer not to use that. I gather that you are concerned that errno will be clobbered in a multi-threaded environment, but I would expect that each thread should have its own storage for errno. The following link <a href="http://compute.cnr.berkeley.edu/cgi-bin/man-cgi?errno+3">http://compute.cnr.berkeley.edu/cgi-bin/man-cgi?errno+3</a> suggests that it is rather easy to do.

As far as structuring the custom errno's, you can always divide the errno up into two portions ... a module number and an module error code.

<pre><code>eg.
#define MODULE_NAME_error_code ((MODULE_NUMBER &lt;&lt; 16) | (error_code))
</code></pre>

In case of detected errors in your library, you can then set the errno to a desired value. If there are multiple modules, it can help identify the problem area. Of course, if your library is to be used with others that use this method, then some form of synchronization of custom errno's is required.

Suggestion #2 -- Let your routines return 0 on success with a custom non-zero value on return and let one of the parameters be a pointer to the value you want to set. Errors can be detected easily; however documenting them may be troublesome if you have deep call trees that use this methodology.

Hope this helps.

blocks|key|264505|text|我的第一个想法是:为什么不使用stderr，用指示问题来源和原因的消息填充它？或者，可能我没有注意到您的意图:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|264506|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|$]]

My first thought: why not use stderr, filling it with messages indicating source and cause of the problem? Or, maybe I missed your intention :)

blocks|key|260495|text|int+get_data(void+**ptr)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|260496|如果没有明显的“错误返回”，那么也许你的输出值不应该是返回值。错误可以是errno、其他自定义的详细错误值(*cough*+HRESULT)、函数成功与否的true/false或其他一些有用的信息(数据长度，如果出错，则为-1+)|unstyled|260497|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>int get_data(void **ptr)
</code></pre>

If there are no obvious 'error returns', then maybe your output value should not be the return value. The error could either be an errno, some other custom detailed error value (*cough* HRESULT), just true/false for if the function succeeded, or some other bit of useful information (the length of the data, or -1 if error)

I am looking for a robust way to report errors in a C library. Consider the simple example of a queue:

<pre><code>struct queue *q = malloc(sizeof(*q));
if (NULL == q) {
 /* malloc failed. now what ? */
 return NULL; /* maybe ? */
}
</code></pre>

Okay, so for that example returning <code>NULL</code> isn't otherwise valid so it makes sense to return it to signal an error. But

<pre><code>void *get_data()
{
 /* stuff */

 /* Error detected. NULL is a valid return, now what ? */

 /* stuff */
}
</code></pre>

What's more, once we signal an error, how to signal what is the error ? I have thought about it and don't have a satisfying solution.

<ul>
<li>Using <code>errno</code> or some other global object isn't
something I would like to do (perhaps
the functions may be called from
multiple threads etc).</li>
<li>I thought of making the client supply
some "status" object that can be
inspected after the call, but that
would make the API quite ugly.</li>
</ul>

So what's your take on the subject ? How do you report errors in a clean way ?

Error reporting in a C library

我正在寻找一种健壮的方式来报告C库中的错误。考虑一个简单的队列示例：struct queue *q = malloc(sizeof(*q));if (NULL == q) {    /* malloc failed. now what ? */    return NULL; /* maybe ? */}好的，对于这个...

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