blocks|key|3395504|text|您可能会发现，无论您使用的是什么系统，都必须链接数学库，例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3395505|gcc+-o+myprog+myprog.c+-L/path/to/libs+-lm
+++++++++++++++++++++++++++++++++++++++%5E%5E%5E+-+this+bit+here.|code-block|syntax|javascript|3395506|包括头可以让编译器知道函数声明，但它不一定会自动链接到执行该函数所需的代码。|3395507|如果做不到这一点，你需要向我们展示你的代码，你的编译命令和你运行的平台(操作系统，编译器等)。|3395508|以下代码可以很好地编译和链接：|3395509|#include+<math.h>
int+main+(void)+{
++++int+max+=+sqrt+(9);
++++return+0;
}|3395510|3395511|请注意，有些编译系统依赖于在命令行上给出库的顺序。我的意思是，他们可能会按顺序处理这些库，并且只使用它们来满足序列中那个点上未解析的符号。|3395512|因此，例如，给定以下命令：|3395513|gcc+-o+plugh+plugh.o+-lxyzzy
gcc+-o+plugh+-lxyzzy+plugh.o|3395514|而且plugh.o需要xyzzy库中的一些东西，第二个可能不会像您期望的那样工作。在列出该库时，不存在需要满足的未解析符号。|offset|length|style|CODE|3395515|当来自plugh.o的未解析的符号出现时，为时已晚。|3395516|entityMap^0|0|0|0|0|0|0|0|0|0|0|2|7|B|5|0|3|7|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|17|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|18|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|19|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1C|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|1D|8|@]|9|@]|A|$]]|$1|T|3|U|5|D|7|1E|8|@]|9|@]|A|$E|F]]|$1|V|3|W|5|6|7|1F|8|@$X|1G|Y|1H|Z|10]|$X|1I|Y|1J|Z|10]]|9|@]|A|$]]|$1|11|3|12|5|6|7|1K|8|@$X|1L|Y|1M|Z|10]]|9|@]|A|$]]|$1|13|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|14|$]]

You may find that you have to link with the math libraries on whatever system you're using, something like:
<pre class="lang-none prettyprint-override"><code>gcc -o myprog myprog.c -L/path/to/libs -lm
 ^^^ - this bit here.
</code></pre>
Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function.
Failing that, you'll need to show us your code, your compile command and the platform you're running on (operating system, compiler, etc).
The following code compiles and links fine:
<pre><code>#include &lt;math.h&gt;
int main (void) {
 int max = sqrt (9);
 return 0;
}
</code></pre>
<hr />
Just be aware that some compilation systems depend on the order in which libraries are given on the command line. By that, I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence.
So, for example, given the commands:
<pre class="lang-none prettyprint-override"><code>gcc -o plugh plugh.o -lxyzzy
gcc -o plugh -lxyzzy plugh.o
</code></pre>
and <code>plugh.o</code> requires something from the <code>xyzzy</code> library, the second may not work as you expect. At the point where you list the library, there are no unresolved symbols to satisfy.
And when the unresolved symbols from <code>plugh.o</code> do appear, it's too late.

blocks|key|4995852|text|我想你已经用#include+<math.h>导入了math.h|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4995853|因此，我能看到的唯一其他原因是缺少链接信息的。您必须将代码与-lm选项链接起来。|BOLD|4995854|如果您只是尝试使用gcc编译一个文件，只需将-lm添加到您的命令行，否则，给出一些关于您的构建过程的信息。|4995855|entityMap^0|6|H|0|M|I|U|3|0|0|1H|M|3|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|P|8|@$9|Q|A|R|B|H]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|I|3|J|5|6|7|U|8|@$9|V|A|W|B|H]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$]]

I suppose you have imported math.h with <code>#include &lt;math.h&gt;</code>

So the only other reason I can see is a missing linking information. You must link your code with the <code>-lm</code> option.

If you're simply trying to compile one file with gcc, just add <code>-lm</code> to your command line, otherwise, give some informations about your building process.

blocks|key|1328490|text|我也有同样的问题，但我只是通过在运行我的代码的命令后添加-lm来解决它。举例说明。gcc代码.c+-lm|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1328491|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 had the same issue, but I simply solved it by adding -lm after the command that runs my code.
Example. 
gcc code.c -lm

blocks|key|4995905|text|只需在c源文件中添加#include+<math.h>，并在结尾处添加Makefile中的-lm就可以了。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4995906|++++gcc+-pthread+-o+p3+p3.c+-lm|code-block|syntax|javascript|4995907|entityMap^0|A|H|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Just adding the <code>#include &lt;math.h&gt;</code> in c source file and -lm in Makefile at the end will work for me.

<pre><code> gcc -pthread -o p3 p3.c -lm
</code></pre>

blocks|key|3395640|text|这里是我的观察，首先你需要包括头math.h作为math.h头文件中声明的sqrt()函数。例如，用于|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3395641|#include+<math.h>|code-block|syntax|javascript|3395642|其次，如果你阅读了sqrt的手册页面，你会注意到这一行链接到-lm。|BOLD|3395643|#include+<math.h>+/*+header+file+you+need+to+include+*/

double+sqrt(double+x);+/*+prototype+of+sqrt()+function+*/

Link+with+-lm.+/*+Library+linking+instruction+*/|3395644|3395645|，但应用程序仍未定义对sqrt的引用。你看到这里有什么问题吗？|blockquote|3395646|3395647|3395648|编译器错误是正确的，因为你没有将你的程序链接到库lm+&链接器无法找到sqrt()的引用，你需要显式地链接它。例如，用于|3395649|gcc+-Wall+-Wextra+-Werror+-pedantic+test.c+-lm|3395650|entityMap|0|LINK|mutability|MUTABLE|url|http://man7.org/linux/man-pages/man3/sqrt.3.html^0|G|6|O|6|11|6|0|0|R|7|9|4|0|0|0|0|0|0|0|O|2|Z|6|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]|$9|1A|A|1B|B|C]|$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1F|8|@$9|1G|A|1H|B|M]]|D|@$9|1I|A|1J|1|1K]]|E|$]]|$1|N|3|O|5|H|7|1L|8|@]|D|@]|E|$I|J]]|$1|P|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]|$1|Q|3|R|5|S|7|1N|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1O|8|@]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]|$1|V|3|W|5|6|7|1Q|8|@$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]]|D|@]|E|$]]|$1|X|3|Y|5|H|7|1V|8|@]|D|@]|E|$I|J]]|$1|Z|3|-4|5|6|7|1W|8|@]|D|@]|E|$]]]|10|$11|$5|12|13|14|E|$15|16]]]]

Here are my observation, firstly you need to include the header <code>math.h</code> as <code>sqrt()</code> function declared in <code>math.h</code> header file. For e.g

<pre><code>#include &lt;math.h&gt;
</code></pre>

secondly, if you read manual page of <a href="http://man7.org/linux/man-pages/man3/sqrt.3.html" rel="nofollow noreferrer">sqrt</a> you will notice this line Link with -lm.

<pre><code>#include &lt;math.h&gt; /* header file you need to include */

double sqrt(double x); /* prototype of sqrt() function */

Link with -lm. /* Library linking instruction */
</code></pre>

<blockquote>
 But application still says undefined reference to sqrt. Do you see any
 problem here? 
</blockquote>

Compiler error is correct as you haven't linked your program with library <code>lm</code> &amp; linker is unable to find reference of <code>sqrt()</code>, you need to link it explicitly. For e.g

<pre><code>gcc -Wall -Wextra -Werror -pedantic test.c -lm
</code></pre>

I have this simple code:

<pre><code>max = (int) sqrt (number);
</code></pre>

and in the header I have:

<pre><code>#include &lt;math.h&gt;
</code></pre>

But application still says undefined reference to <code>sqrt</code>. Do you see any problem here? It looks like everything should be okay.

Undefined reference to sqrt (or other mathematical functions)

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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我有这个简单的代码：max = (int) sqrt (number);在标题中，我有：#include <math.h>但应用程序仍然显示未定义的对sqrt的引用。你看到这里有什么问题吗？看起来一切都会好起来的。

问对sqrt (或其他数学函数)的引用未定义
EN

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问对sqrt (或其他数学函数)的引用未定义EN