blocks|key|408401|text|您正在使用的boost库依赖于boost_system库。(并不是所有人都这样。)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|408402|假设您使用的是gcc，请尝试将-lboost_system添加到您的编译器命令行，以便链接到该库。|offset|length|style|CODE|408403|entityMap^0|0|F|E|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

The boost library you are using depends on the boost_system library. (Not all of them do.)

Assuming you use gcc, try adding <code>-lboost_system</code> to your compiler command line in order to link against that library.

blocks|key|623876|text|与定义缺失符号(-lboost_system)的库链接是显而易见的解决方案，但在Boost.System的特殊情况下，原始设计中的错误功能使其不必要地使用boost::system::generic_category()和boost::system::system_category()。使用标志-DBOOST_SYSTEM_NO_DEPRECATED进行编译会禁用该代码，并允许在不需要-lboost_system的情况下编译大量程序(如果显式使用库的某些特性，当然仍然需要该链接)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|623877|从Boost+1.66和this+commit开始，这种行为现在是默认的，所以希望越来越少的用户需要这个答案。|623878|正如@AndrewMarshall所指出的，另一种选择是定义BOOST_ERROR_CODE_HEADER_ONLY，它启用代码的仅头版本。这是Boost的discouraged，因为它会破坏一些功能。然而，从1.69开始，header-only似乎有become+the+default，这使得这个问题变得过时了。|623879|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/boostorg/system/commit/829a1320a7bef3ade74d6691fdcfe72e0b6917e9|1|https://lists.boost.org/Archives/boost/2017/10/239106.php|2|https://www.boost.org/doc/libs/1_71_0/libs/system/doc/html/system.html#changes_in_boost_1_69^0|8|E|25|X|33|W|44|S|5E|E|0|C|B|0|0|U|S|26|B|1|3I|I|2|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|16|8|@]|D|@$9|17|A|18|1|19]]|E|$]]|$1|H|3|I|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@$9|1D|A|1E|1|1F]|$9|1G|A|1H|1|1I]]|E|$]]|$1|J|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]|R|$5|M|N|O|E|$P|S]]|T|$5|M|N|O|E|$P|U]]]]

Linking with a library that defines the missing symbol (<code>-lboost_system</code>) is the obvious solution, but in the particular case of Boost.System, a misfeature in the original design makes it use <code>boost::system::generic_category()</code> and <code>boost::system::system_category()</code> needlessly. Compiling with the flag <code>-DBOOST_SYSTEM_NO_DEPRECATED</code> disables that code and lets a number of programs compile without requiring <code>-lboost_system</code> (that link is of course still needed if you explicitly use some of the library's features).

Starting from Boost 1.66 and <a href="https://github.com/boostorg/system/commit/829a1320a7bef3ade74d6691fdcfe72e0b6917e9" rel="noreferrer">this commit</a>, this behavior is now the default, so hopefully fewer and fewer users should need this answer.

As noticed by @AndrewMarshall, an alternative is to define <code>BOOST_ERROR_CODE_HEADER_ONLY</code> which enables a header-only version of the code. This was <a href="https://lists.boost.org/Archives/boost/2017/10/239106.php" rel="noreferrer">discouraged</a> by Boost as it can break some functionality. However, since 1.69, header-only seems to have <a href="https://www.boost.org/doc/libs/1_71_0/libs/system/doc/html/system.html#changes_in_boost_1_69" rel="noreferrer">become the default</a>, supposedly making this question obsolete.

blocks|key|408847|text|对于那些不需要整个shebang的人来说，另一个解决方法是:使用开关|type|unstyled|depth|inlineStyleRanges|entityRanges|data|408848|-DBOOST_ERROR_CODE_HEADER_ONLY。|offset|length|style|CODE|408849|如果你使用CMake，它就是add_definitions(-DBOOST_ERROR_CODE_HEADER_ONLY)。|408850|entityMap^0|0|0|U|0|E|1B|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@$D|N|E|O|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@$D|Q|E|R|F|G]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|K|$]]

Another workaround for those who don't need the entire shebang: use the switch 

<code>-DBOOST_ERROR_CODE_HEADER_ONLY</code>. 

If you use CMake, it's <code>add_definitions(-DBOOST_ERROR_CODE_HEADER_ONLY)</code>.

blocks|key|408475|text|上面的错误是一个链接器错误...链接器a+program+that+takes+one+or+more+objects+generated+by+a+compiler+and+combines+them+into+a+single+executable+program.|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|408476|您必须将-lboost_system添加到链接器标志中，该标志指示链接器必须在库libboost_system.so中查找类似于boost::system::system_category()的符号。|style|CODE|408477|如果使用main.cpp，请执行以下任一操作：|408478|g%2B%2B+main.cpp+-o+main+-lboost_system|code-block|syntax|javascript|408479|或|408480|g%2B%2B+-c+-o+main.o+main.cpp
g%2B%2B+main.o+-lboost_system|408481|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Linker_%2528computing%2529^0|J|38|0|0|4|E|14|I|1S|W|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@$A|15|B|16|F|G]|$A|17|B|18|F|G]|$A|19|B|1A|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|1B|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|1C|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1D|8|@]|9|@]|C|$]]|$1|Q|3|R|5|L|7|1E|8|@]|9|@]|C|$M|N]]|$1|S|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

The above error is a linker error... the linker <a href="http://en.wikipedia.org/wiki/Linker_%28computing%29" rel="nofollow noreferrer">a program that takes one or more objects generated by a compiler and combines them into a single executable program.</a>

You must add <code>-lboost_system</code> to you linker flags which indicates to the linker that it must look for symbols like <code>boost::system::system_category()</code> in the library <code>libboost_system.so</code>.

If you have main.cpp, either:

<pre><code>g++ main.cpp -o main -lboost_system
</code></pre>

OR

<pre><code>g++ -c -o main.o main.cpp
g++ main.o -lboost_system
</code></pre>

blocks|key|408727|text|使用CMAKE和find_package时，请确保：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|408728|find_package(Boost+COMPONENTS+system+...)|code-block|syntax|javascript|408729|而不是|408730|find_package(boost+COMPONENTS+system+...)|408731|有些人可能为此浪费了几个小时……|408732|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

When using CMAKE and find_package, make sure it is :

<pre><code>find_package(Boost COMPONENTS system ...)
</code></pre>

and not 

<pre><code>find_package(boost COMPONENTS system ...)
</code></pre>

Some people may have lost hours for that ...

blocks|key|408806|text|当我遇到这个问题时，原因是库的顺序。为了解决这个问题，我把libboost_system放在了最后：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|408807|g%2B%2B+mingw/timer1.o+-o+mingw/timer1.exe++-L/usr/local/boost_1_61_0/stage/lib+\
++++-lboost_timer-mgw53-mt-1_61+\
++++-lboost_chrono-mgw53-mt-1_61+\
++++-lboost_system-mgw53-mt-1_61|code-block|syntax|javascript|408808|这是在一个简单的计时器示例中，使用了名为gcc+5.3和boost+1.61.0的版本。|408809|entityMap^0|T|F|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

When I had this, problem, the cause was the ordering of the libraries. To fix it, I put <code>libboost_system</code> last:

<pre class="lang-sh prettyprint-override"><code>g++ mingw/timer1.o -o mingw/timer1.exe -L/usr/local/boost_1_61_0/stage/lib \
 -lboost_timer-mgw53-mt-1_61 \
 -lboost_chrono-mgw53-mt-1_61 \
 -lboost_system-mgw53-mt-1_61
</code></pre>

This was on mingw with gcc 5.3 and boost 1.61.0 with a simple timer example.

blocks|key|408611|text|在我的例子中，添加-lboost_system是不够的，它仍然无法在我的自定义构建环境中找到它。我不得不使用Get+rid+of+"gcc+-+/usr/bin/ld:+warning+lib+not+found"上的建议，并将我的./configure命令更改为：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|408612|./configure+CXXFLAGS="-I$HOME/include"+LDFLAGS="-L$HOME/lib+-Wl,-rpath-link,$HOME/lib"+--with-boost-libdir=$HOME/lib+--prefix=$HOME|code-block|syntax|javascript|408613|有关更多详细信息，请参阅Boost+1.51+:+"error:+could+not+link+against+boost_thread+!"|408614|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/13507600/get-rid-of-gcc-usr-bin-ld-warning-lib-not-found|1|https://stackoverflow.com/questions/12408564/boost-1-51-error-could-not-link-against-boost-thread/21957198#21957198^0|9|E|38|B|1I|1H|0|0|0|C|1N|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|15|8|@]|D|@$9|16|A|17|1|18]]|E|$]]|$1|M|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

in my case, adding <code>-lboost_system</code> was not enough, it still could not find it in my custom build environment. I had to use the advice at <a href="https://stackoverflow.com/questions/13507600/get-rid-of-gcc-usr-bin-ld-warning-lib-not-found">Get rid of &quot;gcc - /usr/bin/ld: warning lib not found&quot;</a> and change my <code>./configure</code> command to:

<pre><code>./configure CXXFLAGS="-I$HOME/include" LDFLAGS="-L$HOME/lib -Wl,-rpath-link,$HOME/lib" --with-boost-libdir=$HOME/lib --prefix=$HOME
</code></pre>

for more details see <a href="https://stackoverflow.com/questions/12408564/boost-1-51-error-could-not-link-against-boost-thread/21957198#21957198">Boost 1.51 : &quot;error: could not link against boost_thread !&quot;</a>

blocks|key|623744|text|...and如果你想静态链接你的main，在你的you文件中添加以下内容到需求中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|623745|<link>static
<library>/boost/system//boost_system|code-block|syntax|javascript|623746|也许还包括：|623747|<linkflags>-static-libgcc
<linkflags>-static-libstdc%2B%2B|623748|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

...and in case you wanted to link your main statically, in your Jamfile add the following to requirements:

<pre><code>&lt;link&gt;static
&lt;library&gt;/boost/system//boost_system
</code></pre>

and perhaps also:

<pre><code>&lt;linkflags&gt;-static-libgcc
&lt;linkflags&gt;-static-libstdc++
</code></pre>

I'm trying to compile a program on Ubuntu 11.10 that uses the Boost libraries. I have the 1.46-dev Boost libraries from the Ubuntu Repository installed, but I get an error when compiling the program.

<code>undefined reference to boost::system::system_category()</code>

What is it that I do wrong?

undefined reference to boost::system::system_category() when compiling

编译器

Ubuntu

我正在尝试在Ubuntu11.10上编译一个使用Boost库的程序。我安装了来自Ubuntu Repository的1.46-dev Boost库，但在编译该程序时出现错误。undefined reference to boost::system::system_category()我做错了什么？

问编译时对boost::system::system_category()的引用未定义
EN

回答 8

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