Linux静态库与动态库实例详解
<p><strong>Linux静态库与动态库实例详解</strong></p>
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1. Linux 下静态链接库编译与使用</p>
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首先编写如下代码：</p>
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<code class="bash plain">//</code> <code class="bash plain">main.c</code>
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<code class="bash comments">#include "test.h"</code>
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<code class="bash plain">int main(){</code>
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<code class="bash spaces"> </code><code class="bash functions">test</code><code class="bash plain">();</code>
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<code class="bash spaces"> </code><code class="bash keyword">return</code> <code class="bash plain">0; </code>
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<code class="bash plain">}</code>
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<code class="bash plain">//</code> <code class="bash functions">test</code><code class="bash plain">.h</code>
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<code class="bash comments">#include<iostream></code>
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<code class="bash plain">using namespace std;</code>
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<code class="bash plain">void </code><code class="bash functions">test</code><code class="bash plain">();</code>
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<code class="bash plain">//</code> <code class="bash functions">test</code><code class="bash plain">.c</code>
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<code class="bash comments">#include "test.h"</code>
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<code class="bash plain">void </code><code class="bash functions">test</code><code class="bash plain">(){</code>
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<code class="bash spaces"> </code><code class="bash plain">cout<< </code><code class="bash string">"test!"</code> <code class="bash plain"><<endl;</code>
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<code class="bash plain">}</code>
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然后编译：</p>
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1. gcc -c test.c //生成目标文件<br>
2. ar crv libtest.a test.o //生成静态链接库libtest.a<br>
3. g++ -o main main.c -ltest //编译main程序同时链接libtest.a静态库<br>
4. ./main //运行main程序</p>
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2. Linux 下动态链接库编译与使用</p>
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代码与上述一致。</p>
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然后编译：</p>
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1. g++ -fPIC -shared -o libtest.so test.c //生成动态链接库libtest.so<br>
2. g++ -o main main.c -ltest //调用动态链接库libtest.so<br>
3. ./main //运行main程序</p>
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3. 链接时缺失了相关目标文件（.o）</p>
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代码与上述一致。</p>
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编译过程如下：</p>
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1. gcc -c test.c<br>
2. gcc -c main.c<br>
3. gcc -o main main.o</p>
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这时，你会发现，报错了：undefined reference to `test'.</p>
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这就是最典型的 undefined reference 错误,因为在链接时发现找不到某个函数的实现文件， 本例中test.o文件中包含了test()函数的实现，所以如果按下面这种方式链接就没事了。</p>
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<code class="bash plain">1. gcc -o main main.o </code><code class="bash functions">test</code><code class="bash plain">.o</code>
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<code class="bash plain">【扩展】：其实上面为了让大家更加清楚底层原因，我把编译链接分开了，下面这样编译</code>
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<code class="bash plain">也会报undefined reference错，其实底层原因与上面是一样的。</code>
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<code class="bash plain">gcc -o main main.c </code><code class="bash plain">//</code><code class="bash plain">缺少</code><code class="bash functions">test</code><code class="bash plain">()的实现文件 </code>
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<code class="bash plain">需要改成如下形式才能成功，将</code><code class="bash functions">test</code><code class="bash plain">()函数的实现文件一起编译。</code>
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<code class="bash plain">gcc -o main main.c </code><code class="bash functions">test</code><code class="bash plain">.c </code><code class="bash plain">//ok</code><code class="bash plain">,没问题了</code>
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4. 链接时缺少相关的库文件（.a/.so）</p>
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<code class="bash plain">在此，只举个静态库的例子，假设源码与上述一致。</code>
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<code class="bash plain">1. 把</code><code class="bash functions">test</code><code class="bash plain">.c编译成静态库：</code>
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<code class="bash spaces"> </code><code class="bash plain">gcc -c </code><code class="bash functions">test</code><code class="bash plain">.c</code>
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<code class="bash spaces"> </code><code class="bash plain">sr -rc </code><code class="bash functions">test</code><code class="bash plain">.a </code><code class="bash functions">test</code><code class="bash plain">.o</code>
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<code class="bash spaces"> </code><code class="bash plain">gcc -c main.c</code>
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<code class="bash plain">2. 生成可执行程序：</code>
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<code class="bash spaces"> </code><code class="bash plain">gcc -o main -main.o</code>
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<code class="bash spaces"> </code><code class="bash plain">此时同样出现 undefined reference to `</code><code class="bash functions">test</code><code class="bash plain">'报错。其根本原因也是找不到</code><code class="bash functions">test</code><code class="bash plain">()函数的实现文</code>
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<code class="bash spaces"> </code><code class="bash plain">件，由于该</code><code class="bash functions">test</code><code class="bash plain">()函数的实现在</code><code class="bash functions">test</code><code class="bash plain">.a这个静态库中的，故在链接的时候需要在其后加入</code><code class="bash functions">test</code><code class="bash plain">.a这个</code>
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<code class="bash spaces"> </code><code class="bash plain">库，链接命令修改为如下形式即可。</code>
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<code class="bash spaces"> </code><code class="bash plain">1. gcc -o main main.c .</code><code class="bash plain">/test</code><code class="bash plain">.a</code>
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5. 多个库文件链接顺序问题</p>
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<code class="bash plain">这种问题也非常的隐蔽，不仔细研究你可能会感到非常地莫名其妙。我们依然回到第3小节所讨论</code>
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<code class="bash plain">的问题中，在最后，如果我们把链接的库的顺序换一下，看看会发生什么结果？</code>
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<code class="bash plain">1. gcc -o main main.o func.a </code><code class="bash functions">test</code><code class="bash plain">.a</code>
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<code class="bash plain">我们会得到如下的编译错误：</code>
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<code class="bash plain">1. </code><code class="bash functions">test</code><code class="bash plain">.a(</code><code class="bash functions">test</code><code class="bash plain">.o): In </code><code class="bash keyword">function</code> <code class="bash plain">`</code><code class="bash functions">test</code><code class="bash plain">': </code>
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<code class="bash plain">2. </code><code class="bash functions">test</code><code class="bash plain">.c:(.text+0x13): undefined reference to `func' </code>
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<code class="bash plain">3. collect2: ld returned 1 </code><code class="bash functions">exit</code> <code class="bash plain">status </code>
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<code class="bash plain">因此，我们需要注意，在链接命令中给出所依赖的库时，需要注意库之间的依赖顺序，依赖其他库</code>
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<code class="bash plain">的库一定要放到被依赖库的前面，这样才能真正避免undefined reference的错误，完成编译链接。</code>
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如有疑问请留言或者到本站社区交流讨论，感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！</p>
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原文链接：http://blog.csdn.net/u013709270/article/details/53264141</p>
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