pkg-config的安装配置及使用方法（转）

码字不易，转载请注明出处喔~~ 
原文网址：http://blog.csdn.net/newchenxf/article/details/51750239

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1 什么是pkg-config

pkg-config是一个linux下的命令，用于获得某一个库/模块的所有编译相关的信息。 
例子：

pkg-config opencv –libs –cflags

结果：

<span style="color:#000000"><code>-I/usr/include/opencv

/usr/lib/x86_64-linux-gnu/libopencv_calib3d<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_contrib<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_core<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_features2d<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_flann<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_gpu<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_highgui<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_imgproc<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_legacy<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_ml<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_objdetect<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_ocl<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_photo<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_stitching<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_superres<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_ts<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_video<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_videostab<span style="color:#4f4f4f">.</span>so

-lopencv_calib3d -lopencv_contrib -lopencv_core -lopencv_features2d -lopencv_flann -lopencv_gpu -lopencv_highgui -lopencv_imgproc -lopencv_legacy -lopencv_ml -lopencv_objdetect -lopencv_ocl -lopencv_photo -lopencv_stitching -lopencv_superres -lopencv_ts -lopencv_video -lopencv_videostab</code></span>

2 为什么要有pkg-config

从上面的例子，可以看出，pkg-config给出了opencv的头文件和库的所有信息！ 
这有什么好处？ 

所有用opencv的其他程序，在编译时，只需要写“pkg-config opencv –libs –cflags”,而不需要自己去找opencv的头文件在哪里，要链接的库在哪里！省时省力！ 
如果你写了一个库，不管是静态的还是动态的，要提供给第三方使用，那除了给人家库/头文件，最好也写一个pc文件，这样别人使用就方便很多，不用自己再手动写依赖了你哪些库，只需要敲一个”pkg-config [YOUR_LIB] –libs –cflags”。 

3 pkg-config的信息从哪里来？

很简单，有2种路径： 
第一种：取系统的/usr/lib下的所有*.pc文件。 
第二种：PKG_CONFIG_PATH环境变量所指向的路径下的所有*.pc文件。

这些pc文件什么时候有的？都是在你安装某个库/模块的时候，添加的。比如你往系统安装opencv时，就会在/usr/lib/目录下，放一个opencv.pc。 
比如，我的PC是这样的。你可以看到，有各种各样的pc文件。

<span style="color:#000000"><code>chenxf@chenxf-PC:/usr/lib/x86_64-linux-gnu/pkgconfig$ ls
alsa<span style="color:#009900">.pc</span>  cairo-tee<span style="color:#009900">.pc</span> fontenc<span style="color:#009900">.pc</span>  gl<span style="color:#009900">.pc</span>  harfbuzz<span style="color:#009900">.pc</span> libdrm_radeon<span style="color:#009900">.pc</span>
libswscale<span style="color:#009900">.pc</span>  pixman-<span style="color:#006666">1.</span>pc x11-xcb<span style="color:#009900">.pc</span> xcb-sync<span style="color:#009900">.pc</span> xkbcommon<span style="color:#009900">.pc</span> xvmc<span style="color:#009900">.pc</span>
opencv<span style="color:#009900">.pc</span> cairo-xcb<span style="color:#009900">.pc</span> freetype2<span style="color:#009900">.pc</span> glu<span style="color:#009900">.pc</span> ice<span style="color:#009900">.pc</span> libfs<span style="color:#009900">.pc</span> 
libdrm<span style="color:#009900">.pc</span> libraw1394<span style="color:#009900">.pc</span> pciaccess<span style="color:#009900">.pc</span> xcb-shm<span style="color:#009900">.pc</span>
......</code></span>

那么，pc文件到底写了什么？ 
打开看看就知道啦。比如opencv.pc。

<span style="color:#000000"><code># Package <span style="color:#000088">Information</span> for pkg-config
prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib/x86_64-linux-gnu
includedir_old=${prefix}/include/opencv
includedir_new=${prefix}/include

Name: OpenCV
Description: <span style="color:#000088">Open</span> Source Computer Vision Library
<span style="color:#000088">Version</span>: <span style="color:#006666">2.4</span><span style="color:#006666">.8</span>
Libs: -L${libdir} ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_calib3d.so -lopencv_calib3d ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_contrib.so -lopencv_contrib ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_core.so -lopencv_core ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_features2d.so -lopencv_features2d ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_flann.so -lopencv_flann ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_gpu.so -lopencv_gpu ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_highgui.so -lopencv_highgui ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_imgproc.so -lopencv_imgproc ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_legacy.so -lopencv_legacy ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_ml.so -lopencv_ml ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_objdetect.so -lopencv_objdetect ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_ocl.so -lopencv_ocl ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_photo.so -lopencv_photo ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_stitching.so -lopencv_stitching ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_superres.so -lopencv_superres ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_ts.so -lopencv_ts ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_video.so -lopencv_video ${exec_prefix}/lib/x86_64-linux-gnu/libopencv_videostab.so -lopencv_videostab
Cflags: -<span style="color:#000088">I</span>${includedir_old} -<span style="color:#000088">I</span>${includedir_new}</code></span>

一目了然，就是存了所有opencv的头文件/库的路径信息。和第一步我们敲的”pkg-config opencv –libs –cflags”的结果，是一样一样的~~~

4 pkg-config都有哪些命令参数

所有参数，可以通过pkg-config –help来查看。 
但我觉得其实就3个参数有用。

4.1 “pkg-config [NAME] –cflags”，查看头文件信息。

(注意这里是2个“-”，不知道为啥我原文写2个“-”，生成文章时只有一个。。。囧。。。不管了，反正提醒你一下啦) 
例子：

chenxf@chenxf-PC:~$ pkg-config opencv –cflags

结果：

<span style="color:#000000"><code>-<span style="color:#009900">I</span>/usr/<span style="color:#000088">include</span>/opencv</code></span>

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4.2 pkg-config [NAME] –libs，查看库信息。

例子：

chenxf@chenxf-PC:~$ pkg-config opencv –libs

结果：

<span style="color:#000000"><code>/usr/lib/x86_64-linux-gnu/libopencv_calib3d<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_contrib<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_core<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_features2d<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_flann<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_gpu<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_highgui<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_imgproc<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_legacy<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_ml<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_objdetect<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_ocl<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_photo<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_stitching<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_superres<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_ts<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_video<span style="color:#4f4f4f">.</span>so /usr/lib/x86_64-linux-gnu/libopencv_videostab<span style="color:#4f4f4f">.</span>so -lopencv_calib3d -lopencv_contrib -lopencv_core -lopencv_features2d -lopencv_flann -lopencv_gpu -lopencv_highgui -lopencv_imgproc -lopencv_legacy -lopencv_ml -lopencv_objdetect -lopencv_ocl -lopencv_photo -lopencv_stitching -lopencv_superres -lopencv_ts -lopencv_video -lopencv_videostab</code></span>

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4.3 pkg-config –list-all。查看pkg-config的所有模块信息。

例子：

pkg-config –list-all

结果：

<span style="color:#000000"><code>libass                         libass - LibASS <span style="color:#000088">is</span> an SSA/ASS subtitles rendering <span style="color:#000088">library</span>
xext                           Xext - Misc X <span style="color:#000088">Extension</span> <span style="color:#000088">Library</span>
pthread-stubs                  pthread stubs - Stubs missing <span style="color:#000088">from</span> libc <span style="color:#000088">for</span> standard pthread functions
videoproto                     VideoProto - Video <span style="color:#000088">extension</span> headers
libxdot                        libxdot - <span style="color:#000088">Library</span> <span style="color:#000088">for</span> parsing graphs <span style="color:#000088">in</span> xdot format
gtk+-unix-print-<span style="color:#006666">2.0</span>            GTK+ - GTK+ Unix print support
opencv                         OpenCV - Open Source Computer Vision <span style="color:#000088">Library</span>
xcb-randr                      XCB RandR - XCB RandR <span style="color:#000088">Extension</span>
renderproto                    RenderProto - Render <span style="color:#000088">extension</span> headers
xcb-present                    XCB Present - XCB Present <span style="color:#000088">Extension</span>
gdk-<span style="color:#006666">2.0</span>                        GDK - GTK+ Drawing Kit (x11 target)
libavfilter                    libavfilter - FFmpeg audio/video filtering <span style="color:#000088">library</span>
glesv2                         glesv2 - Mesa OpenGL ES <span style="color:#006666">2.0</span> <span style="color:#000088">library</span>
xcursor                        Xcursor - X Cursor <span style="color:#000088">Library</span>
libavcodec                     libavcodec - FFmpeg codec <span style="color:#000088">library</span>
xi                             Xi - X Input <span style="color:#000088">Extension</span> <span style="color:#000088">Library</span>
xrandr                         Xrandr - X RandR <span style="color:#000088">Library</span></code></span>

5 如何添加自己的pc文件

如上文所说，有2种方式。 
1. 把你的pc文件，直接放到/usr/lib/…默认路径下。 
2. 把你的pc文件的路径写到PKG_CONFIG_PATH环境变量里。 
比如，你可以在/etc/.bashrc或者/home/chenxf/.bashrc的文件末尾添加：

PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/home/chenxf/ffmpeg_build/lib/pkgconfig 
export PKG_CONFIG_PATH

那么，pkg-config就会到/home/chenxf/ffmpeg_build/lib/pkgconfig寻找*.pc文件。

我猜你想问，那我这个pc文件何时生效呢？ 
答案是，如果是/usr/lib下，立马生效！！！如果在环境变量里，只要先source ~/.bashrc一下，让环境变量生成，也立马生效。 
并不需要什么pkg-config update啥命令，让其更新信息。 
其实每次你执行pkg-config，都会去遍历所有的*.pc文件。

6 如何自己写pkg-config的pc文件

其实很简单，只需要拿别人的pc文件改一改就行了。 
不过我还是提一下吧。 
pc文件的所有参数：

Name: 该模块的名字，比如你的pc名字是xxxx.pc，那么名字最好也是xxxx。 
Description: 模块的简单描述。上文pkg-config –list-all命令出来的结果，每个名字后面就是description。 
URL: 用户可以通过该URL获得更多信息，或者下载信息。也是辅助的，可要可不要。 
Version: 版本号。 
Requires: 该模块有木有依赖于其他模块。一般没有。 
Requires.private: 该模块有木有依赖于其他模块，并且还不需要第三方知道的。一般也没有。 
Conflicts: 有没有和别的模块冲突。常用于版本冲突。比如，Conflicts: bar < 1.2.3，表示和bar模块的1.2.3以下的版本有冲突。 
Cflags: 这个就很重要了。pkg-config的参数–cflags就指向这里。主要用于写本模块的头文件的路径。 
Libs: 也很重要，pkg-config的参数–libs就指向这里。主要用于写本模块的库/依赖库的路径。 
Libs.private: 本模块依赖的库，但不需要第三方知道。

其实必须写的只有5个。Name、Description、Version、Cflags、Libs。

我们举2个例子吧。一个动态库，一个静态库。

例子1 动态库的pc文件

假设我写了libfoo.so，我的库将会被安装到/usr/local/lib/，头文件会放到/usr/local/include/foo。那么，pc文件可以这么写。

<span style="color:#000000"><code>prefix=<span style="color:#008800">/usr/local</span>
exec_prefix=<span style="color:#4f4f4f">${</span>prefix}
includedir=<span style="color:#4f4f4f">${</span>prefix}/<span style="color:#000088">include</span>
libdir=<span style="color:#4f4f4f">${</span>exec_prefix}/lib

<span style="color:#009900">Name</span><span style="color:#009900">:</span> foo
<span style="color:#009900">Description</span><span style="color:#009900">:</span> <span style="color:#009900">The</span> foo library
<span style="color:#009900">Version</span><span style="color:#009900">:</span> <span style="color:#006666">1.0</span>.<span style="color:#006666">0</span>
<span style="color:#009900">Cflags</span><span style="color:#009900">:</span> -<span style="color:#009900">I</span><span style="color:#4f4f4f">${</span>includedir}/foo
<span style="color:#009900">Libs</span><span style="color:#009900">:</span> -<span style="color:#009900">L</span><span style="color:#4f4f4f">${</span>libdir} -lfoo</code></span>

例子2 静态库的pc文件

正如我的另一博文所说，静态库链接动态库时，如何使用该静态库，如果我有个静态库libXXX.a，它依赖了很多其他动态库libAA.so，libBB.so，那么第三方程序DD.c要使用libXXX.a时，编译时还得链接libAA.so，libBB.so。 
如何让第三方程序，可以不用操心我这个libXXX.a到底依赖了什么？很简答，就是我的libXXX.a写一个pc文件。

其实这个问题，就发生在我最近搞的ffmpeg事情上。 
我下载了ffmpg，按照guide编译好了。生成了ffmpeg，以及相关的库。

<span style="color:#000000"><code>chenxf@chenxf-PC:~/ffmpeg_build/lib$ ls
libavcodec.a  libavdevice.a  libavfilter.a  libavformat.a  libavutil.a  libpostproc.a   libswresample.a  libswscale.a  libx264.a  libx265.a  pkgconfig</code></span>

当我写了个程序，想使用libavcodec.a，却各种编译错误。

gcc test.c -o test -I/home/chenxf/ffmpeg_build/include/ -L/home/chenxf/ffmpeg_build/lib -lavcodec

/home/chenxf/ffmpeg_sources/ffmpeg/libavcodec/aacdec_template.c:1117：对‘pthread_once’未定义的引用 
/home/chenxf/ffmpeg_build/lib/libavcodec.a(aacdec_fixed.o)：在函数‘aac_decode_init’中： 
/home/chenxf/ffmpeg_sources/ffmpeg/libavcodec/aacdec_template.c:1117：对‘pthread_once’未定义的引用 
/home/chenxf/ffmpeg_build/lib/libavcodec.a(aacenc.o)：在函数‘aac_encode_init’中： 
/home/chenxf/ffmpeg_sources/ffmpeg/libavcodec/aacenc.c:1039：对‘pthread_once’未定义的引用 

我当时还百思不得其解，为何用编译好了的libavcodec.a，第三方的程序，还会跟什么pthread有关！！！ 
答案是，第三方程序，还要链接libpthread.so。 
那我如果编译第三方程序，还得一个个添加libavcodec.a锁依赖的库，岂不是累死了？！！！！

而其实，ffmpeg已经操心过这个事情了，它编译好了后，也生成了pc文件。就在“/home/chenxf/ffmpeg_build/lib/pkgconfig”

chenxf@chenxf-PC:~/ffmpeg_build/lib/pkgconfig$ ls 
libavcodec.pc libavdevice.pc libavfilter.pc libavformat.pc libavutil.pc libpostproc.pc libswresample.pc libswscale.pc x264.pc x265.pc

随便打开一个看看。 
libavcodec.pc

<span style="color:#000000"><code>prefix<span style="color:#4f4f4f">=</span>/home/chenxf/ffmpeg_build
exec_prefix<span style="color:#4f4f4f">=</span>${prefix}
libdir<span style="color:#4f4f4f">=</span>${prefix}/lib
includedir<span style="color:#4f4f4f">=</span>${prefix}/include

Name: libavcodec
Description: FFmpeg codec library
Version: <span style="color:#006666">57.38</span><span style="color:#006666">.100</span>
Requires: libswresample <span style="color:#4f4f4f">>=</span> <span style="color:#006666">2.0</span><span style="color:#006666">.101</span>, libavutil <span style="color:#4f4f4f">>=</span> <span style="color:#006666">55.22</span><span style="color:#006666">.101</span>
Requires<span style="color:#4f4f4f">.</span><span style="color:#000088">private</span>:
Conflicts:
Libs: -L${libdir}  -lavcodec -lXv -lX11 -lXext -lxcb -lXau -lXdmcp -lxcb-shm -lxcb -lXau -lXdmcp -lxcb-xfixes -lxcb-render -lxcb-shape -lxcb -lXau -lXdmcp -lxcb-shape -lxcb -lXau -lXdmcp -lX11 -lasound -L/home/chenxf/ffmpeg_build/lib -lx265 -lstdc<span style="color:#4f4f4f">++</span> -lm -lrt -ldl -L/home/chenxf/ffmpeg_build/lib -lx264 -lpthread -lm -ldl -lfreetype -lz -lpng12 -lass -lfontconfig -lenca -lm -lfribidi -lexpat -lfreetype -lz -lpng12 -lm -llzma -lz -pthread
Libs<span style="color:#4f4f4f">.</span><span style="color:#000088">private</span>:
Cflags: -I${includedir}
</code></span>

看到没，看到没？！这里已经把libavcodec.a的所有依赖库，全部列出来了！！！！ 
所以，我唯一要做的，就是把这些pc文件的路径，写到PKG_CONFIG_PATH。 
我就在/home/chenxf/.bashrc末行添加了

PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/home/chenxf/ffmpeg_build/lib/pkgconfig 
export PKG_CONFIG_PATH

然后

source /home/chenxf/.bashrc

然后重新编译我的代码，就通过了！！！！好开森的样子！！！！…………^^

gcc test.c -o test pkg-config libavcodec libavformat libavutil --cflags --libs