什么是pkg-config？为什么使用pkg-config？

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，使用这个工具，我们可以很方便地编译一个项目。

为什么使用pkg-config

在linux中，经常会安装很多第三方的模块，我们在编译链接他们的时候需要制定头文件、库文件的位置，以及库文件的名字等等。

就以OpenCV为例子，如果我们用g++编译，就需要指定头文件库文件的相关信息，但是因为OpenCV依赖的库文件很多，我们指定的时候需要链接很多库，这就很麻烦了，比如

g++ DisplayImage.cpp -I/usr/local/include/opencv4/opencv -I/usr/local/include/opencv4 -L/usr/local/lib -lopencv_gapi -lopencv_stitching -lopencv_aruco -lopencv_bgsegm -lopencv_bioinspired -lopencv_ccalib -lopencv_cudabgsegm -lopencv_cudafeatures2d -lopencv_cudaobjdetect -lopencv_cudastereo -lopencv_dnn_objdetect -lopencv_dnn_superres -lopencv_dpm -lopencv_highgui -lopencv_face -lopencv_freetype -lopencv_fuzzy -lopencv_hfs -lopencv_img_hash -lopencv_line_descriptor -lopencv_quality -lopencv_reg -lopencv_rgbd -lopencv_saliency -lopencv_stereo -lopencv_structured_light -lopencv_phase_unwrapping -lopencv_superres -lopencv_cudacodec -lopencv_surface_matching -lopencv_tracking -lopencv_datasets -lopencv_text -lopencv_dnn -lopencv_plot -lopencv_videostab -lopencv_cudaoptflow -lopencv_optflow -lopencv_cudalegacy -lopencv_videoio -lopencv_cudawarping -lopencv_xfeatures2d -lopencv_shape -lopencv_ml -lopencv_ximgproc -lopencv_video -lopencv_xobjdetect -lopencv_objdetect -lopencv_calib3d -lopencv_imgcodecs -lopencv_features2d -lopencv_flann -lopencv_xphoto -lopencv_photo -lopencv_cudaimgproc -lopencv_cudafilters -lopencv_imgproc -lopencv_cudaarithm -lopencv_core -lopencv_cudev

用pkg-config就可以解决这个问题，使用很简单：

g++ DisplayImage.cpp $(pkg-config --cflags --libs opencv4)

其实就是用pkg-config --cflags --libs opencv4这个命令代替了-I -L -lxxx.so等指令。

其实构建OpenCV项目还有一种方法是cmake，关于cmake的使用方法，我们以后再介绍。

怎么使用pkg-config

这篇文建是就是根据官方文档介绍写的，大家以后需要安装什么模块，查看使用方法的，尽量都去官网看一看。

pc文件

pkg-config读后缀为pc的配置文件的，pkg-config怎么知道pc文件在哪呢？有两个方法

1 官网中这样说的

On a typical Unix system, it will search in the directories /usr/lib/pkgconfig and /usr/share/pkgconfig

所以pc文件的路径就在

• /usr/lib/pkgconfig
• /usr/share/pkgconfig 这两个目录下。

2 第二种就是修改PKG_CONFIG_PATH环境变量，将pc文件的路径添加到这个环境变量中

我们可以执行pkg-config --variable pc_path pkg-config来查看当前pkg-config会搜索的路径

示例

接下来我们以opencv4.pc来简单介绍下。

# Package Information for pkg-config


prefix=/usr/local
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir_old=${prefix}/include/opencv4/opencv
includedir_new=${prefix}/include/opencv4


Name: OpenCV
Description: Open Source Computer Vision Library
Version: 4.2.0
Libs: -L${exec_prefix}/lib -lopencv_gapi -lopencv_stitching -lopencv_aruco -lopencv_bgsegm -lopencv_bioinspired -lopencv_ccalib -lopencv_cudabgsegm -lopencv_cudafeatures2d -lopencv_cudaobjdetect -lopencv_cudastereo -lopencv_dnn_objdetect -lopencv_dnn_superres -lopencv_dpm -lopencv_highgui -lopencv_face -lopencv_freetype -lopencv_fuzzy -lopencv_hfs -lopencv_img_hash -lopencv_line_descriptor -lopencv_quality -lopencv_reg -lopencv_rgbd -lopencv_saliency -lopencv_stereo -lopencv_structured_light -lopencv_phase_unwrapping -lopencv_superres -lopencv_cudacodec -lopencv_surface_matching -lopencv_tracking -lopencv_datasets -lopencv_text -lopencv_dnn -lopencv_plot -lopencv_videostab -lopencv_cudaoptflow -lopencv_optflow -lopencv_cudalegacy -lopencv_videoio -lopencv_cudawarping -lopencv_xfeatures2d -lopencv_shape -lopencv_ml -lopencv_ximgproc -lopencv_video -lopencv_xobjdetect -lopencv_objdetect -lopencv_calib3d -lopencv_imgcodecs -lopencv_features2d -lopencv_flann -lopencv_xphoto -lopencv_photo -lopencv_cudaimgproc -lopencv_cudafilters -lopencv_imgproc -lopencv_cudaarithm -lopencv_core -lopencv_cudev
Libs.private: -lm -lpthread -lcudart_static -ldl -lrt -lnppc -lnppial -lnppicc -lnppicom -lnppidei -lnppif -lnppig -lnppim -lnppist -lnppisu -lnppitc -lnpps -lcublas -lcudnn -lcufft -L-L/usr/local/cuda -llib64 -L-L/usr/lib -lx86_64-linux-gnu
Cflags: -I${includedir_old} -I${includedir_new}

1 参数说明

• Name：模块的名字OpenCV，注意，pkg-config是按照文件名字来查找，和这儿的name无关
• Description：简单的描述
• Version：模块的版本信息
• Libs：模块依赖的lib的信息
• Libs.private：木块需要但是并未公开出炉的链接库
• Cflags：模块的编译器标志

2 执行

$ pkg-config  --modversion opencv4
4.2.0


$ pkg-config  --cflags opencv4
-I/usr/local/include/opencv4/opencv -I/usr/local/include/opencv4


$ pkg-config  --libs opencv4
-L/usr/local/lib -lopencv_gapi -lopencv_stitching -lopencv_aruco -lopencv_bgsegm -lopencv_bioinspired -lopencv_ccalib -lopencv_cudabgsegm -lopencv_cudafeatures2d -lopencv_cudaobjdetect -lopencv_cudastereo -lopencv_dnn_objdetect -lopencv_dnn_superres -lopencv_dpm -lopencv_highgui -lopencv_face -lopencv_freetype -lopencv_fuzzy -lopencv_hfs -lopencv_img_hash -lopencv_line_descriptor -lopencv_quality -lopencv_reg -lopencv_rgbd -lopencv_saliency -lopencv_stereo -lopencv_structured_light -lopencv_phase_unwrapping -lopencv_superres -lopencv_cudacodec -lopencv_surface_matching -lopencv_tracking -lopencv_datasets -lopencv_text -lopencv_dnn -lopencv_plot -lopencv_videostab -lopencv_cudaoptflow -lopencv_optflow -lopencv_cudalegacy -lopencv_videoio -lopencv_cudawarping -lopencv_xfeatures2d -lopencv_shape -lopencv_ml -lopencv_ximgproc -lopencv_video -lopencv_xobjdetect -lopencv_objdetect -lopencv_calib3d -lopencv_imgcodecs -lopencv_features2d -lopencv_flann -lopencv_xphoto -lopencv_photo -lopencv_cudaimgproc -lopencv_cudafilters -lopencv_imgproc -lopencv_cudaarithm -lopencv_core -lopencv_cudev

最后再来看一下编译的指令，是不是就简单了呢

g++ DisplayImage.cpp $(pkg-config --cflags --libs opencv4)

审核编辑：刘清