什么是pkg-config

pkg-config是一個linux下的命令，用于獲得某一個庫/模塊的所有編譯相關(guān)的信息，使用這個工具，我們可以很方便地編譯一個項目。

為什么使用pkg-config

在linux中，經(jīng)常會安裝很多第三方的模塊，我們在編譯鏈接他們的時候需要制定頭文件、庫文件的位置，以及庫文件的名字等等。

就以O(shè)penCV為例子，如果我們用g++編譯，就需要指定頭文件庫文件的相關(guān)信息，但是因為OpenCV依賴的庫文件很多，我們指定的時候需要鏈接很多庫，這就很麻煩了，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就可以解決這個問題，使用很簡單：

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

其實就是用pkg-config --cflags --libs opencv4這個命令代替了-I -L -lxxx.so等指令。

其實構(gòu)建OpenCV項目還有一種方法是cmake，關(guān)于cmake的使用方法，我們以后再介紹。

怎么使用pkg-config

這篇文建是就是根據(jù)官方文檔介紹寫的，大家以后需要安裝什么模塊，查看使用方法的，盡量都去官網(wǎng)看一看。

pc文件

pkg-config讀后綴為pc的配置文件的，pkg-config怎么知道pc文件在哪呢？有兩個方法

1 官網(wǎng)中這樣說的

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

所以pc文件的路徑就在

• /usr/lib/pkgconfig
• /usr/share/pkgconfig 這兩個目錄下。

2 第二種就是修改PKG_CONFIG_PATH環(huán)境變量，將pc文件的路徑添加到這個環(huán)境變量中

我們可以執(zhí)行pkg-config --variable pc_path pkg-config來查看當(dāng)前pkg-config會搜索的路徑

示例

接下來我們以opencv4.pc來簡單介紹下。

# 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 參數(shù)說明

• Name：模塊的名字OpenCV，注意，pkg-config是按照文件名字來查找，和這兒的name無關(guān)
• Description：簡單的描述
• Version：模塊的版本信息
• Libs：模塊依賴的lib的信息
• Libs.private：木塊需要但是并未公開出爐的鏈接庫
• Cflags：模塊的編譯器標(biāo)志

2 執(zhí)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

最后再來看一下編譯的指令，是不是就簡單了呢

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

審核編輯：劉清