在程序编译时候，通常需要引用外部库文件或者头文件，文件多了用gcc指定时候就显得麻烦，一个一个写在Makefile中也比较繁琐，这种情况下，能自动获取完整的依赖库信息就显得轻松不少了。

pkg-config简介及用法

关于pkg-config

pkg-config就是自动获取所需的库文件以及头文件的命令，原本设计用于Linux，不过后来其他系统如Win和Mac里也都有可用的版本。 主要用于输出C/C++的编译器需要的参数，链接器需要的参数以及已经安装软件版本等信息。

主要用法

其主要的命令参数以及解释如下:

Usage:
  pkg-config [OPTION...]

Help Options:
  -h, --help                              Show help options

Application Options:
  --version                               output version of pkg-config
  --modversion                            output version for package
  --atleast-pkgconfig-version=VERSION     require given version of pkg-config
  --libs                                  output all linker flags
  --static                                output linker flags for static linking
  --short-errors                          print short errors
  --libs-only-l                           output -l flags
  --libs-only-other                       output other libs (e.g. -pthread)
  --libs-only-L                           output -L flags
  --cflags                                output all pre-processor and compiler flags
  --cflags-only-I                         output -I flags
  --cflags-only-other                     output cflags not covered by the cflags-only-I option
  --variable=NAME                         get the value of variable named NAME
  --define-variable=NAME=VALUE            set variable NAME to VALUE
  --exists                                return 0 if the module(s) exist
  --print-variables                       output list of variables defined by the module
  --uninstalled                           return 0 if the uninstalled version of one or more module(s) or their dependencies will be used
  --atleast-version=VERSION               return 0 if the module is at least version VERSION
  --exact-version=VERSION                 return 0 if the module is at exactly version VERSION
  --max-version=VERSION                   return 0 if the module is at no newer than version VERSION
  --list-all                              list all known packages
  --debug                                 show verbose debug information
  --print-errors                          show verbose information about missing or conflicting packages (default unless --exists or --atleast/exact/max-version given on the command line)
  --silence-errors                        be silent about errors (default when --exists or --atleast/exact/max-version given on the command line)
  --errors-to-stdout                      print errors from --print-errors to stdout not stderr
  --print-provides                        print which packages the package provides
  --print-requires                        print which packages the package requires
  --print-requires-private                print which packages the package requires for static linking
  --validate                              validate a package's .pc file
  --define-prefix                         try to override the value of prefix for each .pc file found with a guesstimated value based on the location of the .pc file
  --dont-define-prefix                    don't try to override the value of prefix for each .pc file found with a guesstimated value based on the location of the .pc file
  --prefix-variable=PREFIX                set the name of the variable that pkg-config automatically sets

其中用的比较多的就是--cflags和--libs。主要用来输出头文件和lib文件。
如查找opencv头文件和lib库的位置:

bash
pkg-config --cflags --libs opencv

输出:

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

再如Gstreamer的:

bash
pkg-config --cflags --libs gstreamer-1.0

可以看到,

-pthread -I/usr/include/gstreamer-1.0 -I/usr/lib/x86_64-linux-gnu/gstreamer-1.0/include -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -lgstreamer-1.0 -lgobject-2.0 -lglib-2.0

关于路径的获取

pkg-config获取路径是通过查询第三方库的pc文件实现的。比如:

bash
cd /usr/local/lib/pkgconfig
ls

输出:

flann.pc       libavdevice.pc  libavformat.pc  libswresample.pc  opencv.pc
libavcodec.pc  libavfilter.pc  libavutil.pc    libswscale.pc

pc文件内容通常包含Name, Description, Version, Libs, Cflags等基本参数。如opencv的pc文件内容是:

# Package Information for pkg-config

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

Name: OpenCV
Description: Open Source Computer Vision Library
Version: 3.2.0
Libs: -L${exec_prefix}/lib -lopencv_cudabgsegm -lopencv_cudaobjdetect -lopencv_cudastereo -lopencv_stitching -lopencv_cudafeatures2d -lopencv_superres -lopencv_cudacodec -lopencv_videostab -lopencv_cudaoptflow -lopencv_cudalegacy -lopencv_cudawarping -lopencv_aruco -lopencv_bgsegm -lopencv_bioinspired -lopencv_ccalib -lopencv_dpm -lopencv_freetype -lopencv_fuzzy -lopencv_line_descriptor -lopencv_optflow -lopencv_reg -lopencv_saliency -lopencv_stereo -lopencv_structured_light -lopencv_phase_unwrapping -lopencv_rgbd -lopencv_surface_matching -lopencv_tracking -lopencv_datasets -lopencv_text -lopencv_face -lopencv_plot -lopencv_dnn -lopencv_xfeatures2d -lopencv_shape -lopencv_video -lopencv_ximgproc -lopencv_calib3d -lopencv_features2d -lopencv_flann -lopencv_xobjdetect -lopencv_objdetect -lopencv_ml -lopencv_xphoto -lopencv_highgui -lopencv_videoio -lopencv_photo -lopencv_imgcodecs -lopencv_cudaimgproc -lopencv_cudafilters -lopencv_imgproc -lopencv_cudaarithm -lopencv_core -lopencv_cudev
Libs.private: -L/usr/lib/x86_64-linux-gnu -lpng -lz -ltiff -ljasper -ljpeg -lgtk-x11-2.0 -lgdk-x11-2.0 -lpangocairo-1.0 -latk-1.0 -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lpangoft2-1.0 -lpango-1.0 -lgobject-2.0 -lglib-2.0 -lfontconfig -lfreetype -lgthread-2.0 -ldc1394 -lavcodec-ffmpeg -lavformat-ffmpeg -lavutil-ffmpeg -lswscale-ffmpeg -ldl -lm -lpthread -lrt -lcudart -lnppc -lnppi -lnpps -lcufft -L-L/usr/local/cuda -l64
Cflags: -I${includedir_old} -I${includedir_new}

所以也可以以同样的方式添加自己的第三方库来简化编译工作。