编译时pkg_config的用法
1 什么是pkg-config
pkg-config是一个linux下的命令，用于获得某一个库/模块的所有编译安装相关的信息。
例子：pkg-config opencv –libs –cflags
结果： -I/usr/include/opencv
/usr/lib/x86_64-linux-gnu/libopencv_calib3d.so /usr/lib/x86_64-linux-gnu/libopencv_contrib.so /usr/lib/x86_64-linux-gnu/libopencv_core.so /usr/lib/x86_64-linux-gnu/libopencv_features2d.so /usr/lib/x86_64-linux-gnu/libopencv_flann.so /usr/lib/x86_64-linux-gnu/libopencv_gpu.so /usr/lib/x86_64-linux-gnu/libopencv_highgui.so /usr/lib/x86_64-linux-gnu/libopencv_imgproc.so /usr/lib/x86_64-linux-gnu/libopencv_legacy.so /usr/lib/x86_64-linux-gnu/libopencv_ml.so /usr/lib/x86_64-linux-gnu/libopencv_objdetect.so /usr/lib/x86_64-linux-gnu/libopencv_ocl.so /usr/lib/x86_64-linux-gnu/libopencv_photo.so /usr/lib/x86_64-linux-gnu/libopencv_stitching.so /usr/lib/x86_64-linux-gnu/libopencv_superres.so /usr/lib/x86_64-linux-gnu/libopencv_ts.so /usr/lib/x86_64-linux-gnu/libopencv_video.so /usr/lib/x86_64-linux-gnu/libopencv_videostab.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
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！
使用和不适用的对比：
g++ -g test.cpp -o test -I /usr/local/ImageMagick/include/ImageMagick-7 -L /usr/local/ImageMagick/lib/ -lMagick++-7.Q16HDRI
g++ test.cpp `pkg-config --cflags --libs Magick++-7.Q16HDRI`特别在依赖第三库时：
如果Magick++-7.Q16HDRI依赖的库刚好被你的程序中使用和依赖，你将需要无休止的去查找依赖的库，而使用pkg-config，pkg-config将都会帮你搞定。
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，就会在你的安装目录下，放一个/usr/local/opencv/lib64/pkgconfig/opencv.pc。 （我的安装目录/usr/local/opencv/）
[root@localhost tmp]# ls /usr/local/opencv/lib64/pkgconfig/
opencv.pc
看看pc文件的具体内容
prefix=/usr/local/opencv
exec_prefix=${prefix}
libdir=${exec_prefix}/lib64
includedir_old=${prefix}/include/opencv
includedir_new=${prefix}/include
Name: OpenCV
Description: Open Source Computer Vision Library
Version: 3.4.0
Libs: -L${exec_prefix}/lib64 -lopencv_dnn -lopencv_ml -lopencv_objdetect -lopencv_shape -lopencv_stitching -lopencv_superres -lopencv_videostab -lopencv_calib3d -lopencv_features2d -lopencv_highgui -lopencv_videoio -lopencv_imgcodecs -lopencv_video -lopencv_photo -lopencv_imgproc -lopencv_flann -lopencv_core
Libs.private: -L${exec_prefix}/share/OpenCV/3rdparty/lib64 -littnotify -llibprotobuf -llibjpeg -llibwebp -llibtiff -llibjasper -lIlmImf -lgtk-x11-2.0 -lgdk-x11-2.0 -latk-1.0 -lgio-2.0 -lpangoft2-1.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lcairo -lpango-1.0 -lfontconfig -lfreetype -L/lib64 -lpng -lz -lgstbase-0.10 -lgstreamer-0.10 -lgobject-2.0 -lgmodule-2.0 -lgthread-2.0 -lxml2 -lglib-2.0 -lgstvideo-0.10 -lgstapp-0.10 -lgstriff-0.10 -lgstpbutils-0.10 -ldc1394 -lavcodec -lavformat -lavutil -lswscale -ldl -lm -lpthread -lrt
Cflags: -I${includedir_old} -I${includedir_new}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。
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“-”)
[root@localhost tmp]# pkg-config opencv --cflags
-I/usr/local/opencv/include/opencv -I/usr/local/opencv/include 4.2 pkg-config [NAME] –libs，查看库信息。
[root@localhost tmp]# pkg-config opencv --libs
-L/usr/local/opencv/lib64 -lopencv_dnn -lopencv_ml -lopencv_objdetect -lopencv_shape -lopencv_stitching -lopencv_superres -lopencv_videostab -lopencv_calib3d -lopencv_features2d -lopencv_highgui -lopencv_videoio -lopencv_imgcodecs -lopencv_video -lopencv_photo -lopencv_imgproc -lopencv_flann -lopencv_core 4.3 pkg-config –list-all。查看pkg-config的所有模块信息。
[root@localhost tmp]# pkg-config opencv --list-all
zlib zlib - zlib compression library
gio-unix-2.0 GIO unix specific APIs - unix specific headers for glib I/O library
xextproto XExtProto - XExt extension headers
libpostproc libpostproc - FFmpeg postprocessing library
cairo-xcb cairo-xcb - XCB surface backend for cairo graphics library
gstreamer-tag-0.10 GStreamer Tag Library - Tag base classes and helper functions
gio-2.0 GIO - glib I/O library
gstreamer-pbutils-0.10 GStreamer Base Utils Library - General utility functions
xf86bigfontproto XF86BigFontProto - XF86BigFont extension headers
libv4l1 libv4l1 - v4l1 compatibility library
libv4l2 libv4l2 - v4l2 device access library
libsystemd-daemon systemd - systemd Daemon Utility Library - deprecated
xf86dgaproto XF86DGAProto - XF86DGA extension headers
xcb-composite XCB Composite - XCB Composite Extension
gstreamer-plugins-base-0.10 GStreamer Base Plugins Libraries - Streaming media framework, base plugins libraries
harfbuzz-icu harfbuzz - HarfBuzz text shaping library ICU integration
libpng15 libpng - Loads and saves PNG files
libsystemd-id128 systemd - systemd 128 Bit ID Utility Library - deprecated
xinerama Xinerama - The Xinerama Library
gstreamer-netbuffer-0.10 GStreamer Network Buffer Library - Network buffer for use in network sources/sinks
cairo-ps cairo-ps - PostScript surface backend for cairo graphics library
xcb-xevie XCB Xevie - XCB Xevie Extension
libswscale libswscale - FFmpeg image rescaling library
gmodule-2.0 GModule - Dynamic module loader for GLib
libva-glx libva-glx - Userspace Video Acceleration (VA) glx interface
glib-2.0 GLib - C Utility Library
ImageMagick ImageMagick - ImageMagick - convert, edit, and compose images (ABI Q16HDRI)
x264 x264 - H.264 (MPEG4 AVC) encoder library
x265 x265 - H.265/HEVC video encoder
randrproto RandrProto - Randr extension headers
gstreamer-riff-0.10 GStreamer RIFF Library - RIFF helper functions
libv4l2rds libv4l2rds - v4l2 RDS decode library
xau Xau - X authorization file management libary
gstreamer-check-0.10 GStreamer check unit testing - Unit testing helper library for GStreamer modules
dmxproto DMXProto - DMX extension headers
cairo-egl cairo-egl - EGL functions for cairo graphics library
xcb-damage XCB Damage - XCB Damage Extension
fontsproto FontsProto - Fonts extension headers
libyami libyami - Intel open source media infrastructure base on libva.
xineramaproto XineramaProto - Xinerama extension headers
usbutils usbutils - USB device database
pango Pango - Internationalized text handling
MagickCore-7.Q16HDRI MagickCore - MagickCore - C API for ImageMagick (ABI Q16HDRI)
xcb-xvmc XCB XvMC - XCB XvMC Extension
libavdevice libavdevice - FFmpeg device handling library
MagickWand MagickWand - MagickWand - C API for ImageMagick (ABI Q16HDRI)
libdrm libdrm - Userspace interface to kernel DRM services
gstreamer-sdp-0.10 GStreamer SDP Library - SDP helper functions
osmesa osmesa - Mesa Off-screen Rendering library
pciaccess pciaccess - Library providing generic access to the PCI bus and devices.
presentproto PresentProto - Present extension headers
bash-completion bash-completion - programmable completion for the bash shell
gl gl - Mesa OpenGL library
xf86miscproto XF86MiscProto - XF86Misc extension headers
xproxymngproto XProxyManagementProtocol - X Proxy Management Protocol headers
fontutil FontUtil - Font utilities dirs
xshmfence xshmfence - The X Shared Memory Fence Library
wayland-client Wayland Client - Wayland client side library
glproto GLProto - GL extension headers
libpcrecpp libpcrecpp - PCRECPP - C++ wrapper for PCRE
gdk-pixbuf-2.0 GdkPixbuf - Image loading and scaling
pangoft2 Pango FT2 and Pango Fc - Freetype 2.0 and fontconfig font support for Pango
libavutil libavutil - FFmpeg utility library
gdk-pixbuf-xlib-2.0 GdkPixbuf Xlib - GdkPixbuf rendering for Xlib
ice ICE - X Inter Client Exchange Library
gmodule-no-export-2.0 GModule - Dynamic module loader for GLib
libdrm_nouveau libdrm_nouveau - Userspace interface to nouveau kernel DRM services
libavformat libavformat - FFmpeg container format library
xrender Xrender - X Render Library
libva libva - Userspace Video Acceleration (VA) core interface
wayland-server Wayland Server - Server side implementation of the Wayland protocol
bigreqsproto BigReqsProto - BigReqs extension headers
gnome-video-effects gnome-video-effects - A collection of GStreamer effects to be used in different GNOME Modules
icu-io icu-io - International Components for Unicode: Stream and I/O Library
xproto Xproto - Xproto headers
liblzma liblzma - General purpose data compression library
xext Xext - Misc X Extension Library
xcb XCB - X-protocol C Binding
xcb-record XCB Record - XCB Record Extension
Magick++ Magick++ - Magick++ - C++ API for ImageMagick (ABI Q16HDRI)
pthread-stubs pthread stubs - Stubs missing from libc for standard pthread functions
xcb-xtest XCB XTEST - XCB XTEST Extension
videoproto VideoProto - Video extension headers
gtk+-unix-print-2.0 GTK+ - GTK+ Unix print support
gstreamer-audio-0.10 GStreamer Audio library - Audio helper functions and base classes
opencv OpenCV - Open Source Computer Vision Library
python-2.7 Python - Python library
xcb-randr XCB RandR - XCB RandR Extension
gstreamer-controller-0.10 GStreamer controller - Dynamic parameter control for GStreamer elements
renderproto RenderProto - Render extension headers
systemd systemd - systemd System and Service Manager
xcb-present XCB Present - XCB Present Extension
gdk-2.0 GDK - GTK+ Drawing Kit (x11 target)
gstreamer-dataprotocol-0.10 GStreamer data protocol library - Data protocol for plug-ins
gnome-icon-theme-symbolic gnome-icon-theme-symbolic - A collection of symbolic icons used as the basis for GNOME themes
libavfilter libavfilter - FFmpeg audio/video filtering library
libsystemd systemd - systemd Library
gnome-keybindings gnome-keybindings - Keybindings configuration for GNOME applications
glesv2 glesv2 - Mesa OpenGL ES 2.0 library
libdvbv5 libdvbv5 - DVBv5 utility library
xcursor Xcursor - X Cursor Library
libavcodec libavcodec - FFmpeg codec library
xi Xi - X Input Extension Library
xrandr Xrandr - X RandR Library
mysqlclient mysqlclient - MySQL client library
cairo-pdf cairo-pdf - PDF surface backend for cairo graphics library
egl egl - Mesa EGL library
xcb-sync XCB Sync - XCB Sync Extension
python Python - Python library
libraw1394 libraw1394 - Interface library for the Linux IEEE1394 drivers.
xcomposite Xcomposite - X Composite Extension Library
expat expat - expat XML parser
xcb-xv XCB Xv - XCB Xv Extension
xcb-shm XCB Shm - XCB Shm Extension
x11-xcb X11 XCB - X Library XCB interface
libxml-2.0 libXML - libXML library version2.
graphite2 Graphite2 - Font rendering engine for Complex Scripts
xcb-shape XCB Shape - XCB Shape Extension
dracut dracut - dracut
xt Xt - X Toolkit Library
libudev libudev - Library to access udev device information
pangocairo Pango Cairo - Cairo rendering support for Pango
gstreamer-rtp-0.10 GStreamer RTP Library - RTP base classes and helper functions
fixesproto FixesProto - X Fixes extension headers
gmodule-export-2.0 GModule - Dynamic module loader for GLib
cairo-glx cairo-glx - GLX functions for cairo graphics library
gbm gbm - Mesa gbm library
xcb-xkb XCB XKB - XCB Keyboard Extension (EXPERIMENTAL)
dri3proto DRI3Proto - DRI3 extension headers
dri dri - Direct Rendering Infrastructure
x11 X11 - X Library
cairo-xlib cairo-xlib - Xlib surface backend for cairo graphics library
xdamage Xdamage - X Damage Library
libsystemd-journal systemd - systemd Journal Utility Library - deprecated
xbitmaps X bitmaps - Bitmaps that are shared between X applications
damageproto DamageProto - Damage extension headers
xp Xp - X Print Library
kbproto KBProto - KB extension headers
xcb-xinput XCB XInput - XCB XInput Extension (EXPERIMENTAL)
xcb-dri2 XCB DRI2 - XCB DRI2 Extension
xcb-dri3 XCB DRI3 - XCB DRI3 Extension
pixman-1 Pixman - The pixman library (version 1)
xcb-xinerama XCB Xinerama - XCB Xinerama Extension
compositeproto CompositeExt - Composite extension headers
cairo-xcb-shm cairo-xcb-shm - XCB/SHM functions for cairo graphics library
gstreamer-0.10 GStreamer - Streaming media framework
xcb-xselinux XCB SELinux - XCB SELinux Extension
libdrm_amdgpu libdrm_amdgpu - Userspace interface to kernel DRM services for amdgpu
dri2proto DRI2Proto - DRI2 extension headers
xmuu Xmuu - Mini Xmu Library
libv4lconvert libv4lconvert - v4l format conversion library
xxf86vm Xxf86vm - XFree86 Video Mode Extension Library
xf86driproto XF86DRIProto - XF86DRI extension headers
icu-le icu-le - International Components for Unicode: Layout library
libpcre16 libpcre16 - PCRE - Perl compatible regular expressions C library with 16 bit character support
inputproto InputProto - Input extension headers
resourceproto ResourceProto - Resource extension headers
libdrm_radeon libdrm_radeon - Userspace interface to kernel DRM services for radeon
gobject-2.0 GObject - GLib Type, Object, Parameter and Signal Library
Magick++-7.Q16HDRI Magick++ - Magick++ - C++ API for ImageMagick (ABI Q16HDRI)
ImageMagick-7.Q16HDRI ImageMagick - ImageMagick - convert, edit, and compose images (ABI Q16HDRI)
libpng libpng - Loads and saves PNG files
xcb-dpms XCB DPMS - XCB DPMS Extension
cairo-fc cairo-fc - Fontconfig font backend for cairo graphics library
fontconfig Fontconfig - Font configuration and customization library
libva-egl libva-egl - Userspace Video Acceleration (VA) egl interface
MagickWand-7.Q16HDRI MagickWand - MagickWand - C API for ImageMagick (ABI Q16HDRI)
cairo cairo - Multi-platform 2D graphics library
python2 Python - Python library
icu-lx icu-lx - International Components for Unicode: Paragraph Layout library
gthread-2.0 GThread - Thread support for GLib
libpcreposix libpcreposix - PCREPosix - Posix compatible interface to libpcre
wayland-cursor Wayland Cursor - Wayland cursor helper library
xmu Xmu - Xmu Library
gstreamer-video-0.10 GStreamer Video Library - Video base classes and helper functions
xatracker xatracker - Xorg Gallium3D acceleration library
gstreamer-interfaces-0.10 GStreamer Interfaces Library - Interfaces for GStreamer elements
pangoxft Pango Xft - Xft font support for Pango
cairo-png cairo-png - PNG functions for cairo graphics library
cairo-ft cairo-ft - FreeType font backend for cairo graphics library
xcb-res XCB Res - XCB X-Resource Extension
wayland-scanner Wayland Scanner - Wayland scanner
xft Xft - X FreeType library
gstreamer-net-0.10 GStreamer networking library - Network-enabled GStreamer plug-ins and clocking
cairo-xlib-xrender cairo-xlib-xrender - Xlib Xrender surface backend for cairo graphics library
libdrm_intel libdrm_intel - Userspace interface to intel kernel DRM services
atk Atk - Accessibility Toolkit
xf86vidmodeproto XF86VidModeProto - XF86VidMode extension headers
gstreamer-floatcast-0.10 GStreamer Floatcast Library - Platform independent floating point macros
libva-x11 libva-x11 - Userspace Video Acceleration (VA) x11 interface
gstreamer-cdda-0.10 GStreamer CDDA Library - CDDA base classes
gtk+-x11-2.0 GTK+ - GTK+ Graphical UI Library (x11 target)
libva-drm libva-drm - Userspace Video Acceleration (VA) drm interface
glw glw - Mesa OpenGL widget library
icu-uc icu-uc - International Components for Unicode: Common and Data libraries
cairo-svg cairo-svg - SVG surface backend for cairo graphics library
gstreamer-app-0.10 GStreamer Application Library - Helper functions and base classes for application integration
printproto PrintProto - Print extension headers
wayland-egl wayland-egl - Mesa wayland-egl library
libdc1394-2 libdc1394 - 1394-based DC Control Library
sm SM - X Session Management Library
glu glu - Mesa OpenGL Utility library
check Check - A unit test framework for C
shared-mime-info shared-mime-info - Freedesktop common MIME database
harfbuzz harfbuzz - HarfBuzz text shaping library
cairo-gl cairo-gl - OpenGL surface backend for cairo graphics library
icu-i18n icu-i18n - International Components for Unicode: Internationalization library
xcb-render XCB Render - XCB Render Extension
recordproto RecordProto - Record extension headers
gstreamer-base-0.10 GStreamer base classes - Base classes for GStreamer elements
libpcre libpcre - PCRE - Perl compatible regular expressions C library with 8 bit character support
gdk-x11-2.0 GDK - GTK+ Drawing Kit (x11 target)
cairo-script cairo-script - script surface backend for cairo graphics library
libpcre32 libpcre32 - PCRE - Perl compatible regular expressions C library with 32 bit character support
gstreamer-rtsp-0.10 GStreamer RTSP Library - RTSP base classes and helper functions
xcmiscproto XCMiscProto - XCMisc extension headers
libkms libkms - Library that abstract aways the different mm interface for kernel drivers
libswresample libswresample - FFmpeg audio resampling library
cairo-tee cairo-tee - tee surface backend for cairo graphics library
freetype2 FreeType 2 - A free, high-quality, and portable font engine.
xcb-xf86dri XCB XFree86-DRI - XCB XFree86-DRI Extension
MagickCore MagickCore - MagickCore - C API for ImageMagick (ABI Q16HDRI)
xfixes Xfixes - X Fixes Library
gstreamer-fft-0.10 GStreamer FFT Library - FFT implementation
xcb-xfixes XCB XFixes - XCB XFixes Extension
libva-tpi libva-tpi - Userspace Video Acceleration (VA) 3rd party interface
xcb-screensaver XCB Screensaver - XCB Screensaver Extension
gtk+-2.0 GTK+ - GTK+ Graphical UI Library (x11 target)
gail Gail - GNOME Accessibility Implementation Library
evieproto EvIEExt - EvIE extension headers
libva-wayland libva-wayland - Userspace Video Acceleration (VA) wayland interface
xcb-glx XCB GLX - XCB GLX Extension
libsystemd-login systemd - systemd Login Utility Library - deprecated
scrnsaverproto ScrnSaverProto - ScrnSaver extension headers
udev udev - udev