pkg-config

1. pkg-config 的使用说明可以参见:

2. 如查看本机的package list:
   # which pkg-list
   /usr/bin/pkg-config
  
   # pkg-config --list-all
   ......

3. pkg-config 从系统的库搜索路径中寻找 pkgconfig 文件夹里面的 *.pc 文件，读出里面的信息。

4. pkg-config搜索 ＊.pc 的规则是，遍历系统的所有链接库搜索路径。因此，一般情况下，*.pc 文件会和库文件装在同一个 prefix 目录下。

   比如，如果 DirectFB 装在 /usr/local/lib/ 下的话， 对应的 .pc 文件就被装在
/usr/local/lib/pkgconfig 下。

   # ls /usr/local/lib/pkgconfig
   direct.pc  directfb-internal.pc  directfb.pc  fusion.pc

5. .pc 文件里记载里库的版本，路径，使用库的编译器选项等信息。如：

　　# cat /usr/local/lib/pkgconfig/directfb.pc
-------------------------------------------------------------------------------
prefix=/usr/local
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Name: DirectFB
Description: Graphics and windowing library for the Linux frame buffer device
Version: 1.3.0
Requires: fusion direct
Libs: -L${libdir} -ldirectfb -lpthread
Libs.private: -L${libdir} -ldl -lz
Cflags: -D_REENTRANT -I${prefix}/include/directfb
-------------------------------------------------------------------------------

6. 如果所使用的库文件不在系统的库搜索路径的时候，可以通过变量PKG_CONFIG_PATH来指定路径：

   # PKG_CONFIG_PATH=/usr/local/lib/pkgconfig pkg-config --exists --print-errors directfb

7. DirectFB 1.3 使用 pkg-config来安装库文件。如果系统有几个 pkg-config 命令的时候（比如，交叉编译的时候），可以使用　PKG_CONFIG 选项指定　pkg-config路径。具体参看 ./configure --help

8. 常见错误:

   ......
   checking for pkg-config... /usr/bin/pkg-config
   checking pkg-config is at least version 0.9.0... yes
   checking for DIRECTFB... no
   configure: error: Requested 'directfb >= 1.2.0' but version of DirectFB is 1.0.1
   *** DirectFB 1.2.0 or newer is required. The latest version
   *** of DirectFB is available from
   make: *** No targets specified and no makefile found.  Stop.

   安装了两个不同版本的DirectFB，先找到了低版本的，报错~~~~

(config.log)
......
configure:4285: checking for pkg-config
configure:4303: found /usr/bin/pkg-config
configure:4315: result: /usr/bin/pkg-config
configure:4344: checking pkg-config is at least version 0.9.0
configure:4347: result: yes
configure:4358: checking for DIRECTFB
configure:4366: $PKG_CONFIG --exists --print-errors "directfb >= $VERSION"
Package directfb was not found in the pkg-config search path.
Perhaps you should add the directory containing `directfb.pc'
to the PKG_CONFIG_PATH environment variable
No package 'directfb' found
configure:4369: $? = 1
configure:4384: $PKG_CONFIG --exists --print-errors "directfb >= $VERSION"
Package directfb was not found in the pkg-config search path.
Perhaps you should add the directory containing `directfb.pc'
to the PKG_CONFIG_PATH environment variable
No package 'directfb' found
configure:4387: $? = 1
No package 'directfb' found
configure:4415: result: no
configure:4419: error: No package 'directfb' found
*** DirectFB 1.2.0 or newer is required. The latest version
*** of DirectFB is available from

没有找到 DirectFB　库，如果你安装了库pkg-config　没有找到的话，基本上就是:
  1) 安装的库不在它的搜索路径
　2) 没有安装 .pc 文件