Search Order

When environment variables and command-line options are used together the compiler searches the directories in the following order:

• Command-line options '-I' and '-L',from left to right.
• Directories specified by environment variables,such as C_INCLUDE_PATH and LIBRARY_PATH.
• Default system directories.
  Note:In day-to-day usage,directories are usually added to the search paths with the options '-I' and '-L'.

Creating a Library with ar

The GNU archiver ar combines a collection of objects files into a single archive file,also know as a library.An archive file is simply a convenient way of distributing a large number of related object files together.

• You can use the following command to create a static library:

$ ar cr libNAME.a file1.o file2.o ... filen.o

• The archiver ar also provides a "table of contents" option 't' to list the object files in an existing library.

$ ar t libNAME.a

EX：

main.c
mylib.h
func1.c
func2.c
使用 gcc -Wall * -c生成目标文件
目录
使用ar cr创建一个自己的库文件：
libadd.a

第三种方法，使用默认库：

使用库文件编译程序，生成可执行文件：

add

注意文件的编译顺序：

第一种方法：

-L

第二种方法（通过环境变量）：

LIBRARY_PATH

注：添加：$LIBRARY_PATH是防止变量原有的的内容被冲掉，表示最佳环境变量
2020.11.18