006_wz_bbk_Make，外部库

Recompiling and Relinking

• In genaral,linking is a faster than compliation----in a large project with many source files,recompiling only those that have been modified can make a significant saving.
• The process of recompiling only the modified files in a project cna be antomated using GNU Make

Linking With External Libraries

• A library is a collection of precompiled object files which can be linked into programs.The most common use of libraries is to provide system function,such as the square root function sqrt found in the C math library.
• Libraries are typically stored in special archive files with the extension '.a',referred to as static libraries.They are created from object files with a separate tool,the GNU archiver ar,and used by the linker to resolve refernces to functions at compile-time.
• The standard system libraries are usually found in the directories '/usr/lib' and '/lib'.