Gflags, the command-line flags library used within Google, differs from other libraries, such as getopt(), in that flag definitions can be scattered around the source code, and not just listed in one place such as main(). In practice, this means that a single source-code file will define and use flags that are meaningful to that file. Any application that links in that file will get the flags, and the gflags library will automatically handle that flag appropriately.