define flags in header files or cpp files which invoke the flags

define flags with initial values

 DEFINE_bool(debug_mode, true, "if debug mode enabled");
 DEFINE_int32(port, 8899, "TCP port for server");
 DEFINE_int32(libbp_log_level, 4, "explanation");

in flag file, there should not be any spaces between flag and value, or the flag my be null

correct, FLAGS_my_flag will be a b c or "abc", pay attion to the spaces

 -my_flag=a b c
 -my_flag="abc"

<font color=#ff0000>wrong</font>, FLAGS_my_flag will be empty (nothing)

 -my_flag = abcded

1. with default flagfile

   the following code must be invoked in the your code fisrt

    google::SetCommandLineOption("flagfile", "default_flag_file_path")
   

2. with specific flagfile

    your_prog_with_gflags -flagfile 'flagfile_path'
   

3. with command line

    your_prog_with_gflags -my_flag1 value1 -my_flag2 value2
   

parse sequence, set default flagfile first, then parse the command line

flagfile is the reserved word of gflags, which defines which file to find the flags

 if (is_file_existed("list.conf") {
     google::SetCommandLineOption("flagfile", "list.conf");
 }
 google::ParseCommandLineFlags(&argc, &argv, true);

the above code will do the the following:

1. try to assign the flags by reading default flagfile list.conf
2. try to assign the flags by parsing the command line, values previously defined in flagfile will be override

Note that the flagfile can be define again in command line, which will make gflags to read the specific flagfile, flag defined in flagfile can always be override by command line

enjoy!

references

http://google-gflags.googlecode.com/svn/trunk/doc/gflags.html