#include <gflags/gflags.h> DEFINE_string(message, "", "The message to print"); void print_message(); // in gflags_declare_flags.cc int main(int argc, char **argv) { GFLAGS_NAMESPACE::SetUsageMessage("Test compilation and use of gflags_declare.h"); GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true); print_message(); return 0; }