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// Copyright (c) 2006, Google Inc.
// All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
// ---
// Author: Ray Sidney
// Revamped and reorganized by Craig Silverstein
// This is the file that should be included by any file which declares
// or defines a command line flag or wants to parse command line flags
// or print a program usage message (which will include information about
// flags). Executive summary, in the form of an example file:
// #include "foo.h" // foo.h has a line "DECLARE_int32(start);"
// #include "validators.h" // hypothetical file defining ValidateIsFile()
// DEFINE_int32(end, 1000, "The last record to read");
// DEFINE_string(filename, "my_file.txt", "The file to read");
// // Crash if the specified file does not exist.
// static bool dummy = RegisterFlagValidator(&FLAGS_filename,
// &ValidateIsFile);
// DECLARE_bool(verbose); // some other file has a DEFINE_bool(verbose, ...)
// void MyFunc() {
// if (FLAGS_verbose) printf("Records %d-%d\n", FLAGS_start, FLAGS_end);
// }
// Then, at the command-line:
// ./foo --noverbose --start=5 --end=100
// For more details, see
// doc/gflags.html
// --- A note about thread-safety:
// We describe many functions in this routine as being thread-hostile,
// thread-compatible, or thread-safe. Here are the meanings we use:
// thread-safe: it is safe for multiple threads to call this routine
// (or, when referring to a class, methods of this class)
// concurrently.
// thread-hostile: it is not safe for multiple threads to call this
// routine (or methods of this class) concurrently. In gflags,
// most thread-hostile routines are intended to be called early in,
// or even before, main() -- that is, before threads are spawned.
// thread-compatible: it is safe for multiple threads to read from
// this variable (when applied to variables), or to call const
// methods of this class (when applied to classes), as long as no
// other thread is writing to the variable or calling non-const
// methods of this class.
#include <string>
#include <vector>
// We care a lot about number of bits things take up. Unfortunately,
// systems define their bit-specific ints in a lot of different ways.
// We use our own way, and have a typedef to get there.
// Note: these commands below may look like "#if 1" or "#if 0", but
// that's because they were constructed that way at ./configure time.
// Look at to see how they're calculated (based on your config).
#if 1
#include <stdint.h> // the normal place uint16_t is defined
#if 1
#include <sys/types.h> // the normal place u_int16_t is defined
#if 1
#include <inttypes.h> // a third place for uint16_t or u_int16_t
namespace google {
#if 1 // the C99 format
typedef int32_t int32;
typedef uint32_t uint32;
typedef int64_t int64;
typedef uint64_t uint64;
#elif 1 // the BSD format
typedef int32_t int32;
typedef u_int32_t uint32;
typedef int64_t int64;
typedef u_int64_t uint64;
#elif 0 // the windows (vc7) format
typedef __int32 int32;
typedef unsigned __int32 uint32;
typedef __int64 int64;
typedef unsigned __int64 uint64;
#error Do not know how to define a 32-bit integer quantity on your system
// --------------------------------------------------------------------
// To actually define a flag in a file, use DEFINE_bool,
// DEFINE_string, etc. at the bottom of this file. You may also find
// it useful to register a validator with the flag. This ensures that
// when the flag is parsed from the commandline, or is later set via
// SetCommandLineOption, we call the validation function. It is _not_
// called when you assign the value to the flag directly using the = operator.
// The validation function should return true if the flag value is valid, and
// false otherwise. If the function returns false for the new setting of the
// flag, the flag will retain its current value. If it returns false for the
// default value, ParseCommandLineFlags() will die.
// This function is safe to call at global construct time (as in the
// example below).
// Example use:
// static bool ValidatePort(const char* flagname, int32 value) {
// if (value > 0 && value < 32768) // value is ok
// return true;
// printf("Invalid value for --%s: %d\n", flagname, (int)value);
// return false;
// }
// DEFINE_int32(port, 0, "What port to listen on");
// static bool dummy = RegisterFlagValidator(&FLAGS_port, &ValidatePort);
// Returns true if successfully registered, false if not (because the
// first argument doesn't point to a command-line flag, or because a
// validator is already registered for this flag).
bool RegisterFlagValidator(const bool* flag,
bool (*validate_fn)(const char*, bool));
bool RegisterFlagValidator(const int32* flag,
bool (*validate_fn)(const char*, int32));
bool RegisterFlagValidator(const int64* flag,
bool (*validate_fn)(const char*, int64));
bool RegisterFlagValidator(const uint64* flag,
bool (*validate_fn)(const char*, uint64));
bool RegisterFlagValidator(const double* flag,
bool (*validate_fn)(const char*, double));
bool RegisterFlagValidator(const std::string* flag,
bool (*validate_fn)(const char*, const std::string&));
// --------------------------------------------------------------------
// These methods are the best way to get access to info about the
// list of commandline flags. Note that these routines are pretty slow.
// GetAllFlags: mostly-complete info about the list, sorted by file.
// ShowUsageWithFlags: pretty-prints the list to stdout (what --help does)
// ShowUsageWithFlagsRestrict: limit to filenames with restrict as a substr
// In addition to accessing flags, you can also access argv[0] (the program
// name) and argv (the entire commandline), which we sock away a copy of.
// These variables are static, so you should only set them once.
struct CommandLineFlagInfo {
std::string name; // the name of the flag
std::string type; // the type of the flag: int32, etc
std::string description; // the "help text" associated with the flag
std::string current_value; // the current value, as a string
std::string default_value; // the default value, as a string
std::string filename; // 'cleaned' version of filename holding the flag
bool has_validator_fn; // true if RegisterFlagValidator called on flag
bool is_default; // true if the flag has the default value and
// has not been set explicitly from the cmdline
// or via SetCommandLineOption
// Using this inside of a validator is a recipe for a deadlock.
// TODO(wojtekm) Fix locking when validators are running, to make it safe to
// call validators during ParseAllFlags.
// Also make sure then to uncomment the corresponding unit test in
extern void GetAllFlags(std::vector<CommandLineFlagInfo>* OUTPUT);
// These two are actually defined in
extern void ShowUsageWithFlags(const char *argv0); // what --help does
extern void ShowUsageWithFlagsRestrict(const char *argv0, const char *restrict);
// Create a descriptive string for a flag.
// Goes to some trouble to make pretty line breaks.
extern std::string DescribeOneFlag(const CommandLineFlagInfo& flag);
// Thread-hostile; meant to be called before any threads are spawned.
extern void SetArgv(int argc, const char** argv);
// The following functions are thread-safe as long as SetArgv() is
// only called before any threads start.
extern const std::vector<std::string>& GetArgvs(); // all of argv as a vector
extern const char* GetArgv(); // all of argv as a string
extern const char* GetArgv0(); // only argv0
extern uint32 GetArgvSum(); // simple checksum of argv
extern const char* ProgramInvocationName(); // argv0, or "UNKNOWN" if not set
extern const char* ProgramInvocationShortName(); // basename(argv0)
// ProgramUsage() is thread-safe as long as SetUsageMessage() is only
// called before any threads start.
extern const char* ProgramUsage(); // string set by SetUsageMessage()
// --------------------------------------------------------------------
// Normally you access commandline flags by just saying "if (FLAGS_foo)"
// or whatever, and set them by calling "FLAGS_foo = bar" (or, more
// commonly, via the DEFINE_foo macro). But if you need a bit more
// control, we have programmatic ways to get/set the flags as well.
// These programmatic ways to access flags are thread-safe, but direct
// access is only thread-compatible.
// Return true iff the flagname was found.
// OUTPUT is set to the flag's value, or unchanged if we return false.
extern bool GetCommandLineOption(const char* name, std::string* OUTPUT);
// Return true iff the flagname was found. OUTPUT is set to the flag's
// CommandLineFlagInfo or unchanged if we return false.
extern bool GetCommandLineFlagInfo(const char* name,
CommandLineFlagInfo* OUTPUT);
// Return the CommandLineFlagInfo of the flagname. exit() if name not found.
// Example usage, to check if a flag's value is currently the default value:
// if (GetCommandLineFlagInfoOrDie("foo").is_default) ...
extern CommandLineFlagInfo GetCommandLineFlagInfoOrDie(const char* name);
enum FlagSettingMode {
// update the flag's value (can call this multiple times).
// update the flag's value, but *only if* it has not yet been updated
// with SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef".
// set the flag's default value to this. If the flag has not yet updated
// yet (via SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef")
// change the flag's current value to the new default value as well.
// Set a particular flag ("command line option"). Returns a string
// describing the new value that the option has been set to. The
// return value API is not well-specified, so basically just depend on
// it to be empty if the setting failed for some reason -- the name is
// not a valid flag name, or the value is not a valid value -- and
// non-empty else.
// SetCommandLineOption uses set_mode == SET_FLAGS_VALUE (the common case)
extern std::string SetCommandLineOption(const char* name, const char* value);
extern std::string SetCommandLineOptionWithMode(const char* name, const char* value,
FlagSettingMode set_mode);
// --------------------------------------------------------------------
// Saves the states (value, default value, whether the user has set
// the flag, registered validators, etc) of all flags, and restores
// them when the FlagSaver is destroyed. This is very useful in
// tests, say, when you want to let your tests change the flags, but
// make sure that they get reverted to the original states when your
// test is complete.
// Example usage:
// void TestFoo() {
// FlagSaver s1;
// FLAG_foo = false;
// FLAG_bar = "some value";
// // test happens here. You can return at any time
// // without worrying about restoring the FLAG values.
// }
// Note: This class is marked with __attribute__((unused)) because all the
// work is done in the constructor and destructor, so in the standard
// usage example above, the compiler would complain that it's an
// unused variable.
// This class is thread-safe.
class FlagSaver {
class FlagSaverImpl* impl_; // we use pimpl here to keep API steady
FlagSaver(const FlagSaver&); // no copying!
void operator=(const FlagSaver&);
} __attribute__ ((unused));
// --------------------------------------------------------------------
// Some deprecated or hopefully-soon-to-be-deprecated functions.
// This is often used for logging. TODO(csilvers): figure out a better way
extern std::string CommandlineFlagsIntoString();
// Usually where this is used, a FlagSaver should be used instead.
extern bool ReadFlagsFromString(const std::string& flagfilecontents,
const char* prog_name,
bool errors_are_fatal); // uses SET_FLAGS_VALUE
// These let you manually implement --flagfile functionality.
extern bool AppendFlagsIntoFile(const std::string& filename, const char* prog_name);
extern bool SaveCommandFlags(); // actually defined in !
extern bool ReadFromFlagsFile(const std::string& filename, const char* prog_name,
bool errors_are_fatal); // uses SET_FLAGS_VALUE
// --------------------------------------------------------------------
// Useful routines for initializing flags from the environment.
// In each case, if 'varname' does not exist in the environment
// return defval. If 'varname' does exist but is not valid
// (e.g., not a number for an int32 flag), abort with an error.
// Otherwise, return the value. NOTE: for booleans, for true use
// 't' or 'T' or 'true' or '1', for false 'f' or 'F' or 'false' or '0'.
extern bool BoolFromEnv(const char *varname, bool defval);
extern int32 Int32FromEnv(const char *varname, int32 defval);
extern int64 Int64FromEnv(const char *varname, int64 defval);
extern uint64 Uint64FromEnv(const char *varname, uint64 defval);
extern double DoubleFromEnv(const char *varname, double defval);
extern const char *StringFromEnv(const char *varname, const char *defval);
// --------------------------------------------------------------------
// The next two functions parse commandlineflags from main():
// Set the "usage" message for this program. For example:
// string usage("This program does nothing. Sample usage:\n");
// usage += argv[0] + " <uselessarg1> <uselessarg2>";
// SetUsageMessage(usage);
// Do not include commandline flags in the usage: we do that for you!
// Thread-hostile; meant to be called before any threads are spawned.
extern void SetUsageMessage(const std::string& usage);
// Looks for flags in argv and parses them. Rearranges argv to put
// flags first, or removes them entirely if remove_flags is true.
// If a flag is defined more than once in the command line or flag
// file, the last definition is used. Returns the index (into argv)
// of the first non-flag argument.
// See top-of-file for more details on this function.
#ifndef SWIG // In swig, use ParseCommandLineFlagsScript() instead.
extern uint32 ParseCommandLineFlags(int *argc, char*** argv,
bool remove_flags);
// Calls to ParseCommandLineNonHelpFlags and then to
// HandleCommandLineHelpFlags can be used instead of a call to
// ParseCommandLineFlags during initialization, in order to allow for
// changing default values for some FLAGS (via
// e.g. SetCommandLineOptionWithMode calls) between the time of
// command line parsing and the time of dumping help information for
// the flags as a result of command line parsing. If a flag is
// defined more than once in the command line or flag file, the last
// definition is used. Returns the index (into argv) of the first
// non-flag argument. (If remove_flags is true, will always return 1.)
extern uint32 ParseCommandLineNonHelpFlags(int *argc, char*** argv,
bool remove_flags);
// This is actually defined in
// This function is misnamed (it also handles --version, etc.), but
// it's too late to change that now. :-(
extern void HandleCommandLineHelpFlags(); // in
// Allow command line reparsing. Disables the error normally
// generated when an unknown flag is found, since it may be found in a
// later parse. Thread-hostile; meant to be called before any threads
// are spawned.
extern void AllowCommandLineReparsing();
// Reparse the flags that have not yet been recognized. Only flags
// registered since the last parse will be recognized. Any flag value
// must be provided as part of the argument using "=", not as a
// separate command line argument that follows the flag argument.
// Intended for handling flags from dynamically loaded libraries,
// since their flags are not registered until they are loaded.
// Returns the index (into the original argv) of the first non-flag
// argument. (If remove_flags is true, will always return 1.)
extern uint32 ReparseCommandLineNonHelpFlags();
// Clean up memory allocated by flags. This is only needed to reduce
// the quantity of "potentially leaked" reports emitted by memory
// debugging tools such as valgrind. It is not required for normal
// operation, or for the perftools heap-checker. It must only be called
// when the process is about to exit, and all threads that might
// access flags are quiescent. Referencing flags after this is called
// will have unexpected consequences. This is not safe to run when
// multiple threads might be running: the function is thread-hostile.
extern void ShutDownCommandLineFlags();
// --------------------------------------------------------------------
// Now come the command line flag declaration/definition macros that
// will actually be used. They're kind of hairy. A major reason
// for this is initialization: we want people to be able to access
// variables in global constructors and have that not crash, even if
// their global constructor runs before the global constructor here.
// (Obviously, we can't guarantee the flags will have the correct
// default value in that case, but at least accessing them is safe.)
// The only way to do that is have flags point to a static buffer.
// So we make one, using a union to ensure proper alignment, and
// then use placement-new to actually set up the flag with the
// correct default value. In the same vein, we have to worry about
// flag access in global destructors, so FlagRegisterer has to be
// careful never to destroy the flag-values it constructs.
// Note that when we define a flag variable FLAGS_<name>, we also
// preemptively define a junk variable, FLAGS_no<name>. This is to
// cause a link-time error if someone tries to define 2 flags with
// names like "logging" and "nologging". We do this because a bool
// flag FLAG can be set from the command line to true with a "-FLAG"
// argument, and to false with a "-noFLAG" argument, and so this can
// potentially avert confusion.
// We also put flags into their own namespace. It is purposefully
// named in an opaque way that people should have trouble typing
// directly. The idea is that DEFINE puts the flag in the weird
// namespace, and DECLARE imports the flag from there into the current
// namespace. The net result is to force people to use DECLARE to get
// access to a flag, rather than saying "extern bool FLAGS_whatever;"
// or some such instead. We want this so we can put extra
// functionality (like sanity-checking) in DECLARE if we want, and
// make sure it is picked up everywhere.
// We also put the type of the variable in the namespace, so that
// people can't DECLARE_int32 something that they DEFINE_bool'd
// elsewhere.
class FlagRegisterer {
FlagRegisterer(const char* name, const char* type,
const char* help, const char* filename,
void* current_storage, void* defvalue_storage);
extern bool FlagsTypeWarn(const char *name);
// If your application #defines STRIP_FLAG_HELP to a non-zero value
// before #including this file, we remove the help message from the
// binary file. This can reduce the size of the resulting binary
// somewhat, and may also be useful for security reasons.
extern const char kStrippedFlagHelp[];
#ifndef SWIG // In swig, ignore the main flag declarations
// Need this construct to avoid the 'defined but not used' warning.
#define MAYBE_STRIPPED_HELP(txt) (false ? (txt) : ::google::kStrippedFlagHelp)
#define MAYBE_STRIPPED_HELP(txt) txt
// Each command-line flag has two variables associated with it: one
// with the current value, and one with the default value. However,
// we have a third variable, which is where value is assigned; it's a
// constant. This guarantees that FLAG_##value is initialized at
// static initialization time (e.g. before program-start) rather than
// than global construction time (which is after program-start but
// before main), at least when 'value' is a compile-time constant. We
// use a small trick for the "default value" variable, and call it
// FLAGS_no<name>. This serves the second purpose of assuring a
// compile error if someone tries to define a flag named no<name>
// which is illegal (--foo and --nofoo both affect the "foo" flag).
#define DEFINE_VARIABLE(type, shorttype, name, value, help) \
namespace fL##shorttype { \
static const type FLAGS_nono##name = value; \
type FLAGS_##name = FLAGS_nono##name; \
type FLAGS_no##name = FLAGS_nono##name; \
static ::google::FlagRegisterer o_##name( \
#name, #type, MAYBE_STRIPPED_HELP(help), __FILE__, \
&FLAGS_##name, &FLAGS_no##name); \
} \
using fL##shorttype::FLAGS_##name
#define DECLARE_VARIABLE(type, shorttype, name) \
namespace fL##shorttype { \
extern type FLAGS_##name; \
} \
using fL##shorttype::FLAGS_##name
// For DEFINE_bool, we want to do the extra check that the passed-in
// value is actually a bool, and not a string or something that can be
// coerced to a bool. These declarations (no definition needed!) will
// help us do that, and never evaluate From, which is important.
// We'll use 'sizeof(IsBool(val))' to distinguish. This code requires
// that the compiler have different sizes for bool & double. Since
// this is not guaranteed by the standard, we check it with a
// compile-time assert (msg[-1] will give a compile-time error).
namespace fLB {
struct CompileAssert {};
typedef CompileAssert expected_sizeof_double_neq_sizeof_bool[
(sizeof(double) != sizeof(bool)) ? 1 : -1];
template<typename From> double IsBoolFlag(const From& from);
bool IsBoolFlag(bool from);
} // namespace fLB
#define DECLARE_bool(name) DECLARE_VARIABLE(bool, B, name)
#define DEFINE_bool(name, val, txt) \
namespace fLB { \
typedef ::fLB::CompileAssert FLAG_##name##_value_is_not_a_bool[ \
(sizeof(::fLB::IsBoolFlag(val)) != sizeof(double)) ? 1 : -1]; \
} \
DEFINE_VARIABLE(bool, B, name, val, txt)
#define DECLARE_int32(name) DECLARE_VARIABLE(::google::int32, I, name)
#define DEFINE_int32(name,val,txt) DEFINE_VARIABLE(::google::int32, I, name, val, txt)
#define DECLARE_int64(name) DECLARE_VARIABLE(::google::int64, I64, name)
#define DEFINE_int64(name,val,txt) DEFINE_VARIABLE(::google::int64, I64, name, val, txt)
#define DECLARE_uint64(name) DECLARE_VARIABLE(::google::uint64, U64, name)
#define DEFINE_uint64(name,val,txt) DEFINE_VARIABLE(::google::uint64, U64, name, val, txt)
#define DECLARE_double(name) DECLARE_VARIABLE(double, D, name)
#define DEFINE_double(name, val, txt) DEFINE_VARIABLE(double, D, name, val, txt)
// Strings are trickier, because they're not a POD, so we can't
// construct them at static-initialization time (instead they get
// constructed at global-constructor time, which is much later). To
// try to avoid crashes in that case, we use a char buffer to store
// the string, which we can static-initialize, and then placement-new
// into it later. It's not perfect, but the best we can do.
namespace fLS {
// The meaning of "string" might be different between now and when the
// macros below get invoked (e.g., if someone is experimenting with
// other string implementations that get defined after this file is
// included). Save the current meaning now and use it in the macros.
typedef std::string clstring;
inline clstring* dont_pass0toDEFINE_string(char *stringspot,
const char *value) {
return new(stringspot) clstring(value);
inline clstring* dont_pass0toDEFINE_string(char *stringspot,
const clstring &value) {
return new(stringspot) clstring(value);
inline clstring* dont_pass0toDEFINE_string(char *stringspot,
int value);
} // namespace fLS
#define DECLARE_string(name) namespace fLS { extern ::fLS::clstring& FLAGS_##name; } \
using fLS::FLAGS_##name
// We need to define a var named FLAGS_no##name so people don't define
// --string and --nostring. And we need a temporary place to put val
// so we don't have to evaluate it twice. Two great needs that go
// great together!
// The weird 'using' + 'extern' inside the fLS namespace is to work around
// an unknown compiler bug/issue with the gcc 4.2.1 on SUSE 10. See
#define DEFINE_string(name, val, txt) \
namespace fLS { \
using ::fLS::clstring; \
static union { void* align; char s[sizeof(clstring)]; } s_##name[2]; \
clstring* const FLAGS_no##name = ::fLS:: \
dont_pass0toDEFINE_string(s_##name[0].s, \
val); \
static ::google::FlagRegisterer o_##name( \
#name, "string", MAYBE_STRIPPED_HELP(txt), __FILE__, \
s_##name[0].s, new (s_##name[1].s) clstring(*FLAGS_no##name)); \
extern clstring& FLAGS_##name; \
using fLS::FLAGS_##name; \
clstring& FLAGS_##name = *FLAGS_no##name; \
} \
using fLS::FLAGS_##name
#endif // SWIG
#endif // GOOGLE_GFLAGS_H_