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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Provides a simple class, |CommandLine|, for dealing with command lines (and
// flags and positional arguments).
// * Options (a.k.a. flags or switches) are all of the form "--name=<value>" (or
// "--name", but this is indistinguishable from "--name="), where <value> is a
// string. Not supported: "-name", "-n", "--name <value>", "-n <value>", etc.
// * Option order is preserved.
// * Option processing is stopped after the first positional argument[*]. Thus
// in the command line "my_program --foo bar --baz", only "--foo" is an option
// ("bar" and "--baz" are positional arguments).
// * Options can be looked up by name. If the same option occurs multiple times,
// convention is to use the last occurrence (and the provided look-up
// functions behave this way).
// * "--" may also be used to separate options from positional arguments. Thus
// in the command line "my_program --foo -- --bar", "--bar" is a positional
// argument.
// * |CommandLine|s store |argv[0]| and distinguish between not having |argv[0]|
// and |argv[0]| being empty.
// * Apart from being copyable and movable, |CommandLine|s are immutable.
// There are factory functions to turn raw arguments into |CommandLine|s, in
// accordance with the above rules. However, |CommandLine|s may be used more
// generically (with the user transforming arguments using different rules,
// e.g., accepting "-name" as an option), subject to certain limitations (e.g.,
// not being able to distinguish "no value" from "empty value").
// [*] This is somewhat annoying for users, but: a. it's standard Unix behavior
// for most command line parsers, b. it makes "my_program *" (etc.) safer (which
// mostly explains a.), c. it makes parsing "subcommands", like "my_program
// --flag_for_my_program subcommand --flag_for_subcommand" saner.
#include <cstddef>
#include <initializer_list>
#include <string>
#include <string_view>
#include <unordered_map>
#include <vector>
#include "flutter/fml/macros.h"
namespace fml {
// CommandLine -----------------------------------------------------------------
// Class that stores processed command lines ("argv[0]", options, and positional
// arguments) and provides access to them. For more details, see the file-level
// comment above. This class is thread-safe.
class CommandLine final {
class ConstructionHelper;
struct Option {
Option() {}
explicit Option(const std::string& name);
Option(const std::string& name, const std::string& value);
bool operator==(const Option& other) const {
return name == && value == other.value;
bool operator!=(const Option& other) const { return !operator==(other); }
std::string name;
std::string value;
// Default, copy, and move constructors (to be out-of-lined).
CommandLine(const CommandLine& from);
CommandLine(CommandLine&& from);
// Constructs a |CommandLine| from its "components". This is especially useful
// for creating a new |CommandLine| based on an existing |CommandLine| (e.g.,
// adding options or arguments).
explicit CommandLine(const std::string& argv0,
const std::vector<Option>& options,
const std::vector<std::string>& positional_args);
// Copy and move assignment (to be out-of-lined).
CommandLine& operator=(const CommandLine& from);
CommandLine& operator=(CommandLine&& from);
bool has_argv0() const { return has_argv0_; }
const std::string& argv0() const { return argv0_; }
const std::vector<Option>& options() const { return options_; }
const std::vector<std::string>& positional_args() const {
return positional_args_;
bool operator==(const CommandLine& other) const {
// No need to compare |option_index_|.
return has_argv0_ == other.has_argv0_ && argv0_ == other.argv0_ &&
options_ == other.options_ &&
positional_args_ == other.positional_args_;
bool operator!=(const CommandLine& other) const { return !operator==(other); }
// Returns true if this command line has the option |name| (and if |index| is
// non-null, sets |*index| to the index of the *last* occurrence of the given
// option in |options()|) and false if not.
bool HasOption(std::string_view name, size_t* index = nullptr) const;
// Gets the value of the option |name|. Returns true (and sets |*value|) on
// success and false (leaving |*value| alone) on failure.
bool GetOptionValue(std::string_view name, std::string* value) const;
// Gets all values of the option |name|. Returns all values, which may be
// empty if the option is not specified.
std::vector<std::string_view> GetOptionValues(std::string_view name) const;
// Gets the value of the option |name|, with a default if the option is not
// specified. (Note: This doesn't return a const reference, since this would
// make the |default_value| argument inconvenient/dangerous.)
std::string GetOptionValueWithDefault(std::string_view name,
std::string_view default_value) const;
bool has_argv0_ = false;
// The following should all be empty if |has_argv0_| is false.
std::string argv0_;
std::vector<Option> options_;
std::vector<std::string> positional_args_;
// Maps option names to position in |options_|. If a given name occurs
// multiple times, the index will be to the *last* occurrence.
std::unordered_map<std::string, size_t> option_index_;
// Allow copy and assignment.
// Factory functions (etc.) ----------------------------------------------------
namespace internal {
// Helper class for building command lines (finding options, etc.) from raw
// arguments.
class CommandLineBuilder final {
// Processes an additional argument in the command line. Returns true if |arg|
// is the *first* positional argument.
bool ProcessArg(const std::string& arg);
// Builds a |CommandLine| from the arguments processed so far.
CommandLine Build() const;
bool has_argv0_ = false;
std::string argv0_;
std::vector<CommandLine::Option> options_;
std::vector<std::string> positional_args_;
// True if we've started processing positional arguments.
bool started_positional_args_ = false;
} // namespace internal
// The following factory functions create |CommandLine|s from raw arguments in
// accordance with the rules outlined at the top of this file. (Other ways of
// transforming raw arguments into options and positional arguments are
// possible.)
// Like |CommandLineFromIterators()| (see below), but sets
// |*first_positional_arg| to point to the first positional argument seen (or
// |last| if none are seen). This is useful for processing "subcommands".
template <typename InputIterator>
inline CommandLine CommandLineFromIteratorsFindFirstPositionalArg(
InputIterator first,
InputIterator last,
InputIterator* first_positional_arg) {
if (first_positional_arg)
*first_positional_arg = last;
internal::CommandLineBuilder builder;
for (auto it = first; it < last; ++it) {
if (builder.ProcessArg(*it)) {
if (first_positional_arg)
*first_positional_arg = it;
return builder.Build();
// Builds a |CommandLine| from first/last iterators (where |last| is really
// one-past-the-last, as usual) to |std::string|s or things that implicitly
// convert to |std::string|.
template <typename InputIterator>
inline CommandLine CommandLineFromIterators(InputIterator first,
InputIterator last) {
return CommandLineFromIteratorsFindFirstPositionalArg<InputIterator>(
first, last, nullptr);
// Builds a |CommandLine| from first/last iterators (where |last| is really
// one-past-the-last, as usual) to |std::string|s or things that implicitly
// convert to |std::string|, where argv[0] is provided separately.
template <typename InputIterator>
inline CommandLine CommandLineFromIteratorsWithArgv0(const std::string& argv0,
InputIterator first,
InputIterator last) {
internal::CommandLineBuilder builder;
for (auto it = first; it < last; ++it)
return builder.Build();
// Builds a |CommandLine| from the usual argc/argv.
inline CommandLine CommandLineFromArgcArgv(int argc, const char* const* argv) {
return CommandLineFromIterators(argv, argv + argc);
// Builds a |CommandLine| from an initializer list of |std::string|s or things
// that implicitly convert to |std::string|.
template <typename StringType>
inline CommandLine CommandLineFromInitializerList(
std::initializer_list<StringType> argv) {
return CommandLineFromIterators(argv.begin(), argv.end());
// This is the "opposite" of the above factory functions, transforming a
// |CommandLine| into a vector of argument strings according to the rules
// outlined at the top of this file.
std::vector<std::string> CommandLineToArgv(const CommandLine& command_line);
} // namespace fml