我需要从 INI 文件加载这些值并使用 C++ Boost 库在应用程序中打印它们。这些部分具有重复的名称。我被限制只能使用 C++ Boost 库。
numColors = 4
boardSize = 11
numSnails = 2
[initialization]
id = 0
row = 3
col = 4
orientation = 0
[initialization]
id = 1
row = 5
col = 0
orientation = 1
[color]
id = 0
nextColor = 1
deltaOrientation = +2
[color]
id = 1
nextColor = 2
deltaOrientation = +1
[color]
id = 2
nextColor = 3
deltaOrientation = -2
[color]
id = 3
nextColor = 0
deltaOrientation = -1
答案 0 :(得分:2)
我认为对于一个随机的路人来说,the Boost Spirit answer 可能看起来很复杂/矫枉过正。
我想再试一次,因为现在是 2021 年,无论是使用 C++17,我们都可以仅使用标准库来完成合理的工作。
事实证明,还有很多工作要做。 Qi 实现需要 86 行代码,但标准库实现需要 136 行。此外,调试/编写花了我更长的时间(几个小时)。特别是很难将 '='
, '['
, ']'
作为带有 std::istream&
的标记边界。我使用了这个答案中的 ctype
方面方法:How do I iterate over cin line by line in C++?
我确实在 DebugPeeker
(20 行)中留了下来,所以您或许可以自己理解。
顶级解析函数看起来很正常,并显示了我想要实现的目标:自然的 std::istream
提取:
static Ast::File std_parse_game(std::string_view input) {
std::istringstream iss{std::string(input)};
using namespace Helpers;
if (Ast::File parsed; iss >> parsed)
return parsed;
throw std::runtime_error("Unable to parse game");
}
其余的都在命名空间 Helpers
中:
static inline std::istream& operator>>(std::istream& is, Ast::File& v) {
for (section s; is >> s;) {
if (s.name == "parameters")
is >> v.parameters;
else if (s.name == "initialization")
is >> v.initializations.emplace_back();
else if (s.name == "color")
is >> v.colors.emplace_back();
else
is.setstate(std::ios::failbit);
}
if (is.eof())
is.clear();
return is;
}
到目前为止,这是一个很好的回报。不同的部分类型是相似的:
static inline std::istream& operator>>(std::istream& is, Ast::Parameters& v) {
return is
>> entry{"numColors", v.numColors}
>> entry{"boardSize", v.boardSize}
>> entry{"numSnails", v.numSnails};
}
static inline std::istream& operator>>(std::istream& is, Ast::Initialization& v) {
return is
>> entry{"id", v.id}
>> entry{"row", v.row}
>> entry{"col", v.col}
>> entry{"orientation", v.orientation};
}
static inline std::istream& operator>>(std::istream& is, Ast::Color& v) {
return is
>> entry{"id", v.id}
>> entry{"nextColor", v.nextColor}
>> entry{"deltaOrientation", v.deltaOrientation};
}
现在,如果一切都像这样一帆风顺,我不会推荐精神。现在我们进入条件解析。
entry{"name", value}
公式使用“操纵器类型”:
template <typename T> struct entry {
entry(std::string name, T& into) : _name(name), _into(into) {}
std::string _name;
T& _into;
friend std::istream& operator>>(std::istream& is, entry e) {
return is >> expect{e._name} >> expect{'='} >> e._into;
}
};
同样,部分使用 expect
和 token
:
struct section {
std::string name;
friend std::istream& operator>>(std::istream& is, section& s) {
if (is >> expect('['))
return is >> token{s.name} >> expect{']'};
return is;
}
};
条件对于能够在不将流置于硬失败模式的情况下检测到 EOF 很重要 (is.bad()
!= is.fail()
)。
expect
建立在 token
之上:
template <typename T> struct expect {
expect(T expected) : _expected(expected) {}
T _expected;
friend std::istream& operator>>(std::istream& is, expect const& e) {
if (T actual; is >> token{actual})
if (actual != e._expected)
is.setstate(std::ios::failbit);
return is;
}
};
您会注意到错误信息少得多。我们只是让
流 fail()
,以防未找到预期的令牌。
这就是真正复杂的地方。我不想解析字符
特点。但是使用 std::string
读取 operator>>
只会停止
空格,意味着节名称会“吃掉”括号:parameters]
而不是 parameters
,如果没有,键可能会吃掉 =
字符
分隔空间。
在上面链接的答案中,我们学习了如何建立自己的角色 分类区域设置方面:
// make sure =,[,] break tokens
struct mytoken_ctype : std::ctype<char> {
static auto const* get_table() {
static std::vector rc(table_size, std::ctype_base::mask());
rc[' '] = rc['\f'] = rc['\v'] = rc['\t'] = rc['\r'] = rc['\n'] =
std::ctype_base::space;
// crucial for us:
rc['='] = rc['['] = rc[']'] = std::ctype_base::space;
return rc.data();
}
mytoken_ctype() : std::ctype<char>(get_table()) {}
};
然后我们需要使用它,但前提是我们解析 std::string
标记。那
方式,如果我们 expect('=')
它不会跳过 '='
因为我们的方面称它为空白...
template <typename T> struct token {
token(T& into) : _into(into) {}
T& _into;
friend std::istream& operator>>(std::istream& is, token const& t) {
std::locale loc = is.getloc();
if constexpr (std::is_same_v<std::decay_t<T>, std::string>) {
loc = is.imbue(std::locale(std::locale(), new mytoken_ctype()));
}
try { is >> t._into; is.imbue(loc); }
catch (...) { is.imbue(loc); throw; }
return is;
}
};
我尽量保持简洁。如果我使用了正确的格式,我们会 还有更多的代码行:)
我使用了相同的 Ast 类型,因此测试两种实现和 比较结果是否相等。
<块引用>注意:
libfmt
以方便输出operator==
#include <boost/spirit/home/qi.hpp>
#include <boost/fusion/include/io.hpp>
#include <fstream>
#include <sstream>
#include <iomanip>
#include <fmt/ranges.h>
#include <fmt/ostream.h>
namespace qi = boost::spirit::qi;
namespace Ast {
using Id = unsigned;
using Size = uint16_t; // avoiding char types for easy debug/output
using Coord = Size;
using ColorNumber = Size;
using Orientation = Size;
using Delta = signed;
struct Parameters {
Size numColors{}, boardSize{}, numSnails{};
bool operator==(Parameters const&) const = default;
};
struct Initialization {
Id id;
Coord row;
Coord col;
Orientation orientation;
bool operator==(Initialization const&) const = default;
};
struct Color {
Id id;
ColorNumber nextColor;
Delta deltaOrientation;
bool operator==(Color const&) const = default;
};
struct File {
Parameters parameters;
std::vector<Initialization> initializations;
std::vector<Color> colors;
bool operator==(File const&) const = default;
};
using boost::fusion::operator<<;
template <typename T>
static inline std::ostream& operator<<(std::ostream& os, std::vector<T> const& v) {
return os << fmt::format("vector<{}>{}",
boost::core::demangle(typeid(T).name()), v);
}
} // namespace Ast
BOOST_FUSION_ADAPT_STRUCT(Ast::Parameters, numColors, boardSize, numSnails)
BOOST_FUSION_ADAPT_STRUCT(Ast::Initialization, id, row, col, orientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::Color, id, nextColor, deltaOrientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::File, parameters, initializations, colors)
template <typename It>
struct GameParser : qi::grammar<It, Ast::File()> {
GameParser() : GameParser::base_type(start) {
using namespace qi;
start = skip(blank)[file];
auto section = [](const std::string& name) {
return copy('[' >> lexeme[lit(name)] >> ']' >> (+eol | eoi));
};
auto required = [](const std::string& name, auto value) {
return copy(lexeme[eps > lit(name)] > '=' > value >
(+eol | eoi));
};
file = parameters >
*initialization >
*color >
eoi; // must reach end of input
parameters = section("parameters") >
required("numColors", _size) >
required("boardSize", _size) >
required("numSnails", _size);
initialization = section("initialization") >
required("id", _id) >
required("row", _coord) >
required("col", _coord) >
required("orientation", _orientation);
color = section("color") >
required("id", _id) >
required("nextColor", _colorNumber) >
required("deltaOrientation", _delta);
BOOST_SPIRIT_DEBUG_NODES((file)(parameters)(initialization)(color))
}
private:
using Skipper = qi::blank_type;
qi::rule<It, Ast::File()> start;
qi::rule<It, Ast::File(), Skipper> file;
// sections
qi::rule<It, Ast::Parameters(), Skipper> parameters;
qi::rule<It, Ast::Initialization(), Skipper> initialization;
qi::rule<It, Ast::Color(), Skipper> color;
// value types
qi::uint_parser<Ast::Id> _id;
qi::uint_parser<Ast::Size> _size;
qi::uint_parser<Ast::Coord> _coord;
qi::uint_parser<Ast::ColorNumber> _colorNumber;
qi::uint_parser<Ast::Orientation> _orientation;
qi::int_parser<Ast::Delta> _delta;
};
static Ast::File qi_parse_game(std::string_view input) {
using SVI = std::string_view::const_iterator;
static const GameParser<SVI> parser{};
try {
Ast::File parsed;
if (qi::parse(input.begin(), input.end(), parser, parsed)) {
return parsed;
}
throw std::runtime_error("Unable to parse game");
} catch (qi::expectation_failure<SVI> const& ef) {
std::ostringstream oss;
auto where = ef.first - input.begin();
auto sol = 1 + input.find_last_of("\r\n", where);
auto lineno = 1 + std::count(input.begin(), input.begin() + sol, '\n');
auto col = 1 + where - sol;
auto llen = input.substr(sol).find_first_of("\r\n");
oss << "input.txt:" << lineno << ":" << col << " Expected: " << ef.what_ << "\n"
<< " note: " << input.substr(sol, llen) << "\n"
<< " note:" << std::setw(col) << "" << "^--- here";
throw std::runtime_error(oss.str());
}
}
namespace Helpers {
struct DebugPeeker {
DebugPeeker(std::istream& is, int line) : is(is), line(line) { dopeek(); }
~DebugPeeker() { dopeek(); }
private:
std::istream& is;
int line;
void dopeek() const {
std::char_traits<char> t;
auto ch = is.peek();
std::cerr << "DEBUG " << line << " Peek: ";
if (std::isgraph(ch))
std::cerr << "'" << t.to_char_type(ch) << "'";
else
std::cerr << "<" << ch << ">";
std::cerr << " " << std::boolalpha << is.good() << "\n";
}
};
#define DEBUG_PEEK(is) // Peeker _peek##__LINE__(is, __LINE__);
// make sure =,[,] break tokens
struct mytoken_ctype : std::ctype<char> {
static auto const* get_table() {
static std::vector rc(table_size, std::ctype_base::mask());
rc[' '] = rc['\f'] = rc['\v'] = rc['\t'] = rc['\r'] = rc['\n'] =
std::ctype_base::space;
// crucial for us:
rc['='] = rc['['] = rc[']'] = std::ctype_base::space;
return rc.data();
}
mytoken_ctype() : std::ctype<char>(get_table()) {}
};
template <typename T> struct token {
token(T& into) : _into(into) {}
T& _into;
friend std::istream& operator>>(std::istream& is, token const& t) {
DEBUG_PEEK(is);
std::locale loc = is.getloc();
if constexpr (std::is_same_v<std::decay_t<T>, std::string>) {
loc = is.imbue(std::locale(std::locale(), new mytoken_ctype()));
}
try { is >> t._into; is.imbue(loc); }
catch (...) { is.imbue(loc); throw; }
return is;
}
};
template <typename T> struct expect {
expect(T expected) : _expected(expected) {}
T _expected;
friend std::istream& operator>>(std::istream& is, expect const& e) {
DEBUG_PEEK(is);
if (T actual; is >> token{actual})
if (actual != e._expected)
is.setstate(std::ios::failbit);
return is;
}
};
template <typename T> struct entry {
entry(std::string name, T& into) : _name(name), _into(into) {}
std::string _name;
T& _into;
friend std::istream& operator>>(std::istream& is, entry e) {
DEBUG_PEEK(is);
return is >> expect{e._name} >> expect{'='} >> e._into;
}
};
struct section {
std::string name;
friend std::istream& operator>>(std::istream& is, section& s) {
DEBUG_PEEK(is);
if (is >> expect('['))
return is >> token{s.name} >> expect{']'};
return is;
}
};
static inline std::istream& operator>>(std::istream& is, Ast::Parameters& v) {
DEBUG_PEEK(is);
return is
>> entry{"numColors", v.numColors}
>> entry{"boardSize", v.boardSize}
>> entry{"numSnails", v.numSnails};
}
static inline std::istream& operator>>(std::istream& is, Ast::Initialization& v) {
DEBUG_PEEK(is);
return is
>> entry{"id", v.id}
>> entry{"row", v.row}
>> entry{"col", v.col}
>> entry{"orientation", v.orientation};
}
static inline std::istream& operator>>(std::istream& is, Ast::Color& v) {
DEBUG_PEEK(is);
return is
>> entry{"id", v.id}
>> entry{"nextColor", v.nextColor}
>> entry{"deltaOrientation", v.deltaOrientation};
}
static inline std::istream& operator>>(std::istream& is, Ast::File& v) {
DEBUG_PEEK(is);
for (section s; is >> s;) {
if (s.name == "parameters")
is >> v.parameters;
else if (s.name == "initialization")
is >> v.initializations.emplace_back();
else if (s.name == "color")
is >> v.colors.emplace_back();
else
is.setstate(std::ios::failbit);
}
if (is.eof())
is.clear();
return is;
}
}
static Ast::File std_parse_game(std::string_view input) {
std::istringstream iss{std::string(input)};
using namespace Helpers;
if (Ast::File parsed; iss >> parsed)
return parsed;
throw std::runtime_error("Unable to parse game");
}
std::string read_file(const std::string& name) {
std::ifstream ifs(name);
return std::string(std::istreambuf_iterator<char>(ifs), {});
}
int main() {
std::string const game_save = read_file("input.txt");
Ast::File g1, g2;
try {
std::cout << "Qi: " << (g1 = qi_parse_game(game_save)) << "\n";
} catch (std::exception const& e) { std::cerr << e.what() << "\n"; }
try {
std::cout << "std: " << (g2 = std_parse_game(game_save)) << "\n";
} catch (std::exception const& e) { std::cerr << e.what() << "\n"; }
std::cout << "Equal: " << std::boolalpha << (g1 == g2) << "\n";
}
令我欣慰的是,解析器对数据达成了一致:
Qi: ((4 11 2)
vector<Ast::Initialization>{(0 3 4 0), (1 5 0 1)}
vector<Ast::Color>{(0 1 2), (1 2 1), (2 3 -2), (3 0 -1)})
std: ((4 11 2)
vector<Ast::Initialization>{(0 3 4 0), (1 5 0 1)}
vector<Ast::Color>{(0 1 2), (1 2 1), (2 3 -2), (3 0 -1)})
Equal: true
虽然这个答案是“标准的”和“便携的”,但它有一些缺点。
例如,正确处理当然并不容易,它几乎没有调试选项或错误报告,它不会验证输入格式。例如。它仍然会阅读这个邪恶的烂摊子并接受它:
[parameters] numColors=999 boardSize=999 numSnails=999
[color] id=0 nextColor=1 deltaOrientation=+2 [color] id=1 nextColor=2
deltaOrientation=+1 [
initialization] id=1 row=5 col=0 orientation=1
[color] id=2 nextColor=3 deltaOrientation=-2
[parameters] numColors=4 boardSize=11 numSnails=2
[color] id=3 nextColor=0 deltaOrientation=-1
[initialization] id=0 row=3 col=4 orientation=0
如果您的输入格式不稳定并且是计算机编写的,我强烈建议您不要使用标准库方法,因为它会导致难以诊断的问题和糟糕的用户体验(不要让您的用户想要抛出由于“无法解析游戏数据”等无用的错误消息,他们的计算机离开了窗口。
否则,你可能会。一方面,编译速度会更快。
答案 1 :(得分:1)
简而言之,这根本不是 INI 格式。它只是非常松散地相似。哪个不错。
你没有具体说明很多,所以我会做一些假设。
为了简单起见,我将假设
非必要的扣除(可用于添加更多验证):
为了表示文件,我会:
namespace Ast {
struct Initialization {
unsigned id, row, col, orientation;
};
struct Color {
unsigned id, nextColor;
int deltaOrientation;
};
struct File {
unsigned numColors, boardSize, numSnails;
std::vector<Initialization> initializations;
std::vector<Color> colors;
};
}
这是我能想到的最简单的。
对 Boost Spirit 来说是一份不错的工作。如果我们将数据结构调整为融合序列:
BOOST_FUSION_ADAPT_STRUCT(Ast::Initialization, id, row, col, orientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::Color, id, nextColor, deltaOrientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::File, numColors, boardSize, numSnails,
initializations, colors)
我们基本上可以让解析器“自己写”:
template <typename It>
struct GameParser : qi::grammar<It, Ast::File()> {
GameParser() : GameParser::base_type(start) {
using namespace qi;
start = skip(blank)[file];
auto section = [](std::string name) {
return copy('[' >> lexeme[lit(name)] >> ']' >> (+eol | eoi));
};
auto required = [](std::string name) {
return copy(lexeme[eps > lit(name)] > '=' > auto_ >
(+eol | eoi));
};
file =
required("numColors") >
required("boardSize") >
required("numSnails") >
*initialization >
*color >
eoi; // must reach end of input
initialization = section("initialization") >
required("id") >
required("row") >
required("col") >
required("orientation");
color = section("color") >
required("id") >
required("nextColor") >
required("deltaOrientation");
BOOST_SPIRIT_DEBUG_NODES((file)(initialization)(color))
}
private:
using Skipper = qi::blank_type;
qi::rule<It, Ast::File()> start;
qi::rule<It, Ast::File(), Skipper> file;
qi::rule<It, Ast::Initialization(), Skipper> initialization;
qi::rule<It, Ast::Color(), Skipper> color;
};
由于我们做出了许多假设,我们在这个地方散布了期望点(operator>
序列,而不是 operator>>
)。这意味着我们会收到无效输入的“有用”错误消息,例如
Expected: nextColor
Expected: =
Expected: <eoi>
<块引用>
另请参阅下面的奖励部分,可以大大改善这一点
测试它,我们将首先读取文件,然后使用该解析器解析它:
std::string read_file(std::string name) {
std::ifstream ifs(name);
return std::string(std::istreambuf_iterator<char>(ifs), {});
}
static Ast::File parse_game(std::string_view input) {
using SVI = std::string_view::const_iterator;
static const GameParser<SVI> parser{};
try {
Ast::File parsed;
if (qi::parse(input.begin(), input.end(), parser, parsed)) {
return parsed;
}
throw std::runtime_error("Unable to parse game");
} catch (qi::expectation_failure<SVI> const& ef) {
std::ostringstream oss;
oss << "Expected: " << ef.what_;
throw std::runtime_error(oss.str());
}
}
很多可以改进,但现在它可以工作并解析您的输入:
int main() {
std::string game_save = read_file("input.txt");
Ast::File data = parse_game(game_save);
}
没有输出就意味着成功。
一些改进,而不是使用 auto_
为类型生成正确的解析器,我们可以明确:
namespace Ast {
using Id = unsigned;
using Size = uint8_t;
using Coord = Size;
using ColorNumber = Size;
using Orientation = Size;
using Delta = signed;
struct Initialization {
Id id;
Coord row;
Coord col;
Orientation orientation;
};
struct Color {
Id id;
ColorNumber nextColor;
Delta deltaOrientation;
};
struct File {
Size numColors{}, boardSize{}, numSnails{};
std::vector<Initialization> initializations;
std::vector<Color> colors;
};
} // namespace Ast
然后在解析器中定义类似的:
qi::uint_parser<Ast::Id> _id;
qi::uint_parser<Ast::Size> _size;
qi::uint_parser<Ast::Coord> _coord;
qi::uint_parser<Ast::ColorNumber> _colorNumber;
qi::uint_parser<Ast::Orientation> _orientation;
qi::int_parser<Ast::Delta> _delta;
然后我们使用例如:
initialization = section("initialization") >
required("id", _id) >
required("row", _coord) >
required("col", _coord) >
required("orientation", _orientation);
现在我们可以改进错误信息,例如:
input.txt:2:13 Expected: <unsigned-integer>
note: boardSize = (11)
note: ^--- here
或
input.txt:16:19 Expected: <alternative><eol><eoi>
note: nextColor = 1 deltaOrientation = +2
note: ^--- here
完整代码,Live On Coliru
//#define BOOST_SPIRIT_DEBUG
#include <boost/spirit/home/qi.hpp>
#include <fstream>
#include <sstream>
#include <iomanip>
namespace qi = boost::spirit::qi;
namespace Ast {
using Id = unsigned;
using Size = uint8_t;
using Coord = Size;
using ColorNumber = Size;
using Orientation = Size;
using Delta = signed;
struct Initialization {
Id id;
Coord row;
Coord col;
Orientation orientation;
};
struct Color {
Id id;
ColorNumber nextColor;
Delta deltaOrientation;
};
struct File {
Size numColors{}, boardSize{}, numSnails{};
std::vector<Initialization> initializations;
std::vector<Color> colors;
};
} // namespace Ast
BOOST_FUSION_ADAPT_STRUCT(Ast::Initialization, id, row, col, orientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::Color, id, nextColor, deltaOrientation)
BOOST_FUSION_ADAPT_STRUCT(Ast::File, numColors, boardSize, numSnails,
initializations, colors)
template <typename It>
struct GameParser : qi::grammar<It, Ast::File()> {
GameParser() : GameParser::base_type(start) {
using namespace qi;
start = skip(blank)[file];
auto section = [](const std::string& name) {
return copy('[' >> lexeme[lit(name)] >> ']' >> (+eol | eoi));
};
auto required = [](const std::string& name, auto value) {
return copy(lexeme[eps > lit(name)] > '=' > value >
(+eol | eoi));
};
file =
required("numColors", _size) >
required("boardSize", _size) >
required("numSnails", _size) >
*initialization >
*color >
eoi; // must reach end of input
initialization = section("initialization") >
required("id", _id) >
required("row", _coord) >
required("col", _coord) >
required("orientation", _orientation);
color = section("color") >
required("id", _id) >
required("nextColor", _colorNumber) >
required("deltaOrientation", _delta);
BOOST_SPIRIT_DEBUG_NODES((file)(initialization)(color))
}
private:
using Skipper = qi::blank_type;
qi::rule<It, Ast::File()> start;
qi::rule<It, Ast::File(), Skipper> file;
qi::rule<It, Ast::Initialization(), Skipper> initialization;
qi::rule<It, Ast::Color(), Skipper> color;
qi::uint_parser<Ast::Id> _id;
qi::uint_parser<Ast::Size> _size;
qi::uint_parser<Ast::Coord> _coord;
qi::uint_parser<Ast::ColorNumber> _colorNumber;
qi::uint_parser<Ast::Orientation> _orientation;
qi::int_parser<Ast::Delta> _delta;
};
std::string read_file(const std::string& name) {
std::ifstream ifs(name);
return std::string(std::istreambuf_iterator<char>(ifs), {});
}
static Ast::File parse_game(std::string_view input) {
using SVI = std::string_view::const_iterator;
static const GameParser<SVI> parser{};
try {
Ast::File parsed;
if (qi::parse(input.begin(), input.end(), parser, parsed)) {
return parsed;
}
throw std::runtime_error("Unable to parse game");
} catch (qi::expectation_failure<SVI> const& ef) {
std::ostringstream oss;
auto where = ef.first - input.begin();
auto sol = 1 + input.find_last_of("\r\n", where);
auto lineno = 1 + std::count(input.begin(), input.begin() + sol, '\n');
auto col = 1 + where - sol;
auto llen = input.substr(sol).find_first_of("\r\n");
oss << "input.txt:" << lineno << ":" << col << " Expected: " << ef.what_ << "\n"
<< " note: " << input.substr(sol, llen) << "\n"
<< " note:" << std::setw(col) << "" << "^--- here";
throw std::runtime_error(oss.str());
}
}
int main() {
std::string game_save = read_file("input.txt");
try {
Ast::File data = parse_game(game_save);
} catch (std::exception const& e) {
std::cerr << e.what() << "\n";
}
}
在此处查看各种故障模式和 BOOST_SPIRIT_DEBUG 输出: