Boost 属性 树指定允许值
Boost property tree specify allowed values
我想使用 boosts 属性 tree 来处理我的 c++ 应用程序的设置,因为它似乎在这种情况下被广泛使用。
我的问题:在 属性 树中更改值时(通过 xml 解析或手动),有没有办法预先指定键的允许值列表?
例如。如果我想做一个简单的 "Yes/No" 设置,我是否必须使用 if - 条件检查值,或者我可以以某种方式教我的树只接受两个值 "Yes" 和 "No"提前获取特定的键,以便它在出错时抛出异常。
您可以为此使用翻译器。一个不错的博客 post 我记得这里描述了这个以在 XML 支持的 属性 树中获取自定义日期格式解析:
让我们举个例子:
enum class YesNo { No, Yes };
在这种情况下,调用代码可能如下所示:
static YesNoTranslator trans;
int main() {
std::istringstream iss(R"(
<?xml version="1.0"?>
<demo>
<positive>Yes</positive>
<negative>No</negative>
<invalid>Bogus</invalid>
</demo>
)");
ptree pt;
read_xml(iss, pt);
for (auto&& field : { "demo.positive", "demo.negative", "demo.invalid" })
{
try {
std::cout << "With 'No' default: '" << field << "':\t" << pt.get(field, YesNo::No, trans) << "\n";
std::cout << "Without default: '" << field << "':\t" << pt.get<YesNo>(field, trans) << "\n";
} catch(std::exception const& e) {
std::cout << "Error parsing '" << field << "':\t" << e.what() << "\n";
}
}
}
完整演示
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
#include <sstream>
#include <iostream>
using boost::property_tree::ptree;
enum class YesNo { No, Yes };
static inline std::ostream& operator<<(std::ostream& os, YesNo v) {
switch(v) {
case YesNo::Yes: return os << "Yes";
case YesNo::No: return os << "No";
}
return os << "??";
}
struct YesNoTranslator {
typedef std::string internal_type;
typedef YesNo external_type;
boost::optional<external_type> get_value(internal_type const& v) {
if (v == "Yes") return YesNo::Yes;
if (v == "No") return YesNo::No;
return boost::none;
}
boost::optional<internal_type> put_value(external_type const& v) {
switch(v) {
case YesNo::Yes: return std::string("Yes");
case YesNo::No: return std::string("No");
default: throw std::domain_error("YesNo");
}
}
};
static YesNoTranslator trans;
int main() {
std::istringstream iss(R"(
<?xml version="1.0"?>
<demo>
<positive>Yes</positive>
<negative>No</negative>
<invalid>Bogus</invalid>
</demo>
)");
ptree pt;
read_xml(iss, pt);
for (auto&& field : { "demo.positive", "demo.negative", "demo.invalid" })
{
try {
std::cout << "With 'No' default: '" << field << "':\t" << pt.get(field, YesNo::No, trans) << "\n";
std::cout << "Without default: '" << field << "':\t" << pt.get<YesNo>(field, trans) << "\n";
} catch(std::exception const& e) {
std::cout << "Error parsing '" << field << "':\t" << e.what() << "\n";
}
}
}
打印
With 'No' default: 'demo.positive': Yes
Without default: 'demo.positive': Yes
With 'No' default: 'demo.negative': No
Without default: 'demo.negative': No
With 'No' default: 'demo.invalid': No
Without default: 'demo.invalid': Error parsing 'demo.invalid': conversion of data to type "5YesNo" failed
我想使用 boosts 属性 tree 来处理我的 c++ 应用程序的设置,因为它似乎在这种情况下被广泛使用。
我的问题:在 属性 树中更改值时(通过 xml 解析或手动),有没有办法预先指定键的允许值列表? 例如。如果我想做一个简单的 "Yes/No" 设置,我是否必须使用 if - 条件检查值,或者我可以以某种方式教我的树只接受两个值 "Yes" 和 "No"提前获取特定的键,以便它在出错时抛出异常。
您可以为此使用翻译器。一个不错的博客 post 我记得这里描述了这个以在 XML 支持的 属性 树中获取自定义日期格式解析:
让我们举个例子:
enum class YesNo { No, Yes };
在这种情况下,调用代码可能如下所示:
static YesNoTranslator trans;
int main() {
std::istringstream iss(R"(
<?xml version="1.0"?>
<demo>
<positive>Yes</positive>
<negative>No</negative>
<invalid>Bogus</invalid>
</demo>
)");
ptree pt;
read_xml(iss, pt);
for (auto&& field : { "demo.positive", "demo.negative", "demo.invalid" })
{
try {
std::cout << "With 'No' default: '" << field << "':\t" << pt.get(field, YesNo::No, trans) << "\n";
std::cout << "Without default: '" << field << "':\t" << pt.get<YesNo>(field, trans) << "\n";
} catch(std::exception const& e) {
std::cout << "Error parsing '" << field << "':\t" << e.what() << "\n";
}
}
}
完整演示
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/xml_parser.hpp>
#include <sstream>
#include <iostream>
using boost::property_tree::ptree;
enum class YesNo { No, Yes };
static inline std::ostream& operator<<(std::ostream& os, YesNo v) {
switch(v) {
case YesNo::Yes: return os << "Yes";
case YesNo::No: return os << "No";
}
return os << "??";
}
struct YesNoTranslator {
typedef std::string internal_type;
typedef YesNo external_type;
boost::optional<external_type> get_value(internal_type const& v) {
if (v == "Yes") return YesNo::Yes;
if (v == "No") return YesNo::No;
return boost::none;
}
boost::optional<internal_type> put_value(external_type const& v) {
switch(v) {
case YesNo::Yes: return std::string("Yes");
case YesNo::No: return std::string("No");
default: throw std::domain_error("YesNo");
}
}
};
static YesNoTranslator trans;
int main() {
std::istringstream iss(R"(
<?xml version="1.0"?>
<demo>
<positive>Yes</positive>
<negative>No</negative>
<invalid>Bogus</invalid>
</demo>
)");
ptree pt;
read_xml(iss, pt);
for (auto&& field : { "demo.positive", "demo.negative", "demo.invalid" })
{
try {
std::cout << "With 'No' default: '" << field << "':\t" << pt.get(field, YesNo::No, trans) << "\n";
std::cout << "Without default: '" << field << "':\t" << pt.get<YesNo>(field, trans) << "\n";
} catch(std::exception const& e) {
std::cout << "Error parsing '" << field << "':\t" << e.what() << "\n";
}
}
}
打印
With 'No' default: 'demo.positive': Yes
Without default: 'demo.positive': Yes
With 'No' default: 'demo.negative': No
Without default: 'demo.negative': No
With 'No' default: 'demo.invalid': No
Without default: 'demo.invalid': Error parsing 'demo.invalid': conversion of data to type "5YesNo" failed