Boost库LexicalCast模块

介绍

lexical_cast库进行”字面值“之间的通用转换

头文件

#include<boost/lexical_cast.hpp>

使用

基础API

• lexical_cast

boost::lexical_cast可以在各种基本类型中转换

#include <boost/lexical_cast.hpp>
#include <iostream>
#include <string>using namespace std;int main() {string s1;string s2 = "888";int val = 123;     s1 = boost::lexical_cast<string>(1.532e5);cout << s1 << endl;s1 = boost::lexical_cast<string>(1234);cout << s1 << endl;s1 = boost::lexical_cast<string>(5.265);cout << s1 << endl;val = boost::lexical_cast<int>(s2);cout << val << endl;
}

lexcial_cast的内部使用了标准的流操作，因此它对转换对象有如下要求:

• Source是可流输出的(OutputStreamable)，即定义了一个操作符<<
• Target是可流输入的(InputStreamable)，即义了一个操作符>>
• Target是可复制的
• Target是可默认构造的，这意味着可以默认初始化该类型的对象

• bad_lexical_cast

如果转换失败，则会抛出从 std::bad_cast 派生的 boost::bad_lexical_cast 类型的异常。

    try{cout << lexical_cast<int>("0x100");cout << lexical_cast<double>("HelloWorld");cout << lexical_cast<long>("1000L");cout << lexical_cast<bool>("false") << endl;}catch (bad_lexical_cast& e){cout << "error:" << e.what() << endl;}

• try_lexical_convert

lexical_cast在名字空间boost::conversion提供try_lexical_convert()函数，可以避免抛出异常，它以bool返回值表示是否转换成功

    float f;for (auto str : {"abc", "1.2"}) {if (try_lexical_convert<float>(str, f)) {cout << "Succes"" << str << "\" to " << f << endl;} else {cout << "Fail"" << str << "\" to float" << endl;}}

自定义类型转换

如果我们想要将lexical_cast应用于自定义的类，需要实现流操作符operator

• 自定义类转字符串

#include <boost/lexical_cast.hpp>
#include <iostream>
#include <string>using namespace std;class Point {public:Point(float x, float y) : x_(x), y_(y) {}friend ostream &operator<<(ostream &output, const Point &p) {output << "(" << p.x_ << ", " << p.y_ << ")";return output;}private:const float x_;const float y_;
};int main() {using boost::bad_lexical_cast;using boost::lexical_cast;const auto s = lexical_cast<string>(Point(1.1f, 2.2f));cout << s << endl;
}

• 字符串转自定义类

class Point {public:friend istream &operator>>(istream &input, Point &p) {input >> p.x_;return input;}friend ostream &operator<<(ostream &output, const Point &p) {output << "Point(" << p.x_ << ")";return output;}Point() { x_ =0; }Point(const Point &pt) {x_ = pt.x_;}private:float x_;
};int main() {using boost::bad_lexical_cast;using boost::lexical_cast;const auto p = lexical_cast<Point>(string("3.3"));cout << p << endl;
}

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参考资料2