使用Boost.Spirit实现四则运算字符串的解析

#include <iostream>
#include <vector>
#include <boost/spirit.hpp>
#include <boost/spirit/phoenix.hpp>
using namespace std;
using namespace boost::spirit;
using namespace phoenix;
int main()
{
//为rule准备一个val变量，类型为double
//准确地说：是一个phoenix类(这里的member1)，它和其它phoenix类组成lambda表达式，在lambda中可以把它看成是一个double。
struct calc_closure : boost::spirit::closure<calc_closure, double>
{
member1 val;
};

//定义ContextT策略为calc_closure::context_t
rule<phrase_scanner_t, calc_closure::context_t> factor, term, exp;

//直接使用phoenix的lambda表达式作为Actor
factor = real_p[factor.val = arg1] | ('(' >> exp[factor.val = arg1] >> ')');
term   = factor[term.val = arg1] >> *(('*' >> factor[term.val *= arg1]) | ('/' >> factor[term.val /= arg1]));
exp    = term[exp.val = arg1] >> *(('+' >> term[exp.val += arg1]) | ('-' >> term[exp.val -= arg1]));

const char *szExp = "1 + (2 * (3 / (4 + 5)))";
double result;
parse_info<> r = parse( szExp , exp[assign_a(result)], space_p);

cout << szExp;
if(r.full)
{
//成功，得到结果
cout << " = " << result << endl;
}
else
{
//失败，显示错误位置
cout << endl << string(r.stop - szExp, ' ') << '^' << endl;
}
return 0;
}