cast.h

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#ifndef STDEXT_CAST_H
#define STDEXT_CAST_H
 
#include "exception.h"
#include "demangle.h"
 
#include <sstream>
#include <iostream>
#include <cstdlib>
 
namespace stdext {
 
// cast a type to another type
template<typename T, typename R>
bool cast(const T& in, R& out) {
    std::stringstream ss;
    ss << in;
    ss >> out;
    return !!ss && ss.eof();
}
 
// cast a type to string
template<typename T>
bool cast(const T& in, std::string& out) {
    std::stringstream ss;
    ss << in;
    out = ss.str();
    return true;
}
 
// cast string to string
template<>
inline bool cast(const std::string& in, std::string& out) {
    out = in;
    return true;
}
 
// special cast from string to boolean
template<>
inline bool cast(const std::string& in, bool& b) {
    if(in == "true")
        b = true;
    else if(in == "false")
        b = false;
    else
        return false;
    return true;
}
 
// special cast from string to char
template<>
inline bool cast(const std::string& in, char& c) {
    if(in.length() != 1)
        return false;
    c = in[0];
    return true;
}
 
// special cast from string to long
template<>
inline bool cast(const std::string& in, long& l) {
    if(in.find_first_not_of("-0123456789") != std::string::npos)
        return false;
    std::size_t t = in.find_last_of('-');
    if(t != std::string::npos && t != 0)
        return false;
    l = atol(in.c_str());
    return true;
}
 
// special cast from string to int
template<>
inline bool cast(const std::string& in, int& i) {
    long l;
    if(cast(in, l)) {
        i=l;
        return true;
    }
    return false;
}
 
// special cast from string to double
template<>
inline bool cast(const std::string& in, double& d) {
    if(in.find_first_not_of("-0123456789.") != std::string::npos)
        return false;
    std::size_t t = in.find_last_of('-');
    if(t != std::string::npos &&  t != 0)
        return false;
    t = in.find_first_of('.');
    if(t != std::string::npos && (t == 0 || t == in.length()-1 || in.find_first_of('.', t+1) != std::string::npos))
        return false;
    d = atof(in.c_str());
    return true;
}
 
// special cast from string to float
template<>
inline bool cast(const std::string& in, float& f) {
    double d;
    if(cast(in, d)) {
        f=(float)d;
        return true;
    }
    return false;
}
 
// special cast from boolean to string
template<>
inline bool cast(const bool& in, std::string& out) {
    out = (in ? "true" : "false");
    return true;
}
 
// used by safe_cast
class cast_exception : public exception {
public:
    virtual ~cast_exception() throw() { }
    template<class T, class R>
    void update_what() {
        std::stringstream ss;
        ss << "failed to cast value of type '" << demangle_type<T>() << "' to type '" << demangle_type<R>() << "'";
        m_what = ss.str();
    }
    virtual const char* what() const throw() { return m_what.c_str(); }
private:
    std::string m_what;
};
 
// cast a type to another type, any error throws a cast_exception
template<typename R, typename T>
R safe_cast(const T& t) {
    R r;
    if(!cast(t, r)) {
        cast_exception e;
        e.update_what<T,R>();
        throw e;
    }
    return r;
}
 
// cast a type to another type, cast errors are ignored
template<typename R, typename T>
R unsafe_cast(const T& t, R def = R()) {
    try {
        return safe_cast<R,T>(t);
    } catch(cast_exception& e) {
        std::cerr << "CAST ERROR: " << e.what() << std::endl;
        return def;
    }
}
 
}
 
#endif