env.hpp

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#ifndef _POWERDXX_SYS_ENV_HPP_
#define _POWERDXX_SYS_ENV_HPP_
 
#include "error.hpp"    /* sys::sc_error */
 
#include <cstdlib>      /* getenv(), setenv() etc. */
 
namespace sys {
 
namespace env {
 
struct error {};
 
class Var {
    private:
    char const * const name;
 
    public:
    template <size_t Size>
    Var(char const (& name)[Size]) : name{name} {}
 
    Var(Var const &) = delete;
 
    Var & operator =(Var const &) = delete;
 
    operator char const *() const {
        return getenv(this->name);
    }
 
    Var & operator =(char const * const assign) {
        auto const result =
            assign
            ? setenv(this->name, assign, 1)
            : unsetenv(this->name);
        if (0 != result) {
            throw sc_error<error>{errno};
        }
        return *this;
    }
 
    Var & erase() {
        return *this = nullptr;
    }
 
    char const * c_str() const {
        return *this;
    }
};
 
struct Vars {
    template <typename T>
    Var const operator [](T const & name) const {
        return {name};
    }
 
    template <typename T>
    Var operator [](T const & name) {
        return {name};
    }
} vars; 
} /* namespace env */
 
} /* namespace sys */
 
#endif /* _POWERDXX_SYS_ENV_HPP_ */