我有一个异常类,我想在其上放置更多的信息.我可以创建Exception对象,调用其中的一些函数,然后将其抛出,而不会复制它的任何副本？
我发现唯一的方法是抛出一个指向该对象的指针：
class Exception : public std::runtime_error
{
public:
Exception(const std::string& msg) : std::runtime_error(msg) {}
void set_line(int line) {line_ = line;}
int get_line() const {return line_;}
private:
int line_ = 0;
};
std::unique_ptr<Exception> e(new Exception("message"));
e->set_line(__LINE__);
throw e;
...
catch (std::unique_ptr<Exception>& e) {...}
但是通常可以避免指针抛出异常,还有其他方法吗？
还可以通过构造函数设置所有选项,但是如果将更多的字段添加到类中,并且要对要设置的字段进行细粒度控制,则可以快速变为不可扩展：
throw Exception("message"); // or:
throw Exception("message",__LINE__); // or:
throw Exception("message",__FILE__); // or:
throw Exception("message",__LINE__,__FILE__); // etc.
解决方法
使用std :: move怎么办？
Exception e("message");
e.set_line(__LINE__);
throw std::move(e);
或者,您可以创建如下的Java-esque构建器：
class ExceptionBuilder;
class Exception : public std::runtime_error
{
public:
static ExceptionBuilder create(const std::string &msg);
int get_line() const {return line_;}
const std::string& get_file() const { return file_; }
private:
// Constructor is private so that the builder must be used.
Exception(const std::string& msg) : std::runtime_error(msg) {}
int line_ = 0;
std::string file_;
// Give builder class access to the exception internals.
friend class ExceptionBuilder;
};
// Exception builder.
class ExceptionBuilder
{
public:
ExceptionBuilder& with_line(const int line) { e_.line_ = line; return *this; }
ExceptionBuilder& with_file(const std::string &file) { e_.file_ = file; return *this; }
Exception finalize() { return std::move(e_); }
private:
// Make constructors private so that ExceptionBuilder cannot be instantiated by the user.
ExceptionBuilder(const std::string& msg) : e_(msg) { }
ExceptionBuilder(const ExceptionBuilder &) = default;
ExceptionBuilder(ExceptionBuilder &&) = default;
// Exception class can create ExceptionBuilders.
friend class Exception;
Exception e_;
};
inline ExceptionBuilder Exception::create(const std::string &msg)
{
return ExceptionBuilder(msg);
}
这样使用：
throw Exception::create("TEST")
.with_line(__LINE__)
.with_file(__FILE__)
.finalize();
