关于 exception 的一个问题 - 未名空间MITBBS历史存档

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关于 exception 的一个问题

关于 exception 的一个问题# Programming - 葵花宝典

r*r2008-02-26 08:02

1 楼

中定义了 class exception:
class exception
{
public:
exception() throw() { }
virtual ~exception() throw();
virtual const char* what() const throw();
};
问题: 为什么 what() 返回一个 const char * 类型?
为什么不返回一个 string 呢? 可以返回一个 string 吗?

t*t2008-02-26 08:02

2 楼

what if string throw another exception?

【在 r*********r 的大作中提到】

: 中定义了 class exception:
: class exception
: {
: public:
: exception() throw() { }
: virtual ~exception() throw();
: virtual const char* what() const throw();
: };
: 问题: 为什么 what() 返回一个 const char * 类型?
: 为什么不返回一个 string 呢? 可以返回一个 string 吗?

r*r2008-02-26 08:02

3 楼

但是 logic_error 和 runtime_error 都有 data member 是 string 类型.
也就是说你 throw 一个 runtime_error object 时, 要作 string 的 copy
construction,
这样也有可能 throw another exception

t*t2008-02-26 08:02

4 楼

well, the standard only says the interface (there's no obligation on data
members). implementation can do whatever they like to do...

【在 r*********r 的大作中提到】

: 但是 logic_error 和 runtime_error 都有 data member 是 string 类型.
: 也就是说你 throw 一个 runtime_error object 时, 要作 string 的 copy
: construction,
: 这样也有可能 throw another exception

r*r2008-02-26 08:02

5 楼

well, the standard says logic_error's interface is like this:
class logic_error : public exception
{
public:
explicit logic_error(const string& __arg);
}
hard to imagine an implementation that can actually avoid copying __arg.
can you?

t*t2008-02-26 08:02

6 楼

no, i can't explain now. hehe.

【在 r*********r 的大作中提到】

: well, the standard says logic_error's interface is like this:
: class logic_error : public exception
: {
: public:
: explicit logic_error(const string& __arg);
: }
: hard to imagine an implementation that can actually avoid copying __arg.
: can you?
:

r*r2008-02-26 08:02

7 楼

i came up with an idea: define a char * data member x;
and do the following in the constructor:
x = (char *)malloc(__arg.size());
strcpy(x, __arg.c_str());
and return x in what(), and call free(x) in the destructor.
maybe that works, at least it's guaranteed that no additional exception will
be thrown.