Difference between revisions of "cpp/error/exception/exception"
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(note about COW strings in the implementations.) |
(Added LWG issue #471 DR (part 2/3).) |
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{{cpp/error/exception/navbar}} | {{cpp/error/exception/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl | num=1 | | + | {{dcl rev multi|num=1|until1=c++11|dcl1= |
| − | exception(); | + | exception() throw(); |
| + | |dcl2= | ||
| + | exception() noexcept; | ||
}} | }} | ||
| − | {{dcl | num=2 | | + | {{dcl rev multi|num=2|until1=c++11|dcl1= |
| − | exception( const exception& other ); | + | exception( const exception& other ) throw(); |
| + | |dcl2= | ||
| + | exception( const exception& other ) noexcept; | ||
}} | }} | ||
{{dcl end}} | {{dcl end}} | ||
| Line 12: | Line 16: | ||
Constructs new exception object. | Constructs new exception object. | ||
| − | @1@ Default constructor. {{ | + | @1@ Default constructor. {{lc|what()}} returns an implementation-defined string. |
| − | @2@ Copy constructor. Initializes the contents with those of {{tt|other}} | + | @2@ Copy constructor. Initializes the contents with those of {{c|other}}. If {{c|*this}} and {{c|other}} both have dynamic type {{tt|std::exception}} then {{c|1=std::strcmp(what(), other.what()) == 0}}. |
===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | other | another exception to assign the contents of}} | + | {{par|other|another exception to assign the contents of}} |
{{par end}} | {{par end}} | ||
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===Notes=== | ===Notes=== | ||
| − | Because copying {{tt|std::exception}} is not permitted to throw exceptions, when derived classes (such as {{lc|std:runtime_error}}) have to manage a user-defined diagnostic message, it is typically implemented as a copy-on-write string. | + | Because copying {{tt|std::exception}} is not permitted to throw exceptions, when derived classes (such as {{lc|std::runtime_error}}) have to manage a user-defined diagnostic message, it is typically implemented as a copy-on-write string. |
| + | |||
| + | The Microsoft implementation includes non-standard constructors taking strings thus allowing instances to be thrown directly with a meaningful error message. The nearest standard equivalents are {{lc|std::runtime_error}} or {{lc|std::logic_error}}. | ||
| + | |||
| + | ===Defect reports=== | ||
| + | {{dr list begin}} | ||
| + | {{dr list item|wg=lwg|dr=471|std=C++98|before=there is no requirement on {{lc|what()}} of the exception copy|after=added}} | ||
| + | {{dr list end}} | ||
| − | + | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | |
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Latest revision as of 18:05, 20 February 2023
| (1) | ||
exception() throw(); |
(until C++11) | |
| exception() noexcept; |
(since C++11) | |
| (2) | ||
exception( const exception& other ) throw(); |
(until C++11) | |
| exception( const exception& other ) noexcept; |
(since C++11) | |
Constructs new exception object.
1) Default constructor. what() returns an implementation-defined string.
2) Copy constructor. Initializes the contents with those of other. If *this and other both have dynamic type
std::exception then std::strcmp(what(), other.what()) == 0.[edit] Parameters
| other | - | another exception to assign the contents of |
[edit] Notes
Because copying std::exception is not permitted to throw exceptions, when derived classes (such as std::runtime_error) have to manage a user-defined diagnostic message, it is typically implemented as a copy-on-write string.
The Microsoft implementation includes non-standard constructors taking strings thus allowing instances to be thrown directly with a meaningful error message. The nearest standard equivalents are std::runtime_error or std::logic_error.
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 471 | C++98 | there is no requirement on what() of the exception copy | added |
