From cppreference.com
classformat_error;(since C++20)Defines the type of exception object thrown to report errors in the formatting library.
Inheritance diagram
Member functions
(constructor)
constructs a new format_error object with the given message
(public member function)operator=
replaces the format_error object
(public member function)std::format_error::format_error
format_error(conststd::string&what_arg); (1) format_error(constchar*what_arg); (2) format_error(constformat_error&other)noexcept; (3) 1) Constructs the exception object with what_arg as explanatory string. After construction, std::strcmp(what(),what_arg.c_str())==0.
2) Constructs the exception object with what_arg as explanatory string. After construction, std::strcmp(what(),what_arg)==0.
3) Copy constructor. If *this and other both have dynamic type std::format_error then std::strcmp(what(),other.what())==0. No exception can be thrown from the copy constructor.
Parameters
what_arg - explanatory string other - another exception object to copy Exceptions
Notes
Because copying std::format_error is not permitted to throw exceptions, this message is typically stored internally as a separately-allocated reference-counted string. This is also why there is no constructor taking std::string&&: it would have to copy the content anyway.
A derived standard exception class must have a publicly accessible copy constructor. It can be implicitly defined as long as the explanatory strings obtained by what() are the same for the original object and the copied object.
std::format_error::operator=
format_error&operator=(constformat_error&other)noexcept;Assigns the contents with those of other. If *this and other both have dynamic type std::format_error then std::strcmp(what(),other.what())==0 after assignment. No exception can be thrown from the copy assignment operator.
Parameters
other - another exception object to assign with Return value
*this
Notes
A derived standard exception class must have a publicly accessible copy assignment operator. It can be implicitly defined as long as the explanatory strings obtained by what() are the same for the original object and the copied object.
Inherited from
Member functions
[virtual]
destroys the exception object
(virtual public member function of std::exception)
[virtual]
returns an explanatory string
(virtual public member function of std::exception)
Example
Run this code
#include<format>#include<print>#include<string_view>#include<utility>intmain(){try{autox13{37};autoargs{std::make_format_args(x13)};std::ignore=std::vformat("{:()}",args);// throws}catch(conststd::format_error&ex){std::println("{}",ex.what());}}Possible output:
format error: failed to parse format-spec See also