std::format_error

Since C++20

Header: <format>

Defines the type of exception object thrown to report errors in the formatting library.

# Declarations

class format_error;

(since C++20)

# Parameters

what_arg: explanatory string
other: another exception object to copy

# Return value

*this

# 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.

# Example

#include <format>
#include <print>
#include <string_view>
#include <utility>
 
int main()
{
    try
    {
        auto x13{37};
        auto args{std::make_format_args(x13)};
        std::ignore = std::vformat("{:()}", args); // throws
    }
    catch(const std::format_error& ex)
    {
        std::println("{}", ex.what());
    }
}