throwing exception with "complex" message

[Dharmesh946]

C++Weekly

exceptions

how to do something like:

try
{
   something_that_may_throw(args…);
}
catch(const std::exception& e)
{
   throw std::runtime_error(some string built on the fly);
}

How to "build" the message (that may depend on runtime information) without having the build himself throwing?

Idea: using std::snstring but complicated with std::string_view which are not null-terminated (std::copy perhaps?).

Length

5-10 minutes

[LB--]

There is no way. The cost has to be paid for at some point, all you can do is shift it around. You could store just the format string and the arguments in the exception and have the catcher pay the cost of formatting it, for example, but exceptions inherently have this issue since allocating or copying the exception object itself can fail. You should be more worried about gracefully handling exceptions than gracefully creating exceptions. If it is critical for an error reporting mechanism to be fully accurate, don't use exceptions.