How to get more info about 'bad_function_call' ?

[Jonathan Wakely]

On 27 January 2015 at 15:08, Linda A. Walsh wrote:
> How can I check the validity of what I am about to call and find
> out what is wrong with it before I make the call and am terminated?

By doing exactly that. Check if the std::function you're calling is
valid, e.g. if (f) or if (f == nullptr) or if (!!f) or whatever floats
your boat.

> Is there any debug information I'm missing?
> tracing in gdb at that point shows a check of some
> function against 0 (said it might be an inline function
> as I couldn't print its value), and then the call to bad function.
>
> As a library user and not a library-internals expert -- what
> steps can a user take at this point to figure out what is going on?

Look at the stack trace, find out why the std::function object you're
calling is empty at that point.

Then either fix the code so it isn't empty, or add a check so you
don't call it when it's empty.

Nothing in this question is specific to libstdc++, it's a basic "how
do I use std::function?" question and would be much more appropriate
in a general C++ forum, such as StackOverflow.