I recently added some pretty printers for a type we have a lot of in our codebase (the c++ Eigen library).
Unlike the article we are using lldb rather than gdb ... and while I appreciate thats its possible _at all_ to script the debugger to do some pretty printing -- I found it quite a bit more frought to implement than initially expected ...
To take the Eigen example ... Eigen is a 'header only' library and offers Templated vector and matrix types. The types are template over (optionally), data type, number of rows, number of columns, and matrix row order (row major or column major). All that information is not actually even available at runtime -- just the type name (with the instantiated values for template arguments) ...
I ended up having to super hackily parse information out of the template type name in order to be able to pretty print the matrix appropriately in lldb ...
Problems of this nature abound when debugging c++ ... Very often with a header only library, there isn't even a symbol for methods you might want to call -- so you want to eg, call the size() method on some object within the debugger to see how big it is, you'll often be out of look due to an undefined symbol reference since the 0-overahead compilation models ensures the symbol doesn't even have to be created in the binary ...
Would be nice if there was some kind of way around that -- I guess I need to try the workaround mentioned in the article of explicitly instantiating template classes for common classes in 'debug' mode ... My fuzzy mental model derived from previous experience somehow doesn't think that will actually help the issue tho -- but I'd be happy to be wrong!
A colleague was doing this for std::map<> for libc++ in LLDB recently, and he found the same thing: he had to hackily parse the template name for the types. He told me that usually for formatters, PDB has a type ID you can use to look up the type, but templates don't.
Unlike the article we are using lldb rather than gdb ... and while I appreciate thats its possible _at all_ to script the debugger to do some pretty printing -- I found it quite a bit more frought to implement than initially expected ...
To take the Eigen example ... Eigen is a 'header only' library and offers Templated vector and matrix types. The types are template over (optionally), data type, number of rows, number of columns, and matrix row order (row major or column major). All that information is not actually even available at runtime -- just the type name (with the instantiated values for template arguments) ...
I ended up having to super hackily parse information out of the template type name in order to be able to pretty print the matrix appropriately in lldb ...
Problems of this nature abound when debugging c++ ... Very often with a header only library, there isn't even a symbol for methods you might want to call -- so you want to eg, call the size() method on some object within the debugger to see how big it is, you'll often be out of look due to an undefined symbol reference since the 0-overahead compilation models ensures the symbol doesn't even have to be created in the binary ...
Would be nice if there was some kind of way around that -- I guess I need to try the workaround mentioned in the article of explicitly instantiating template classes for common classes in 'debug' mode ... My fuzzy mental model derived from previous experience somehow doesn't think that will actually help the issue tho -- but I'd be happy to be wrong!