How to obtain a warning message?

I would like to extract the warning message, that a function throws. For example

syms x
solve(sin(1/sqrt(x)))

generates the warning:

Warning: The solutions are parametrized by the symbols:
k = Z_

I want to put the message to a variable programmatically. How can I make this? Thanks.

P.s. I know about lastwarn but I need to handle several warnings not just the last one.

Answer 1

[Jan]

As you found out already, lastwarn contains the last message only. You could overload the function warning to create a history of messages:

function varargout = warning(varargin)
persistent MsgList
if isa(MsgList, 'double')
  MsgList = {};
end

if nargin == 2 && isempty(varargin{1}) && isa(varargin{1}, 'double')
switch varargin{2}
  case 'GetList'
    varargout{1} = MsgList;
    return;
  case 'ResetList'
    MsgList = {};
    return;
end  % No OTHERWISE!

varargout = cell(1, nargout);
[varargout{:}] = builtin('warning', varargin{:});
MsgList{length(MsgList) + 1} = lastwarn;

This adds new messages for commands like warning('off', 'backtrace') also, so much more details are required for a smart behavior. But this demonstrates the general idea.

[EDITED] I've replaced the method to obtain and clear the list of messages. Using a magic string method in the first input is not 100% clean. Now this is used for controlling:

warning([], 'GetList')
warning([], 'ClearList')

Although it is very unlikely that somebody uses the warning message '$GetList', it might be a trap

[Zoltán Csáti]

What do we indicate with $ in MATLAB? (see: case '$GetList')?

[Jan]

The leading '$' should reduce the danger for a collision with a warning message. It is more unlikely that a warning message is called '$GetList' than 'GetList'. But such "magic strings", which cause a different behavios of the function, are a bad idea. I replace this by another approach.

[Zoltán Csáti]

Thank you.