How can I check if a variable exists within another variable?

I have a temp variable that changes depending on the type of data being processed. I want to check if that temp variable contains a field called sig or a field called SI. I've written the code below:

if exist('temp.sig','var') ~= 0  %checks if line or map
                N = normalize(temp.sig);
                image(app.UIAxes,N);
                handles.isLine = true;
                %display line
elseif exist('temp.SI','var') ~= 0
                N = normalize(temp.SI(1,:,:));
                image(app.UIAxes,N)
else
    
end               

The issue is that whenever I run this it immediately evaluates both statements to false, even though one or the other should be true. It seems as if the exist statement doesn't check within the temp variable for SI or sig, it just looks for the names in the workspace. I don't know what the issue is or how to fix it.

Answer 1

[Walter Roberson]

if isfield(temp, 'sig')
                N = normalize(temp.sig);
                image(app.UIAxes,N);
                handles.isLine = true;
elseif isfield(temp, 'SI')
                N = normalize(temp.SI(1,:,:));
                image(app.UIAxes,N)
end

[Raymond Mo]

Thanks for the quick answer! It works :)

Answer 2

[John D'Errico]

It fails, because exist does not apply to fields of a strcture.

help isfield
 isfield True if field is in structure array.