Chapter 4: Programming in Matlab - College of the Redwoods

400 Chapter 4 Programming in Matlab
Variable Scope in Nested Functions
So, what’s the big deal? Why should we bother to study nested functions? What
do they offer that we don’t already have with the existing functions and subfunctions
we’ve already studied?
The answer lies in variable scope. As a short example, open the editor and
enter the following lines. Save the function M-file as varScope1.m.
function varScope1
x=3;
nestfun1
function nestfun1
fprintf(’In nestfun1, x equals: %d\n’,x)
Note that we have a primary function named varScope1 which contains one
subfunction named nestfun1. The primary assigns the variable x the scalar 3,
then calls the subfunction with the command nestfun1. In turn, the subfunction
nestfun1 attempts to print the value of the variable x fprintf with a nice format
string.
Remember that the primary function varScope1 and the subfunction nestfun1
have separate workspaces. The variable x exists in the primary workspace, but
the subfunction workspace is independent of the primary workspace and thus has
no knowledge of the variable x. Thus, when we run the function, we should not
be surprised by the error message.
>> varScope1
??? Undefined function or variable ’x’.
Error in ==> varScope1>nestfun1 at 6
fprintf(’In nestfun1, x equals: %d\n’,x)
Error in ==> varScope1 at 3
nestfun1
This is precisely the error message we expected to see. The variable x exists in
the primary function workspace, but the subfunction workspace has no knowledge
of the variable x. When the subfunction attempts to print the contents of the
variable x, an error occurs.