You can reuse (reassign) an input, output, or local variable
with different class, size, or complexity if the code generator can
unambiguously determine the properties of each occurrence of this
variable during C/C++ code generation. If so, MATLAB^{®} creates
separate uniquely named local variables in the generated code. You
can view these renamed variables in the code generation report (see MATLAB Code Variables in a Report).

A common example of variable reuse is in `if-elseif-else`

or
`switch-case`

statements. For example, the following function
`example1`

first uses the variable *t* in an
`if`

statement, where it holds a scalar double, then reuses
*t* outside the `if`

statement to hold a vector of
doubles.

function y = example1(u) %#codegen if all(all(u>0)) % First, t is used to hold a scalar double value t = mean(mean(u)) / numel(u); u = u - t; end % t is reused to hold a vector of doubles t = find(u > 0); y = sum(u(t(2:end-1)));

You cannot reuse (reassign) variables if it is not possible to determine the class, size, and complexity of an occurrence of a variable unambiguously during code generation. In this case, variables cannot be renamed and a compilation error occurs.

For example, the following `example2`

function
assigns a fixed-point value to *x* in the `if`

statement
and reuses *x* to store a matrix of doubles in the `else`

clause.
It then uses *x* after the `if-else`

statement.
This function generates a compilation error because after the `if-else`

statement,
variable *x* can have different properties depending
on which `if-else`

clause executes.

function y = example2(use_fixpoint, data) %#codegen if use_fixpoint % x is fixed-point x = fi(data, 1, 12, 3); else % x is a matrix of doubles x = data; end % When x is reused here, it is not possible to determine its % class, size, and complexity t = sum(sum(x)); y = t > 0; end

Example 3. Variable Reuse in an if Statement

To see how MATLAB renames a reused variable *t*:

Create a MATLAB file

`example1.m`

containing the following code.function y = example1(u) %#codegen if all(all(u>0)) % First, t is used to hold a scalar double value t = mean(mean(u)) / numel(u); u = u - t; end % t is reused to hold a vector of doubles t = find(u > 0); y = sum(u(t(2:end-1))); end

Compile

`example1`

.For example, to generate a MEX function, enter:

codegen -o example1x -report example1.m -args {ones(5,5)}

### Note

`codegen`

requires a MATLAB Coder™ license.When the compilation is complete,

`codegen`

generates a MEX function,`example1x`

in the current folder, and provides a link to the code generation report.Open the code generation report.

In the MATLAB code pane of the code generation report, place your pointer over the variable

*t*inside the`if`

statement.The code generation report highlights both instances of

*t*in the`if`

statement because they share the same class, size, and complexity. It displays the data type information for*t*at this point in the code. Here,*t*is a scalar double.In the MATLAB code pane of the report, place your pointer over the variable

*t*outside the for-loop.This time, the report highlights both instances of

*t*outside the`if`

statement. The report indicates that*t*might hold up to`25`

doubles. The size of*t*is`:25`

, that is, a column vector containing a maximum of`25`

doubles.Click the

**Variables**tab to view the list of variables used in`example1`

.The report displays a list of the variables in

`example1`

. There are two uniquely named local variables*t>1*and*t>2*.In the list of variables, place your pointer over

*t>1*.The code generation report highlights both instances of

*t*in the`if`

statement.In the list of variables, place your pointer over

*t>2*The code generation report highlights both instances of

*t*outside the`if`

statement.

The following variables cannot be renamed in generated code:

Persistent variables.

Global variables.

Variables passed to C code using

`coder.ref`

,`coder.rref`

,`coder.wref`

.Variables whose size is set using

`coder.varsize`

.Variables whose names are controlled using

`coder.cstructname`

.The index variable of a

`for`

-loop when it is used inside the loop body.The block outputs of a MATLAB Function block in a Simulink

^{®}model.Chart-owned variables of a MATLAB function in a Stateflow

^{®}chart.

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