using #ifdef in c++ generated mexcode

Hello,

I am calling mexFunction.cpp from matlab

coder.ceval('mexMiFunction', .....);

the mex function in c++ originally looks like this,

void mexMiFunction(int nlhs, mxArray* plhs[],
    int nrhs, const mxArray* prhs[])
{
    .....
}
    

but I want to be able to run 2 different codes , depending on if we are generating code using CodeGenerator or not. It would look like this

#ifdef CODER  //takes this path if we are using code generator
int miCustomFunction(...)
    {
    .... different implementation
    }
#else
void mexMiFunction(int nlhs, mxArray* plhs[],
    int nrhs, const mxArray* prhs[])
{
    .....
}

#endif

How can I do it? thanks a lot.

Answer 1

[Varun]

Hi Ebaneo,

I understand that you want to conditionally compile different parts of your code depending on whether you are using the Code Generator or not, you can use preprocessor directives in your C++ code.

In your case, you've already provided an example with the "#ifdef" and "#else" directives. However, you need to define the "CODER" macro when generating code using the Code Generator.

In your MATLAB code, when you call the "coder.ceval" function, you need to ensure that the "CODER" macro is defined. You can do this by using

coder.updateBuildInfo('addDefines', '-CODER');

For example, in MATLAB, before calling coder.ceval, you can set the compiler options like this:

coder.updateBuildInfo('addDefines', '-CODER');
coder.ceval('mexMiFunction', ...);

This tells the compiler to define the "CODER" macro during compilation, so the code inside the "#ifdef CODER" block will be included.

Refer the following documentation to learn more about using “coder.updateBuildInfo” function:

https://www.mathworks.com/help/simulink/slref/coder.updatebuildinfo.html?s_tid=doc_ta#btx9jnw-options

Hope this helps.

[Ebaneo Enrique]

thank you very much for your help!

the only thing I would note is that

coder.updateBuildInfo('addDefines', '-CODER');

gives me an error "macro names must be identifiers"

on the oder hand, if I use

coder.updateBuildInfo('addDefines', 'CODER');

it works, thanks