Checking if 'C++ type stream' is valid when using Matlab Coder

I am using matlab coder to turn matlab code into C++. One desired function is to read a file. I can do so effectively by following the code found at:

http://www.mathworks.com/products/matlab-coder/examples.html?file=/products/demos/shipping/coder/coderdemo_readfile.html.

However, I would also like to check to make sure the stream is valid. In matlab I can simply do this by saying:

fid = coder.ceval('fopen', [FileName 0], ['a+t' 0]);

if(fid~=0)...

However, currently the compiler is telling me: "??? Expected either a logical, char, int, fi, single, or double. Found a coder.opaque."

I tried a few options:

if(fid)...

if(~fid)...

if(fid==NULL)...

But could not get it to work. Any ideas?

Answer 1

[Ryan Livingston]

Try:

 fid = coder.opaque('FILE *','NULL')
 NULL = coder.opaque('FILE *','NULL');

 fid = coder.ceval(...);

 if(fid == NULL)
   ...

after adding <stdio.h> in your project as you describe in your other post:

http://www.mathworks.com/matlabcentral/answers/64172-matlabl-coder-compilation-error-with-file

The error you are seeing is because the line:

 if(fid~=0)

is trying to compare a coder.opaque, fid, to a double, 0.