Why do I get a compilation error when I compile my Real-Time Workshop 6.6 (R2007a) generated code containing '_isnan' with my hand-written code?

When I then try to link my hand-written code with Real-Time Workshop generated code that contains 'rt_nonfinite.c' , I get the following error at compile time:

 ./fadec_autocode/fadec_src/lib/libfadec.a(rt_nonfinite.o): In function

 `rtIsNaN':

 /sim/sandbox/AE1107/C/src/fadec_autocode/fadec_src/rt_nonfinite.c:170:

 undefined reference to `_isnan'

 ./fadec_autocode/fadec_src/lib/libfadec.a(rt_nonfinite.o): In function

 `rtIsNaNF':

 /sim/sandbox/AE1107/C/src/fadec_autocode/fadec_src/rt_nonfinite.c:180:

 undefined reference to `_isnan'

Previous uses of real-time workshop on a different version of the same simulink model

yielded different results for the rtIsNaN and rtIsNaNF functions.

Previously, the real-time workshop output rtIsNan and rtIsNaNF as shown

below and did not actually use _isnan:

/* Function: rtIsNaN ==================================================

   * Abstract:

   *Test if value is not a number

   */

boolean_T rtIsNaN(real_T value)

{

    return((value!=value) ? 1U : 0U);

}

As opposed to what I'm getting now that is causing the issue:

/* Function: rtIsNaN ==================================================

   * Abstract:

   *Test if value is not a number

   */

boolean_T rtIsNaN(real_T value)

{

    return _isnan(value)? TRUE:FALSE;

}

Why is the implementation different now? What do I do to resolve this situation?

Answer 1

[MathWorks Support Team]

The different implementation of 'rtIsNan' function is due to using Microsoft Visual C++ compiler during code generation. If Microsoft Visual Compiler is used for code generation, then RTW generated code contains reference to _isnan() function which is shipped with the compiler.

This can be verified in the MSDN documentation page below:

 <http://msdn.microsoft.com/en-us/library/aa298428%28VS.60%29.aspx>

For example, following is the generated code with Real-Time Workshop R2007a, R2007b, R2008a and R2008b, when Microsoft Visual C++ 2005 was NOT selected as the compiler:

boolean_T rtIsNaN(real_T value)

{

     return((value!=value) ? 1U : 0U);

}

Following is the generated code in R2007a,R2007b and R2008a, when Microsoft Visual C++ 2005 was the selected compiler:

boolean_T rtIsNaN(real_T value)

{

      /* For MSVC 6.0, must use the compiler specific comparison function */

      return _isnan(value)? 1U:0U;

}

As you can observe above, when MS Visual Compiler is used, there is a reference to _isnan. Therefore when you package this into an archive for compilation using a different compiler, this would result in an error.

However in R2008b, even with MS VC as the selected compiler, the code generated contains appropriate pre-processor directives to handle this situation. Following is the code generated in R2008b when MS VC is selected as compiler::

boolean_T rtIsNaN(real_T value)

{

#if defined(_MSC_VER) && (_MSC_VER <= 1200)

      /* For MSVC 6.0, use a compiler specific comparison function */

      return _isnan(value)? 1U:0U;

    #else

      return((value!=value) ? 1U : 0U);

    #endif

}

_MSC_VER is MS VC specific directive explained in the link below:

 <http://msdn.microsoft.com/en-us/library/b0084kay.aspx>

To summarize, there are two workarounds to this issue:

1. Execute "mex -setup" in your MATLAB and change the current compiler to a non-Microsoft compiler.

2. Please generate code using R2008b or later versions.