MEX compilation error with gcc 15.2. MATLAB version MATLAB2020b

I have updated gcc version to version 15.2 When I mex compile the code, the error related to matrix.h include files pop ups.

The error is undefined bool type.

I have added include of stdbool.h to the source as well and still the same error persist.

I have some other c files which are still passing on the same machine.

Answer 1

[Aditya]

Hi Divya,

This is a common issue when compiling MEX files for MATLAB or Octave with newer versions of GCC (like GCC 15.x). The error about bool being undefined, even after including <stdbool.h>, is usually caused by a conflict between MATLAB's (or Octave's) own type definitions and those in the system headers.Root Cause

• matrix.h (provided by MATLAB/Octave) sometimes defines its own bool type or expects an older C standard.
• GCC 15.x is stricter and may expose conflicts between the C99 bool (from <stdbool.h>) and any custom bool definitions.
• If you have #define bool or similar in your code or in matrix.h, it can cause this error.

1. Include Order Matters

Always include matrix.h before including <stdbool.h> or any other system headers

#include "matrix.h"
#include <stdbool.h>

2.Check for Redefinition

Make sure neither your code nor matrix.h is redefining bool.

If you see something like:

typedef int bool;
#define true 1
#define false 0

remove or guard it with:

#ifndef __cplusplus
#include <stdbool.h>
#endif

3.Check MATLAB/Octave Version Compatibility

Older versions of MATLAB/Octave may not be compatible with newer GCC.

• Check if there's an update or patch for MATLAB/Octave for GCC 15.x support.
• If not, consider downgrading GCC (e.g., to GCC 11 or 12) for MEX compilation.