Why can't I mex cpp with matlab?

I am running Matlab 2016a on Mac OS X El Capitan 10.11.6. And I have Xcode 6.4. When I input 'mex -setup' in Matlab, it goes well as followed

 >> mex -setup
MEX configured to use 'Xcode with Clang' for C language compilation.
Warning: The MATLAB C and Fortran API has changed to support MATLAB
   variables with more than 2^32-1 elements. In the near future
   you will be required to update your code to utilize the
   new API. You can find more information about this at:
   http://www.mathworks.com/help/matlab/matlab_external/upgrading-mex-files-to-use-64-bit-api.html.
To choose a different language, select one from the following:
 mex -setup C++ 
 mex -setup FORTRAN

But when I mex a cpp on my matlab， I got an error message like this:

>> GCO_UnitTest
Building with 'Xcode Clang++'.
Error using mex
In file included from /Users/Downloads/decolor/gco-v3.0/matlab/gco_matlab.cpp:5:
In file included from
/Users/Downloads/decolor/gco-v3.0/matlab/../GCoptimization.h:109:
/Users/Downloads/decolor/gco-v3.0/matlab/../energy.h:262:2: warning: 'register'
storage class specifier is deprecated [-Wdeprecated-register]
      register Value pi = (E000 + E011 + E101 + E110) - (E100 + E010 + E001 + E111);
      ^~~~~~~~~
/Users/Downloads/decolor/gco-v3.0/matlab/../energy.h:263:2: warning: 'register'
storage class specifier is deprecated [-Wdeprecated-register]
      register Value delta;
      ^~~~~~~~~
/Users/Downloads/decolor/gco-v3.0/matlab/../energy.h:264:2: warning: 'register'
storage class specifier is deprecated [-Wdeprecated-register]
      register Var u;
      ^~~~~~~~~
In file included from /Users/Downloads/decolor/gco-v3.0/matlab/gco_matlab.cpp:5:
In file included from
/Users/Downloads/decolor/gco-v3.0/matlab/../GCoptimization.h:111:
/Users/Downloads/decolor/gco-v3.0/matlab/../maxflow.cpp:366:16: warning: using the
result of an assignment as a condition without parentheses [-Wparentheses]
      if (i->parent = a0_min)
          ~~~~~~~~~~^~~~~~~~
/Users/Downloads/decolor/gco-v3.0/matlab/../maxflow.cpp:366:16: note: place
parentheses around the assignment to silence this warning
      if (i->parent = a0_min)
                    ^
          (                 )
/Users/Downloads/decolor/gco-v3.0/matlab/../maxflow.cpp:366:16: note: use '==' to
turn this assignment into an equality comparison
      if (i->parent = a0_min)
                    ^
                    ==
/Users/Downloads/decolor/gco-v3.0/matlab/../maxflow.cpp:443:16: warning: using the
result of an assignment as a condition without parentheses [-Wparentheses]
      if (i->parent = a0_min)
          ~~~~~~~~~~^~~~~~~~
/Users/Downloads/decolor/gco-v3.0/matlab/../maxflow.cpp:443:16: note: place
parentheses around the assignment to silence this warning
      if (i->parent = a0_min)
                    ^
          (                 )
/Users/Downloads/decolor/gco-v3.0/matlab/../maxflow.cpp:443:16: note: use '==' to
turn this assignment into an equality comparison
      if (i->parent = a0_min)
                    ^
                    ==
/Users/Downloads/decolor/gco-v3.0/matlab/gco_matlab.cpp:8:13: error: typedef
redefinition with different types ('int' vs 'size_t' (aka 'unsigned long'))
typedef int mwSize;
          ^
/Applications/MATLAB_R2016a.app/extern/include/tmwtypes.h:795:19: note: previous definition
is here
typedef size_t    mwSize;         /* unsigned pointer-width integer */
                ^
/Users/Downloads/decolor/gco-v3.0/matlab/gco_matlab.cpp:9:13: error: typedef
redefinition with different types ('int' vs 'size_t' (aka 'unsigned long'))
typedef int mwIndex;
          ^
/Applications/MATLAB_R2016a.app/extern/include/tmwtypes.h:796:19: note: previous definition
is here
typedef size_t    mwIndex;        /* unsigned pointer-width integer */
                ^
5 warnings and 2 errors generated.
Error in GCO_BuildLib (line 77)
eval(mexcmd);  % compile and link in one step
Error in GCO_UnitTest (line 48)
GCO_BuildLib; disp('BuildLib PASSED');

I am confused on this problem for several days and have tried some solutions but no fixed. Could someone help me with this? Thanks!

Answer 1

[Walter Roberson]

The code you are compiling is outdated.

/Users/Downloads/decolor/gco-v3.0/matlab/gco_matlab.cpp lines 8 and 9 use

typedef int mwSize;
typedef int mwIndex;

There was a time when mwSize and mwIndex were "int", but that was a number of years ago, when only 32 bit systems were supported. They were changed to size_t . You should either remove those two lines or change the int to size_t

[Adam Wei]

Thank you for your answer! I did as you told and it worked! Thanks so much!

[Quihao Zeng]

Really thanks for you answer!

Answer 2

[Ken Atwell]

MEX is working as expected.

How old is this code? Xcode's compiler is alerting you to several risky programming patterns being used. This code will need to be updated/corrected before Xcode will compile it.

[Adam Wei]

Thanks for your answer. It seems not the problem of the code, because I've tried many cpp files on my mac and showed the same error. But they could go well on other computers.

Answer 3

[Jan]

The compiler shows useful and improtant error messages. They should be considered and fixed.

1. Omit the "register" classifier, because it is deprected. If you really want to use it, disable the "-Wdeprecated-register" flag of the compiler.
2. The assignment in "if (i->parent = a0_min)" is assumed to be a typo. If you do not mean "if (i->parent == a0_min)", insert the condition in additional round parentheses, as suggested in the message. By the way: It is worth to read the messages litterally.
3. "typedef int mwSize" and "typedef size_t mwSize" is ugly, evil and confusing. Do not redefine fundamental types like "int". Do not do this. Don't.

Thank your XCode compiler for the detection of these inconsistent code and blame the other compilers, which accepted the code without warnings.

[Adam Wei]

Thank you for your detailed answer! I have fixed the problem!

Answer 4

[James Tursa]

You should not redefine mwSize and mwIndex in your code ... you should only define them if they are not already defined. One way to tell if they are defined or not is to test for the existence of the MWSIZE_MAX macro. Earlier versions of MATLAB that don't have mwSize and mwIndex defined in the mex.h stuff will not have MWSIZE_MAX defined, but later versions of MATLAB will. So wrap your definition stuff in a conditional:

#ifndef MWSIZE_MAX
    typedef int mwSize;
    typedef int mwIndex;
    typedef int mwSignedIndex;
#endif

I am using int in the above definitions instead of size_t because that is what matches the function signatures of the older versions of MATLAB for which the above is necessary.