xcode - MEX compile error: unknown type name 'char16_t'

Question

I cannot compile any MATLAB MEX code due to the following error:

In file included from /Applications/MATLAB_R2013a.app/extern/include/mex.h:58:
In file included from /Applications/MATLAB_R2013a.app/extern/include/matrix.h:294:
/Applications/MATLAB_R2013a.app/extern/include/tmwtypes.h:819:9: error: unknown type name 'char16_t'
typedef char16_t CHAR16_T;

The only thing that has changed on my machine as far as I can remember is that Xcode was updated to version 5.1 (5B130a).

Any fix for the time being to compile MEX code in MATLAB?

[Running on OS 10.9.2 with Apple LLVM version 5.1 (clang-503.0.38) (based on LLVM 3.4svn)]

Answer 1

By default, the upgraded Clang doesn't set char16_t, which is required by MATLAB.

Quick fix

This works for C or C++ code but needs to be done on each mex command line.

>> mex -Dchar16_t=uint16_t ...

Other solutions below put this definition into the mex configuration or enable C++11.

Permanent solution

Options:

• Add -std=c++11 to CXXFLAGS in your mex configuration file AND compile .cpp files instead of .c. The mex config file is mexopts.sh (pre-R2014a) or the .xml file indicated by mex -setup (R2014a+). This is what worked for OP, but the next option works too. Be sure to edit the active/installed config, not the system-wide reference. Try the next solution if you can't tell.
• Use a #define or typedef to create char16_t before including mex.h (see "other workaround" below).
• In some future version of MATLAB, this will have been fixed. Re-run mex -setup to have MATLAB reconfigure it for you and it works. As of R2014a, this doesn't do the trick.
• As a last resort, you can always modify the MATLAB installation, hacking MATLAB's tmwtypes.h as Dennis suggests, but I strongly suggest NOT modifying the MATLAB installation.

Note: If you are using C and cannot or don't want to change to C++, follow the solution in this other answer, OR see the alternative workaround below.

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The other workaround

If for some reason you are not able to enable the C++11 standard, you can use the preprocessor to define char16_t. Either put #define char16_t uint16_t before #include "mex.h", or set it with the compiler command line:

-Dchar16_t=uint16_t

Alternatively, use a typedef, again before including mex.h:

typedef uint16_t char16_t;

If these solutions don't work, try changing uint16_t to UINT16_T. Further yet, others have reported that simply including uchar.h brings in the type, but others don't have that header.