passing unicode string from C mex function to Matlab

Hello, I need to send a unicode string from my C mex function to Matlab. At the moment, I try to use mxCreateString to create the variable to return, but unfortunately, I do not get the correct string in Matlab. The string in my C mex function is UTF8 encoded. As far as I can see, the mxCreateString takes a char* only. Does this mean, that mxCreateString can not handle unicode strings? Is there any other way to return unicode strings to Matlab?

Am I correct that Matlab itself uses UTF16 to store strings?

Thank you in advance,

Christian

Answer 1

[Friedrich]

Hi,

at least the doc states that the mxChar type is 2 byte:

http://www.mathworks.com/help/matlab/apiref/mxchar.html

What happens when you use mxCreateCharArray together with a mxGetData and a memcopy? Or you use a loop to write the data in and cast accordingly?

mxArry *tmp = mxCreateCharArray(...)
mxChar *charData = (mxChar *)mxGetData(tmp);
        for(j=0; j < nelem_tmp; j++) {
                  charData[j] = (mxChar)Your_string[j]
}

[Christian]

Friedrich, this works. I am able to pass my unicode characters to Matlab now. Thank you very much.

[Jan]

@Christian: Did you try this with non-ASCII values? The conversion from UTF-8 should actually fail tremendously with this method.

Answer 2

[Jan]

See also:

• http://www.mathworks.com/matlabcentral/answers/3198-convert-matlab-string-to-wchar-in-c-mex-under-windows-and-linux
• http://www.mathworks.com/matlabcentral/newsreader/view_thread/301249

There is the undocumented function mxArrayToString_UTF8.