Problem in using mxSetPr with USHORT

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Wang Yifan
Wang Yifan on 17 Feb 2022
Commented: Wang Yifan on 22 Feb 2022
I create an array in C, and the element of the array is USHORT, counting for 2 Bytes. Now, I wanna transfer this array to MATLAB workspace, using MATLAB-C API. The current method I used is to copy the value of each elements one by one in a for-loop. It is so inefficient. Therefore, I want to use pointers. However, I found the function mxSetPr demands the input type is double*. USHORT is determined by the hardware I used. Is there any similar function which can accomplish the address transformation from C to MATLAB workspace, and is valid for USHORT.

Accepted Answer

Jan on 17 Feb 2022
Either use memcpy instead of copying the data in a loop.
Or use mxSetData instead of mxSetPr, if you are really sure, that the USHORT array is not released from anywhere else. But this is fragile: if the Matlab variable is deleted later, mxFree()'ing the data pointer might cause a crash. I'd prefer memcpy.

More Answers (1)

James Tursa
James Tursa on 18 Feb 2022
To attach pointers of type other than double to an mxArray, you can use the mxSetData( ) function as Jan suggests. In your case you would create an mxArray of type mxUINT16_CLASS for this.
However, this will only work if the pointer was allocated with an official API function such as mxMalloc( ) or mxCalloc( ). If the pointer points to memory allocated by standard C/C++ routines such as malloc( ) or calloc( ), or the pointer points to local variables allocated off of the stack, then the use of mxSetData( ) with these pointers will result in an assertion fault and a MATLAB crash. In these cases, you must copy the data with a loop or memcpy( ).

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