What is the meaning of "-largeArrayDims"?

When I compile mex function, What is the meaning of "-largeArrayDims"? The following is other people's code. Why is "-largeArrayDims" added on 64-bit machines?

% This make.m is used under Windows

%add -largeArrayDims on 64-bit machines

mex -O -c svm.cpp -largeArrayDims mex -O -c svm_model_matlab.c -largeArrayDims mex -O svmtrain.c svm.obj svm_model_matlab.obj -largeArrayDims mex -O svmpredict.c svm.obj svm_model_matlab.obj -largeArrayDims mex -O libsvmread.c -largeArrayDims mex -O libsvmwrite.c -largeArrayDims

Answer 1

[SK]

Without -largeArrayDims, the index type (mwIndex) in files that you compile with the matlab libraries is typedefed as 'int' (in C) which is platform dependent (but often 32 bit). On the other hand if you compile with -largeArrayDims, it is typedefed as size_t which in C or C++ is guaranteed to be the largest integer type available for the platform.

On 64 bit platforms, you know for sure that 64 bit integer is available and that it will actually be useful. You can also add the switch on 32 bit platforms, but it is likely that you cant really create arrays of that size on 32 bit platforms so it may not be as useful or at worst pointless.

Answer 2

[Stalin Samuel]

http://www.mathworks.in/matlabcentral/answers/99144-how-do-i-update-mex-files-to-use-the-large-array-handling-api-largearraydims