C Math Library Reference

Constructing a C Prototype

One C prototype supports all the possible ways to call a particular MATLAB C Math Library function. You can reconstruct the C prototype by examining the MATLAB syntax for a function.

For example, the MATLAB function svd() has the following syntax:

s = svd(X)
[U,S,V] = svd(X)
[U,S,V] = svd(X,0)

To construct the C prototype for mlfSvd(), follow this procedure.

1. Find the MATLAB syntax that includes the largest number of return values and input arguments.

   [U,S,V] = svd(X,0)
   

2. Use the first return value, U, as the return value from the C version of the function. (C routines can only have one return value.) The data type for the return value is mxArray *.
3. Add the remaining return values, S and V, as output arguments to the C function. Output arguments appear before any input arguments in the argument list. The second return value becomes the first output argument, as so on. The data type for the C output arguments is mxArray **.
4. Specify the maximum number of input arguments in the C routine prototype. The data type for input arguments is mxArray *.

Here is the complete C prototype for the svd function. Compare it to the original MATLAB syntax.

mxArray *mlfSvd(mxArray **S, mxArray **V, mxArray *X,
                mxArray *Zero);

Note    Contrast the data type for an output argument with the data type for an input argument. The type for an output argument is the address of a pointer to an mxArray. The type for an input argument is a pointer to an mxArray.

C Math Library Calling Conventions

Translating MATLAB Syntax into C Syntax