I have a C function created using Compiler CDK and it's returning a large array but it's MxArray** type. How do I access all the data retunred to the calling C function?
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Here's the C calling function from main().
#include <stdio.h>
#include "libMPrime_CA_P.h"
#include "matrix.h"
int main(void)
{
libMPrime_CA_PInitialize();
mxArray *mydata;
int numargs=1;
int rtn;
rtn = mlfMPrime_CA_P(numargs,&mydata); // Function that was created using Compiler CDK returns MxArray**
printf("Function Completed rtn:%0d with numargs =%d\n",rtn,numargs);
libMPrime_CA_PTerminate();
return 0;
}
//Here's the funcrion header in the library.
extern LIB_libMPrime_CA_P_C_API bool MW_CALL_CONV mlfMPrime_CA_P(int nargout, mxArray** a);
Here's the function header written in MATLAB
function [a] = MPrime_CA_P
a is 1 x 127689 double values
....
What does nargout do and how do I access all the data in MxArray** a?
回答（1 个）
James Tursa
2020-5-22
编辑：James Tursa
2020-5-22
A function signature like that typically means that the mlfMPrime_CA_P( ) function is creating an mxArray and then returning the address of that mxArray in the variable mydata. That is, mydata is intended to be an output of the function call. So you can use mydata like an ordinary mxArray pointer and use normal API function on it in the calling function. E.g., something like:
mxArray *mydata = NULL; // You should initialize it in case the function doesn't set it
:
rtn = mlfMPrime_CA_P(numargs,&mydata);
if( mydata != NULL ) {
printf("Function returned an mxArray of class %s\n",mxGetClassName(mydata));
// Other API functions to manipulate mydata go here
mxDestroyArray(mydata);
}
17 个评论
George Nicholas
2020-5-22
James Tursa
2020-5-22
编辑：James Tursa
2020-5-22
I don't deploy code so am unfamiliar with that process. Maybe not all the API functions are supported. What if you tried something simple like mxIsDouble(mydata) instead:
printf("Function returned an mxArray, mxIsDouble = %d\n",mxIsDouble(mydata));
Do you know what type of mxArray the function is supposed to create?
George Nicholas
2020-5-22
编辑：George Nicholas
2020-5-22
James Tursa
2020-5-22
编辑：James Tursa
2020-5-22
So, you need to link with the MATLAB API object library code in order to use any of those API functions. If you can't do that, then you will be forced to hack into the mxArray in order to get at the data, but that would be a very last resort. Linking with the API library is what you should be doing, as long as the mlfMPrime_CA_P function is using the same mxArray definition.
The mex.h header is not what you need (that is used when you are going to build a mex routine with mexFunction interface).
George Nicholas
2020-5-22
James Tursa
2020-5-22
Look for a libmx library file. E.g., in the matlabroot/extern/lib/etc directories ... whatever is appropriate for your system.
George Nicholas
2020-5-22
编辑：George Nicholas
2020-5-22
James Tursa
2020-5-22
编辑：James Tursa
2020-5-22
There is no libmx file (with appropriate library extension) anywhere under matlabroot? What version of MATLAB are you running?
George Nicholas
2020-5-26
编辑：George Nicholas
2020-5-26
James Tursa
2020-5-26
编辑：James Tursa
2020-5-26
You need to change the %s format, which is for a string, to an integer format like %d.
George Nicholas
2020-5-27
James Tursa
2020-5-27
What is the definition of dataval? Why aren't you calling it as mxGetNumberOfDimensions(dataval)?
George Nicholas
2020-5-27
James Tursa
2020-5-28
That didn't answer my question. Please post the exact code that defines dataval, not a sentence with your interpretation of what it is.
George Nicholas
2020-5-28
编辑：George Nicholas
2020-5-28
James Tursa
2020-5-28
编辑：James Tursa
2020-5-28
I'm still not making myself clear. Here is what I would expect the C-code to look like:
mxArray *dataval = NULL;
:
rtn = mlfMPrime_CA_P(numargs,&dataval);
if( dataval ) {
printf("Function returned an mxArray, ndim = %d\n",mxGetNumberOfDimensions(dataval));
}
Do your data types and calling sequence look like the above?
George Nicholas
2020-5-28
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2020-5-22
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