array pointers in matlab

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Sam Van der Jeught
Sam Van der Jeught 2011-4-19
回答： Jim Hokanson 2014-2-14
Hi all,
I'm trying to implement a dll that I have created in Labview into Matlab. When the output value is a simple integer or floating point number, this poses no problems. However, when the dll created in Labview exports an array as output, an array pointer is used:
void __stdcall Test(int16_t outputArray[], int32_t len); //Testfunction in header file
My question is how do I read out the data present at this point in memory, in Matlab? As said before, when the output is a single number, I can simply
loadlibrary SharedLib.dll SharedLib.h alias lib
output = calllib('lib', 'Test')
unloadlibrary lib
in Matlab, but this obviously doesn't work now. Any guidance towards a solution would be greatly appreciated.
Best regards,
Sam
  1 个评论
Malcolm Lidierth
Malcolm Lidierth 2011-4-19
v = zeros(10,1,'uint16');
v = calllib('lib','Test',v,int32(10));
should do the trick. MATLAB creates the libpointer automatically as I recall. On output, v is a int16 array, not a libpointer - hence no v.value property.

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回答（3 个）

Chirag Gupta
Chirag Gupta 2011-4-19
Hi Sam,
I coded up a sample library with a signature of:
void TestFunc(int outArray[],int len);
Then to use this, you need to make use of libpointers.
Sample code for using my function was:
loadlibrary('TestShared.dll','TestFile.h','alias','lib')
libfunctionsview lib
var = zeros(10,1);
% Creating a pointer from var of int32 type. In your case it would % be int16
v = libpointer('int32Ptr',var)
v.Value
v = calllib('lib','TestFunc',v,int32(10))
v.Value
unloadlibrary lib
You can find more examples with other types in the documentation
  1 个评论
Kaustubha Govind
Kaustubha Govind 2011-4-19
The documentation is here: http://www.mathworks.com/help/techdoc/matlab_external/f42650.html

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Sam Van der Jeught
Sam Van der Jeught 2011-4-19
Hi Chirag,
Thanks for the fast reply. I implemented your code and adapted it to suit my specifics:
loadlibrary('SharedLib.dll','SharedLib.h','alias','lib')
libfunctionsview lib
var = zeros(10,1);
% Creating a pointer from var of int32 type. In your case it would % be int16
1
v = libpointer('int16Ptr',var)
2
v.Value
3
v = calllib('lib','Test',v,int32(10))
4
v.Value
unloadlibrary lib
but I end up with the following error when I run the above code in Matlab:
ans =
1
v =
libpointer
ans =
2
ans =
0
0
0
0
0
0
0
0
0
0
ans =
3
v =
0
0
0
0
0
0
0
0
0
0
ans =
4
??? Attempt to reference field of non-structure array.
Error in ==> test at 12 v.Value
Maybe you have an idea of what still goes wrong.
Thanks in advance,
Sam
  1 个评论
Chirag Gupta
Chirag Gupta 2011-4-19
Can you check what exactly the function signature is returning in MATLAB.
libfunctionsview lib should show that.
Also, try whos v to check v's type after the function call.

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Jim Hokanson
Jim Hokanson 2014-2-14
Just in case anyone comes across this, I think you want the following:
For: void __stdcall Test(int16_t outputArray[], int32_t len); //Testfunction in header file
Assuming the library is referred to as 'lib'
len = 10; temp = zeros(1,len,'int16'); ptr = libpointer('int16Ptr',temp);
calllib('lib','Test',ptr,int32(len))
data = get(ptr,'Value')
The key point is that the output is void, so you don't assign an output to calllib, i.e. you don't do:
output = calllib
Since you are working with a pointer you need to go back to the pointer and extract its value.
NOTE: I wasn't sure what the value was, but if you do get(ptr) Matlab will display information about the object.

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