Syntax question about mexGetVariable( )
in [Matlab]
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From: Kate J. on 18 Feb 2010 13:38 I’m attempting to pass a single integer variable from a GUIDE-generated m-file to a C-MEX s-function c-file. I am using the following strategy: 1. In the gui m-file, I am assigning the variable, named Rating, with value UserRating, to the base workspace with the code: Assignin(‘base’,’Rating’,UserRating); (I have verified that this step is working fine, and have checked the value of Rating in the base workspace.) 2. Within my C-MEX s-function c-file, I use the function mexGetVariable( ) to grab the Rating value from the base workspace. It is this step (2) that is giving me problems. So far, I can successfully compile and execute the code const mxArray *Rating_ptr; Rating_ptr = mexGetVariable(“base”,”Rating”); However, when I try to view the value of Rating_ptr (by assigning it to another variable, and then viewing it in a scope within the Simulink model that calls this mex file), I am getting compiler errors when I try to include the statement outvar = Rating_ptr or *Rating_ptr I also tried declaring int *pr; and then using the statement pr = mxGetPr(Rating_ptr); While these additional statements compile fine, and I’m allowed to assign outvar = *pr with no problem, the value of *pr is always 0, whereas the Rating value that I need to access is supposed to vary with user input to the gui. I have confirmed that, even when the user is inputting values to the gui & changing the value of Rating, the value of *pr is always 0. I used the mxGetM(Rating_ptr) and mxGetN(Rating_ptr) calls to determine that the array dimensions of Rating_ptr are 1 x 1, which is consistent with the fact that I’m just passing a single variable, Rating. For your reference, I’ve been referring to the following 2 resources for syntax help: Mathworks documentation for mexGetVariable: http://www.mathworks.com/access/helpdesk/help/techdoc/apiref/mexgetvariable.html Example that uses mexGetVariable() & mxGetPr() calls: http://newsgroups.derkeiler.com/Archive/Comp/comp.soft-sys.matlab/2006-07/msg01635.html Does anyone know how my syntax is wrong, and how I can correctly access, within my C-MEX s-function c-code, the value of Rating that I’m reading in? I've tried every syntax combination I can think of. Thanks in advance for your help!
From: James Tursa on 18 Feb 2010 16:29 "Kate J." <quisquiliae3(a)hotmail.com> wrote in message <hlk1ea$hlc$1(a)fred.mathworks.com>... > I’m attempting to pass a single integer variable from a GUIDE-generated m-file to a C-MEX s-function c-file. I am using the following strategy: > > 1. In the gui m-file, I am assigning the variable, named Rating, with value UserRating, to the base workspace with the code: > Assignin(‘base’,’Rating’,UserRating); > (I have verified that this step is working fine, and have checked the value of Rating in the base workspace.) > > 2. Within my C-MEX s-function c-file, I use the function mexGetVariable( ) to grab the Rating value from the base workspace. > > It is this step (2) that is giving me problems. So far, I can successfully compile and execute the code > const mxArray *Rating_ptr; > Rating_ptr = mexGetVariable(“base”,”Rating”); > > However, when I try to view the value of Rating_ptr (by assigning it to another variable, and then viewing it in a scope within the Simulink model that calls this mex file), I am getting compiler errors when I try to include the statement > outvar = Rating_ptr or *Rating_ptr > > I also tried declaring int *pr; and then using the statement pr = mxGetPr(Rating_ptr); > > While these additional statements compile fine, and I’m allowed to assign outvar = *pr with no problem, the value of *pr is always 0, whereas the Rating value that I need to access is supposed to vary with user input to the gui. I have confirmed that, even when the user is inputting values to the gui & changing the value of Rating, the value of *pr is always 0. > > I used the mxGetM(Rating_ptr) and mxGetN(Rating_ptr) calls to determine that the array dimensions of Rating_ptr are 1 x 1, which is consistent with the fact that I’m just passing a single variable, Rating. > > For your reference, I’ve been referring to the following 2 resources for syntax help: > > Mathworks documentation for mexGetVariable: > http://www.mathworks.com/access/helpdesk/help/techdoc/apiref/mexgetvariable.html > > Example that uses mexGetVariable() & mxGetPr() calls: > http://newsgroups.derkeiler.com/Archive/Comp/comp.soft-sys.matlab/2006-07/msg01635.html > > > Does anyone know how my syntax is wrong, and how I can correctly access, within my C-MEX s-function c-code, the value of Rating that I’m reading in? I've tried every syntax combination I can think of. > Thanks in advance for your help! Need to see more of your code. What is the class of the variable Rating? Is it a double, single, char, int32, etc.? What is the type of the variable outvar? etc. etc. etc. Basically, mexGetVariable gets a copy of the workspace variable into your mex function. Using mxGetPr and then dereferencing should show the value as long as the class of the mxArray is double. James Tursa
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