Alter values of variables in mexFunction from within a subfunction
显示 更早的评论
Hello everyone,
I'm afraid this is a very basic question, but I couldn't find an answer to this, and I just don't get it working on my own:
I want to call a function minf.m via mexCallMATLAB within a subfunction minfcall, which is called from within a mexFunction. What I want to achieve is to alter the values of a and b by calling minfcall. When I run the code given below, the values of a and b displayed by mexPrintf from within minfcall are correct, but after exiting the function, the displayed values in mexFunction are the same as they were before calling minfcall.
Here's the code of the mexFunction:
#include "mex.h"
#include <string.h>
void minfcall(double *a, double *b){
mxArray *inp[1], *outp[2];
inp[0] = mxCreateDoubleMatrix(1, 1, mxREAL);
memcpy(mxGetPr(inp[0]), a, sizeof(double));
mexPrintf("Before mexCallMATLAB:\n");
mexPrintf("a: %f\nb: %f\n", *a, *b);
mexCallMATLAB(2,outp,1,inp,"minf");
a = mxGetPr(outp[0]);
b = mxGetPr(outp[1]);
mexPrintf("After mexCallMATLAB:\n");
mexPrintf("a: %f\nb: %f\n", *a, *b);
}
void mexFunction(int nlhs,mxArray *plhs[],int nrhs,const mxArray *prhs[]){
double *a, *b;
a = mxGetPr(prhs[0]);
b = mxCalloc(1, sizeof(double));
minfcall(a, b);
mexPrintf("After exiting minfcall:\n");
mexPrintf("a: %f\nb: %f\n", *a, *b);
plhs[0] = mxCreateDoubleMatrix(1, 1, mxREAL);
memcpy(mxGetPr(plhs[0]), a, sizeof(double));
plhs[1] = mxCreateDoubleMatrix(1, 1, mxREAL);
memcpy(mxGetPr(plhs[1]), b, sizeof(double));
}
The m-File does the following:
function [a, b] = minf(a)
a = 2 * a;
b = 2 * a;
end
Can you tell me what I am doing wrong here?
Thank you very much for your support!
采纳的回答
Kaustubha Govind
2013-8-16
You probably need to do this:
/* Copy the outputs of minf into a and b */
*a = *(mxGetPr(outp[0]));
*b = *(mxGetPr(outp[1]));
Instead of this:
/* Replace the pointer addresses of a and b with those of the output mxArrays */
a = mxGetPr(outp[0]);
b = mxGetPr(outp[1]);
Also, remember to destroy the output mxArrays at the end of minfcall so you're not leaking memory:
mxDestroyArray(outp[0]);
mxDestroyArray(outp[1]);
2 个评论
James Tursa
2013-8-18
And also the input mxArray:
mxDestroyArray(inp[0]);
Adrian Buerger
2013-8-19
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Matrix Indexing 的更多信息
产品
2013-8-12
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
