Visual C++ How to use a non void function with thread?

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Hi guys,
I want to know how can I use a non-void parameters function with a thread in Visual C++ 2010.

I think that it's best to paste directly my code, and ask you of show me how this functions goes modify for obtain same result with threads. I have problems when pass variables...please, help me.

This is the code:

XML

#include <opencv\cv.h>
#include <opencv\highgui.h>
#include <stdio.h>
#include <windows.h>
#include <process.h>

using namespace std;
using namespace cv;

//filling array
void acquisisci (Mat in[]){
in[0]=imread("C:/OPENCV/Test/imgtest/bird1.jpg",1);
in[1]=imread("C:/OPENCV/Test/imgtest/bird2.jpg",1);
in[2]=imread("C:/OPENCV/Test/imgtest/bird3.jpg",1);
in[3]=imread("C:/OPENCV/Test/imgtest/pig1.jpg",1);
in[4]=imread("C:/OPENCV/Test/imgtest/pig2.jpg",1);
in[5]=imread("C:/OPENCV/Test/imgtest/pig3.jpg",1);
   }

//grey function
void elabora (Mat& in, Mat& out){
    if (in.channels()==3){
        cvtColor(in,out,CV_BGR2GRAY); //passa al grigio
        }
  }
  //threshold function
  void sogliata(Mat& in, Mat& out){
threshold(in,out,128,255,THRESH_BINARY);//fa la soglia
 }

 //view
  void view (Mat& o){
imshow("Immagine",o);
   waitKey(600);
   }

  int main(){

Mat in[6],ou[6],out[6];

acquisisci(in);

for (int i=0;i<=5;i++){
elabora(in[i],ou[i]);
}

for (int i=0;i<=5;i++){
sogliata(ou[i],out[i]);
}

for (int i=0;i<=5;i++){
view(out[i]);
}
  return 0;

  }

How can use threads for do this works??

Posted 15-May-13 6:21am

Domus1919

Updated 20-May-13 23:51pm

v2

Add a Solution

3 solutions

Solution 1

If you do not want to use "void" you must choose another datatype to return from your method/function.

"Void" represents the datatype that is returned. If it is void, then nothing is returned. If it specifies any other datatype, it must return that.

Posted 15-May-13 6:22am

Richard C Bishop

Updated 15-May-13 6:24am

v2

Comments

Domus1919 15-May-13 12:46pm

Perhaps I was not clear: I need to launch a function that doesn't have "arguments" void, like the one I saw in the example, but "Mat" arguments (OpenCV)...

BeginThread of Visual Studio 2010 don't accept that argument functions with non-void, how can I do this?

Richard C Bishop 15-May-13 12:49pm

I am not sure what you mean. "void" and method/function arguements are not related. Do you mean "NULL" by chance?

Domus1919 15-May-13 12:52pm

I have posted example of function that I have to use.

"void example (Mat& in, Mat& out)"

When I have to start this function with beginthread, I have difficulty because when I wrote

hth1 = HANDLE_beginthreadx (NULL, 0, example, in, out,CREATE_SUSPENDED)

there is a problem because arg list it's not NULL or void.

Solution 3

Solution #1 and #2 both give you the answer but perhaps it is not clear to you. The direct answer is that you can't pass 2 parameters to a thread and can't call a function returning void. What you need to do is write a short method that returns DWORD and takes void* (aka LPVOID) as parameter. Inside that method, you unpack the data into your two values and call your method (ie. "example(x1, x2)"). See the code in Solution #2. In the my_fun() API you want to call example(in, out).

Posted 15-May-13 17:17pm

H.Brydon

Comments

Domus1919 21-May-13 5:11am

These solution for me it's clear, but don't works.

I paste here my code, and ask you your modify...

#include <opencv\cv.h>
#include <opencv\highgui.h>
#include <stdio.h>
#include <windows.h>
#include <process.h>

using namespace std;
using namespace cv;

//filling array
void acquisisci (Mat in[]){
in[0]=imread("C:/OPENCV/Test/imgtest/bird1.jpg",1);
in[1]=imread("C:/OPENCV/Test/imgtest/bird2.jpg",1);
in[2]=imread("C:/OPENCV/Test/imgtest/bird3.jpg",1);
in[3]=imread("C:/OPENCV/Test/imgtest/pig1.jpg",1);
in[4]=imread("C:/OPENCV/Test/imgtest/pig2.jpg",1);
in[5]=imread("C:/OPENCV/Test/imgtest/pig3.jpg",1);
}

//grey function
void elabora (Mat& in, Mat& out){
if (in.channels()==3){
cvtColor(in,out,CV_BGR2GRAY); //passa al grigio
}
}
//threshold function
void sogliata(Mat& in, Mat& out){
threshold(in,out,128,255,THRESH_BINARY);//fa la soglia
}

//view
void view (Mat& o){
imshow("Immagine",o);
waitKey(600);
}

int main(){

Mat in[6],ou[6],out[6];

acquisisci(in);

for (int i=0;i<=5;i++){
elabora(in[i],ou[i]);
}

for (int i=0;i<=5;i++){
sogliata(ou[i],out[i]);
}

for (int i=0;i<=5;i++){
view(out[i]);
}
return 0;

}

how can I do it with threads???

shailesh91082 23-May-13 5:49am

which part of code you want to put in thread ??

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CPallini · Accepted Answer · 2013-05-15T07:49:00

Pack your two arguments into a struct and then pass it as the void * parameter, for instance (assuming you are using the Windows API CreateThread function):

C++

// ----------- thread creation code ------------------------
DWORD WINAPI my_fun( LPVOID lpParam );
struct MyArg
{
  Mat * p_in;
  Mat * p_out;
};

//...
Mat in, out;
MyArg arg;
HANDLE thread_handle;
DWORD thread_id;

// initialize in (and out, if needed) here
arg.p_in = ∈
arg.p_out = &out;
thread_handle = CreateThread( NULL, 0, my_fun, (LPVOID) &arg, 0, &thread_id]);
// ...

C++

// ------------------- thread code ------------------------
DWORD WINAPI my_fun( LPVOID lpParam )
{
  if ( ! lpParam)
  {
   // handle error here
  }
  Mat * p_in, * p_out;
  p_in = (( MyArg *)(lpParam))->p_in;
  p_out = (( MyArg *)(lpParam))->p_out;
  // ... use p_in and p_out here
}