C++ struct function with return struct ...

mrjj · 27 Sept 2016, 10:06

Hi
A struct is a type
and it will not just convert between them.

Your naming of the structs is very verbose and hard to read & understand as you make
the type look like function name.

it seems you define
Find_Angle_Central_Point_Targhet Find_A_Cent_P(xx)

so return type is Find_Angle_Central_Point_Targhet
and in the function you define
Get_Angle_Central_Point_Targhet Get_A_Cent_P;
return Get_A_Cent_P; << this is not correct type to return.

gfxx · 27 Sept 2016, 10:41

@mrjj ok I suspect these ... I understand not possible return other struct type .... but I can define these struct and use these struct func?:

struct a{
int x;
double y;
cv::Point cerr0;
cv::Point cerr1;
cv::Point cerr2;
cv::Point cerr3;
}

........

a afunc (cv::Point cerr0){  /* <---------- no pass all value of a struct only one .... but return all*/
/*my operation .....*/
afunc.x = some_value0;
afunc.y = some_value1;
afunc.cerr0 = some_value0;
afunc.cerr1 = some_value1;
afunc.cerr2 = some_value2;
afunc.cerr3 = some_value3;

return afunc;
}

These is valid use of struct func??

regards
Giorgio

mrjj · wrote on 27 Sept 2016, 10:11

Yes, thats correct but its a type so it wont convert.

so if you say

struct A;
struct B;

A myfunc() {
A mine;
return mine; // ok correct type
}

A myfunc() {
B mine;
return mine; // error B is not A type
}

jsulm · 27 Sept 2016, 12:26

@gfxx said in C++ struct function with return struct ...:

a afunc (cv::Point cerr0){ /* <---------- no pass all value of a struct only one .... but return all*/
/my operation ...../
afunc.x = some_value0;
afunc.y = some_value1;
afunc.cerr0 = some_value0;
afunc.cerr1 = some_value1;
afunc.cerr2 = some_value2;
afunc.cerr3 = some_value3;

return afunc;
}

This does not make any sense. You probably mean:

a afunc (cv::Point cerr0){
    /*my operation .....*/
    a result;
    result.x = some_value0;
    result.y = some_value1;
    result.cerr0 = some_value0;
    result.cerr1 = some_value1;
    result.cerr2 = some_value2;
    result.cerr3 = some_value3;

    return result;
}

gfxx · J jsulm 27 Sept 2016, 10:41

@jsulm said in C++ struct function with return struct ...:

@gfxx said in C++ struct function with return struct ...:

a afunc (cv::Point cerr0){ /* <---------- no pass all value of a struct only one .... but return all*/
/my operation ...../
afunc.x = some_value0;
afunc.y = some_value1;
afunc.cerr0 = some_value0;
afunc.cerr1 = some_value1;
afunc.cerr2 = some_value2;
afunc.cerr3 = some_value3;

return afunc;
}

This does not make any sense. You probably mean:
a afunc (cv::Point cerr0){
    /*my operation .....*/
    a result;
    result.x = some_value0;
    result.y = some_value1;
    result.cerr0 = some_value0;
    result.cerr1 = some_value1;
    result.cerr2 = some_value2;
    result.cerr3 = some_value3;

    return result;
}

You are perfectly in right .... but anyhow the function is write in my file.h and I would reuse it in file.ccp ... but if in file.cpp i write:

 afunc (cv::Point myvalue);

/* I expect to be able to write these:*/

myvar1 = result.x;
myvar2 = result.y;
etc. etc....

/*but these is not possible .... or qt not permit it*/

Regards
Giorgio

m.sue · 27 Sept 2016, 12:52

Hi,
"result" is a local variable in "afunc". You cannot expect it to be known outside of "afunc". This is no restriction of Qt but a feature of the C++ language. But you can write something like this:

a result=afunc(myvalue);
myvar1 = result.x;
myvar2 = result.y;

-Michael.

gfxx · 27 Sept 2016, 13:31

@m.sue Tanks A lot I have just read in an ebook this peculiarity of the struct .... I have many elements struct each one with a calculation and a return .... something like these:

struct a{
int x;
double y;
cv::Point cerr0;
cv::Point cerr1;
cv::Point cerr2;
cv::Point cerr3;
cv::Point result1() { return /* some long calculation*/};
cv::Point result2() {return  /* some long calculation*/};
cv::Point result3() {return  /* some long calculation*/};

}

........

afunc (cv::Point cerr0){  /* so in my file.cpp i can write these*/
some_value0 = afunc.result1;
some_value1 = afunc.result2;
some_value2 = afunc.result3;

In my case I think is a little bit more long as I expect .... :( ..so I try your suggest to try to simplify my function ...

Regards
Giorgio

gfxx · G gfxx 27 Sept 2016, 12:52

@gfxx ...NOT WORK ...

my real code:

/******************in my file.h*-***********************/

 FindAngleCPointTarghet FindCentPoint( cv::Point2f Square_Points[4], bool a, bool b, bool c, bool d)
    {

        FindAngleCPointTarghet FindTarghet;

        F_lung1 = 0;
        F_lung2 = 0;
        F_lung3 = 0;
        F_lung4 = 0;
        F_lung5 = 0;
        F_barix = 0;
        F_bariy = 0;
        F_intbarix = 0;
        F_intbariy = 0;
        F_bariangle = 0;
        bool choose0 = false, choose1 = false, choose2 = false, choose3 = false;

        F_lung1 = std::pow((std::pow((Square_Points[0].x - Square_Points[1].x),2) + std::pow((Square_Points[0].y - Square_Points[1].y),2)), 0.5);
        F_lung2 = std::pow((std::pow((Square_Points[1].x - Square_Points[2].x),2) + std::pow((Square_Points[1].y - Square_Points[2].y),2)), 0.5);

        if (F_lung2 > F_lung1)
        {
            F_lung3 = F_lung2;
            F_lung4 = std::pow((std::pow((-Square_Points[1].x + Square_Points[2].x),2) + std::pow((0),2)), 0.5);
            F_lung5 = std::pow((std::pow((-Square_Points[1].y + Square_Points[2].y),2) + std::pow((0),2)), 0.5);
            F_barix = ((Square_Points[0].x + Square_Points[1].x + Square_Points[2].x + Square_Points[3].x)/4);
            F_bariy = ((Square_Points[0].y + Square_Points[1].y + Square_Points[2].y + Square_Points[3].y)/4);
            F_intbarix = round(F_barix);
            F_intbariy = round(F_bariy);
            F_bariangle = (std::atan2((Square_Points[2].y - Square_Points[1].y),(Square_Points[2].x - Square_Points[1].x))*180.00/3.1415926535);
            F_centrale = cv::Point(F_intbarix, F_intbariy);
            F_bariangle_template = F_bariangle;
            if(a)
            {

..................
/*the calculation proceed for 180 row with the same variable declared here ... the result ( FindTarghet.Get_centrale etc)  value change if a-b or a-d or etc etc bool value is true or false ....*/
..................

        FindTarghet.Get_centrale = F_centrale;
        FindTarghet.Get_mezzo_rect_risc = F_mezzo_rect_risc;
        FindTarghet.Get_mezzo_rect_risc1 = F_mezzo_rect_risc1;
        FindTarghet.Get_mezzo_rect_risc_pt2 = F_mezzo_rect_risc_pt2;
        FindTarghet.Get_mezzo_rect_risc_pt3 = F_mezzo_rect_risc_pt3;
        FindTarghet.X_Point = F_intbarix;
        FindTarghet.Y_point = F_intbariy;
        FindTarghet.Angle = F_bariangle_template;
        FindTarghet.Major_Side1 = false;
        FindTarghet.Major_Side2 = false;
        FindTarghet.Get_Upper_Half_Square  = false;
        FindTarghet.Get_Lower_Half_Square = false;

        return FindTarghet;


/* than in my file.ccp*******************/

FindAngleCPointTarghet TarghetResutl = FindCentPoint(rect_points, targhet_verticale, targhet_orizzontale);
centrale =  TarghetResutl.Get_centrale;
mezzo_rect_risc = TarghetResutl.Get_mezzo_rect_risc;
mezzo_rect_risc1 = TarghetResutl.Get_mezzo_rect_risc1;
mezzo_rect_risc_pt2 = TarghetResutl.Get_mezzo_rect_risc_pt2;
mezzo_rect_risc_pt3 = TarghetResutl.Get_mezzo_rect_risc_pt3;
intbarix = TarghetResutl.X_Point;
intbariy = TarghetResutl.Y_point;
bariangle = TarghetResutl.Angle;

/***********the error .... 380 error signed .... a memeory allocation id/name problem I think****************/
(.bss+0x120):-1: error: multiple definition of `F_lung4'
(.bss+0x128):-1: error: multiple definition of `F_lung3' .... etc etc.... all identical error but for all variable used during calculation ....

    }

I'm explain my better ... I try to make in file.h a struct function with struct return value .... As you see

mrjj · wrote on 27 Sept 2016, 13:57

If you include data in .h file, you can get this error
multiple definition of XXX

Im not sure why this is so complex.

--
MYS.h

struct MyStruct { // DEFINE
int Value;
};

MyStruct MyFunc(); // DEFINE

--
MYS.cpp

MyStruct MyFunc() { // IMPLEMENT
MyStruct localcopy;
localcopy.Value=100;
return localcopy;
}

-- in some file--
#include "MYS.h"

void buttonClick() {
MyStruct usedhere = MyFunc(); // USING

}

gfxx · wrote on 27 Sept 2016, 14:29

MYS = MYQThread so....

--
 MYQThread .h

struct MyStruct { // DEFINE
int Value;
};
/* now I try to do these*/
MyStruct MyFunc(with  parameter){some calculation with pnota bene arameter and some other local variable}; // DEFINE
--
 MYQThread .cpp

MyStruct MyFunc() { // IMPLEMENT /* so your answer is : " in these local copy make your calculation" ... is right?*/
MyStruct localcopy;
localcopy.Value=100;
return localcopy;
}

-- in these  MYQThread.cpp-- /* but my file.h and file.cpp is the same so is not possible do these ....*/
#include " MYQThread .h"

void buttonClick() {
MyStruct usedhere = MyFunc(); // USING

}

If I understand well your reply you think mi struct function is utilize in other part of my app ... but is define in QThread.h and implement + utilized in QThread.cpp

Regards
Giorgio

Note:
@mrjj perhaps your answer sounds like you'd better build a class that a struct func ....

mrjj · wrote on 27 Sept 2016, 14:57

make sure that
MYQThread .cpp

MyStruct MyFunc(same params as in .h) {...}

No sure i understand
/* but my file.h and file.cpp is the same so is not possible do these*/

why is file.cpp and file.h the same?

Also for the use

void buttonClick() {
MyStruct usedhere = MyFunc( ACTUAL PARAMETERS); // USING

}

gfxx · wrote on 27 Sept 2016, 16:14

/***********MYQThread .h*****************/

struct FindACPTarghet{
    cv::Point2f Square_Points[4];
    bool Find_Upper_Half_Square;
    bool Find_Lower_Half_Square;
    cv::Point Get_centrale;
    cv::Point Get_mezzo_rect_risc;
    cv::Point Get_mezzo_rect_risc1;
    cv::Point Get_mezzo_rect_risc_pt2;
    cv::Point Get_mezzo_rect_risc_pt3;
    double X_Point;
    double Y_point;
    double Angle;
    bool Major_Side1;
    bool Major_Side2;
    bool Get_Upper_Half_Square;
    bool Get_Lower_Half_Square;
    //Get_Angle_Central_Point_Targhet GetDataTarghet;
}/*FindCentPoint*/;

class datathread : public QThread
{
        Q_OBJECT
public:
    explicit datathread(QObject *parent = 0, bool bthw = false);
    void run();
    bool Stop;

    FindACPTarghet FindCentPoint( cv::Point2f Square_Points[4], bool Find_Upper_Half_Square, bool Find_Lower_Half_Square);

/***********MYQThread .cpp*****************/

FindACPTarghet FindCentPoint( cv::Point2f Square_Points[4], bool Find_Upper_Half_Square, bool Find_Lower_Half_Square)
{

    FindACPTarghet FindTarghet;  <----------------------------------------

    F_lung1 = 0;
    F_lung2 = 0;
    F_lung3 = 0;
    F_lung4 = 0;
    F_lung5 = 0;
    F_barix = 0;
    F_bariy = 0;
    F_intbarix = 0;
    F_intbariy = 0;
    F_bariangle = 0;
    bool choose0 = false, choose1 = false, choose2 = false, choose3 = false;

    F_lung1 = std::pow((std::pow((Square_Points[0].x - Square_Points[1].x),2) + std::pow((Square_Points[0].y - Square_Points[1].y),2)), 0.5);
    F_lung2 = std::pow((std::pow((Square_Points[1].x - Square_Points[2].x),2) + std::pow((Square_Points[1].y - Square_Points[2].y),2)), 0.5);

    if (F_lung2 > F_lung1)
    {..................
........................

    FindTarghet.Get_centrale = F_centrale;  <--------------------------------- /*******************************undefined error reference**********************/
    FindTarghet.Get_mezzo_rect_risc = F_mezzo_rect_risc;
    FindTarghet.Get_mezzo_rect_risc1 = F_mezzo_rect_risc1;
    FindTarghet.Get_mezzo_rect_risc_pt2 = F_mezzo_rect_risc_pt2;
    FindTarghet.Get_mezzo_rect_risc_pt3 = F_mezzo_rect_risc_pt3;
    FindTarghet.X_Point = F_intbarix;
    FindTarghet.Y_point = F_intbariy;
    FindTarghet.Angle = F_bariangle_template;
    FindTarghet.Major_Side1 = false;
    FindTarghet.Major_Side2 = false;
    FindTarghet.Get_Upper_Half_Square  = false;
    FindTarghet.Get_Lower_Half_Square = false;

    return FindTarghet;

}

/***********MYQThread .cpp    qthread::run*****************/
void datathread::run()   
{
...
...
...

FindACPTarghet OneTarghet = FindCentPoint(rect_points, true, false);
                                  centrale =  OneTarghet.Get_centrale;
                                  mezzo_rect_risc = OneTarghet.Get_mezzo_rect_risc;
                                  mezzo_rect_risc1 = OneTarghet.Get_mezzo_rect_risc1;
                                  mezzo_rect_risc_pt2 = OneTarghet.Get_mezzo_rect_risc_pt2;
                                  mezzo_rect_risc_pt3 = OneTarghet.Get_mezzo_rect_risc_pt3;
                                  intbarix = OneTarghet.X_Point;
                                  intbariy = OneTarghet.Y_point;
                                  bariangle = OneTarghet.Angle;

Not understand very well why I can't use return with struct ....

Regards
Giorgio

mrjj · 27 Sept 2016, 16:38

But you can use struct as return. :)

FindTarghet.Get_centrale = F_centrale;

what is F_central?
I dont see you define it ?
so that would explain "undefined"

gfxx · 27 Sept 2016, 16:44

@mrjj mmm....


/********* as global var in MYQThread .cpp*****************/
int F_intbarix = 0, F_intbariy = 0;
double F_lung1 = 0, F_lung11 = 0, F_lung2 = 0, F_lung3 = 0, F_lung4 = 0, F_lung5 = 0, F_barix = 0, F_bariy = 0, F_bariangle = 0, F_bariangle_template = 0;
int DeF_barix = 0, DeF_bariy = 0, DeF_bariangle = 0, DeF_bariangle_template = 0;
int X_mezzo_rect_risc = 0, Y_mezzo_rect_risc = 0, X_mezzo_rect_risc1 = 0, Y_mezzo_rect_risc1 = 0;
int X_mezzo_rect_risc_pt2 = 0, Y_mezzo_rect_risc_pt2 = 0, X_mezzo_rect_risc_pt3 = 0, Y_mezzo_rect_risc_pt3 = 0;
int DeF_Major_Side1 = 0, DeF_Major_Side2 = 0, DeF_Get_Upper_Half_Square = 0, DeF_Get_Lower_Half_Square = 0;

cv::Point F_centrale = cv::Point(0 ,0); <------------------------------------------------------- /****** and use these variable into calculation and as result too... so i put it into return struc as you see****/

cv::Point F_mezzo_rect_risc = cv::Point(0 ,0);
cv::Point F_mezzo_rect_risc1 = cv::Point(0 ,0);
cv::Point F_mezzo_rect_risc_pt2 = cv::Point(0 ,0);

Regards
giorgio

gfxx · 27 Sept 2016, 17:34

@gfxx so I try to define F_centrale into struc func..

FindACPTarghet FindCentPoint( cv::Point2f Square_Points[4], bool Find_Upper_Half_Square, bool Find_Lower_Half_Square)
{

    FindACPTarghet FindTarghet;  <----------------------------------------

   int F_intbarix = 0, F_intbariy = 0;
    double F_lung1 = 0, F_lung11 = 0, F_lung2 = 0, F_lung3 = 0, F_lung4 = 0, F_lung5 = 0, F_barix = 0, F_bariy = 0, F_bariangle = 0, F_bariangle_template = 0;
    int DeF_barix = 0, DeF_bariy = 0, DeF_bariangle = 0, DeF_bariangle_template = 0;
    int X_mezzo_rect_risc = 0, Y_mezzo_rect_risc = 0, X_mezzo_rect_risc1 = 0, Y_mezzo_rect_risc1 = 0;
    int X_mezzo_rect_risc_pt2 = 0, Y_mezzo_rect_risc_pt2 = 0, X_mezzo_rect_risc_pt3 = 0, Y_mezzo_rect_risc_pt3 = 0;
    int DeF_Major_Side1 = 0, DeF_Major_Side2 = 0, DeF_Get_Upper_Half_Square = 0, DeF_Get_Lower_Half_Square = 0;

    cv::Point F_centrale = cv::Point(0 ,0);

    cv::Point F_mezzo_rect_risc = cv::Point(0 ,0);
    cv::Point F_mezzo_rect_risc1 = cv::Point(0 ,0);
    cv::Point F_mezzo_rect_risc_pt2 = cv::Point(0 ,0);
    cv::Point F_mezzo_rect_risc_pt3 = cv::Point(0 ,0);
    cv::Point F_un_quarto_rect_risc = cv::Point(0 ,0);
    cv::Point F_un_quarto_rect_risc1 = cv::Point(0 ,0);
    cv::Point F_un_quarto_rect_risc_pt2 = cv::Point(0 ,0);
    cv::Point F_un_quarto_rect_risc_pt3 = cv::Point(0 ,0);
    bool choose0 = false, choose1 = false, choose2 = false, choose3 = false;

    F_lung1 = std::pow((std::pow((Square_Points[0].x - Square_Points[1].x),2) + std::pow((Square_Points[0].y - Square_Points[1].y),2)), 0.5);
    F_lung2 = std::pow((std::pow((Square_Points[1].x - Square_Points[2].x),2) + std::pow((Square_Points[1].y - Square_Points[2].y),2)), 0.5);

    if (F_lung2 > F_lung1)
    {..................

but result is the same...

Regards
giorgio

gfxx · 28 Sept 2016, 16:34

@gfxx Ok the function works whithout error ... but I have 0 result value for all variables ....

Regards
giorgio

gfxx · 28 Sept 2016, 17:07

@gfxx mmm.... these type of approach is not desirable in my case ... so at the last I solve my problem wit a specific c++ class with function that return struct result ... if someone had this same problem or wish to create a class with a return statement struct or a void with a return struct placed here the basic steps ....

/*************************FILE.h*********************************/

#ifndef FILE_H
#define FILE_H

#include <QThread> /**** and other magic include ****/
#include <QtCore/QVariant>
.....


struct myFirstStruct{
    cv::Point2f Square_Points[4];
    bool Up1_2Square;
    bool Down1_2Square;
    bool returnValue1;
    bool returnValue2;
    ...... /***other member DECLARE ***/

};



class File
{
public:
    File();

    myFirstStruct myVoid( cv::Point2f Square_Points[4], bool Up1_2Square, bool Down1_2Square);
    struct myFirstStruct MyIstance;

private:


};

#endif // FILE_H

/*************************FILE.cpp*********************************/

#include "File.h"



File::File()
{

}


  myFirstStruct File::myVoid(cv::Point2f Square_Points[4], bool Up1_2Square, bool Down1_2Square)
    {
/***do somethings*****/

MyIstance.returnValue1 = calculatedvalue1;
MyIstance.returnValue2 = calculatedvalue2;

return MyIstance;
}

/*************************InSomeFileOfYourApp.cpp*********************************/

#include "File.h"

int var1; .....

Your::mainOrSub(){

File MyClassIstance;

MyClassIstance.myVoid(cv-point-value, bool-value, bool-value);

yourCalculatedData1 =  myVoid.MyIstance.returnValue1;
yourCalculatedData2 =  myVoid.MyIstance.returnValue2;

.......
}

I hope These Help someone ...
Regards
Giorgio

VRonin · 28 Sept 2016, 20:46

@gfxx Class and Struct are the same thing.

struct MyClass{
// stuff
};
// is the same as:
class MyClass{
public:
// stuff
};

see http://www.cplusplus.com/doc/tutorial/classes/ for a quick overview of how to use classes and structs

gfxx · 29 Sept 2016, 07:16

@VRonin yes struct and class is quite similar .... but not the same things..... I know .. some C programmers not like class and prefer struct .... When I was A good programmer I use me too only struct and no class .... but for now I'm happy class exist .... ;)

regards
Giorgio

VRonin · 29 Sept 2016, 09:05

@gfxx C has no classes. C has only structs and they cannot contain methods, just members. C is not an object oriented language. In C++ they are the same, the only difference is the default access level (public for struct, private for class)

http://www.geeksforgeeks.org/g-fact-76/

C++ struct function with return struct ...

-- MYS.h

-- MYS.cpp

--
MYS.h

--
MYS.cpp