How to return a struct from a class in C++?

Question

I have a problem in returning a struct from a method declared in a class. The struct i is composed by 3 integers: day, month and year. I set these three values using a method in the class.

struct dmy{
   int day, month, year;
};
dmy c;

Then I have a method to return the full struct

dmy Date::getS(){
  return c;
}

But I get lots of errors in compiling. What should I do?

I've also read Is it safe to return a struct in C or C++? but I haven't solved my issue.

The program is composed from main.cpp, Difference.h and Date.h

Errors in Date.h :

[Error] 'dmy' does not name a type

Main

using namespace std;

#include <iostream>
#include "Date.h"

int main(int argc, char** argv) {

    Date date1;
    Date date2;

    cout<<"Insert first date\n";
    date1.setAll();

    return 0;
}

Date.h

class Date{
public:
    Date(){
    }
    ~Date(){
    }
    void setAll();
    struct dmy{
        int day, month, year;
    };
    dmy c;
    dmy getS();
private:
    void setDay();
    void setMonth();
    void setYear();
};

void Date::setAll(){
    setDay();
    setMonth();
    setYear();
}

void Date::setDay(){
    do{
        cout<<"Type day: ";
        cin>>c.day;
    }while(0<c.day<31);
}

void Date::setMonth(){
    //didn't right the checking again
    cout<<"Type month: ";
    cin>>c.month;
}

void Date::setYear(){
    cout<<"Type year: ";
    cin>>c.year;
}

dmy Date::getS(){
    return c;
}

NOTE: The struct was called 'i'

Show your errors. To an experienced eye, the error tells exactly what is wrong and how it might be fixed. — Joseph Mansfield, Jan 23 '14 at 11:53
Ok, I am writing from my tablet unfortunatelly, so it's not so easy. At school we don't have internet access. — Mitro, Jan 23 '14 at 11:55
Do you declare `struct i` in a header file? Do you include that header file? — Benoit, Jan 23 '14 at 12:05
Yes, I included the header file in main, but not in Differece. Should I do so? — Mitro, Jan 23 '14 at 12:10
@AlessioMTX: You'll need to declare `struct i;` (or include the header if you need the full definition) in every file that uses it. — Mike Seymour, Jan 23 '14 at 12:14
Also, you probably shouldn't name your struct *i*. *i* is often used as a variable name. — dsi, Jan 23 '14 at 12:14

Ben Crowhurst · Answer 1 · 2014-01-23T12:36:43.587

Example

#include <cstdio>
#include <cstdlib>

struct DateInfo {
   int day;
   int month;
   int year;
};

class Date {
 public:
   Date(const int day, const int month, const int year) : m_info( { day, month, year } )
   {
      //n/a
   }

   DateInfo get_info( void ) const
   {
     return m_info;
   }

 private:
   DateInfo m_info;
};

int main( int, char** )
{
   Date date( 29, 02, 1984 );

   DateInfo info = date.get_info( );

   printf( "%i\n", info.year );

   return EXIT_SUCCESS;
}

Build

g++ -std=c++11 -o date date.cpp

score 1 · Accepted Answer · answered Jan 23 '14 at 14:36

1

instead of

dmy Date::getS(){
    return c;
}

write

Date::dmy Date::getS(){
    return c;
}

since "dmy" is not in the global namespace.

answered Jan 23 '14 at 14:36

AndersK

35,813
6
60
86

That would be true if dmy was a nested class. But is not – Davidbrcz Jan 23 '14 at 14:45

score 0 · Answer 3 · answered Jan 23 '14 at 12:15

0

Try this:

class C1
 {
public:
 struct S1
  {
  int a,b,c;
  };

 S1 f1() { S1 s; return s; }
 };

void main()
 {
 C1 c;
 C1::S1 s;

 s=c.f1();
 }

C1 - class
C1::S1 - struct inside class C1
C1::f1 - function returning C1::S1

answered Jan 23 '14 at 12:15

Spektre

49,595
11
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380

Embedding the structures definition within the class can cause problems with compile time dependencies. If you alter the S1 structure all those including the C1 header will need to be recompiled. Benefits can come from extracting the structure and forward declaring it when needed. see Compilation Firewall http://c2.com/cgi/wiki?PimplIdiom – Ben Crowhurst Jan 23 '14 at 12:40

score 0 · Answer 4 · answered Jan 23 '14 at 12:40

0

I doubt that your source code is compiled in the C style other that C++ style. You could try to change the file extension to ".cpp" instead of ".c" and then gcc will do it's job in C++ style.

answered Jan 23 '14 at 12:40

faraday

41
3

How to return a struct from a class in C++?

4 Answers4