C++ Classes
Results 1 to 4 of 4

Thread: C++ Classes

  1. #1
    Member
    Join Date
    Feb 2003
    Posts
    78

    C++ Classes

    Ok, I am a little confused as to why this is not working. The code I am going to post is all I have right now, but it is part of a larger program I plan to build. I cant get started on my larger project until I finish my class header file. The only problem is, I cant get my class to work correctly. It worked almost perfect...until I made made the class have private variables and public functions. I know you are supposed to do this, but I cant seem to get it to work.

    Code:
    //Class Music
    #include<iostream>
    class m
    {
        public:
        
        void SetGroup(char[]);
        char Get();
        
        private:
        char group[50];
        struct cds
        {
            char title[];
            struct songs 
            {
                    char songName[];
                    char lyrics[];
            };
            songs song[25];
        };
        
        cds cd[50];   
    };
    void m::SetGroup(char igroup[])
    {
        group[50] = igroup[50];
        std::cout<<igroup<<'\n'<<group;
    }
    char m::Get()
    {
        return group[50];
    }
    
    int main()
    {
        m music[3];
        char hey[] = "Senses Fail";
        music[0].SetGroup(hey);
      //  std::cout<<music[0].Get();
        
        system("PAUSE");
        return 0;    
    }
    And the output looks like:

    Senses Fail
    ╨ⁿ"Press any key to continue . . .

    I am confused as to why the value is passed, but not assigned to the class variable. Because I havent gotten this part to work, I havent worried about the Get function. I already see a problem. Can I return a char array? Would char m::Get() return a char array, because I tryed it with char[] m::Get() and that didnt work, so I am a little confused as to what to to about that. But I am not really there yet. I cant even assign the class variable the right value.
    Thanks for any help provided.

    -Ep
    01001001001000000100110001101111011101100110010100100000010000100110010101110100011101000111100100100001

  2. #2
    Member
    Join Date
    Feb 2003
    Posts
    78
    Well, no one has replied yet. Someone else has helped me...kinda. He send me this code, but has yet to explain what it all does. He made changes and I was wondering if anyone could explain why he changed what he did. Or, tell me how you would change the code to make it work for you and why.

    Code:
    //Class Music 
    
    #include <iostream> 
    #include <string> 
    
    struct songs 
    { 
       std::string songName; 
        std::string lyrics; 
    }; 
    
    struct cds 
    { 
        std::string title; 
        songs song[25]; 
    }; 
    
    class m 
    { 
       public: 
          void SetGroup(char*); 
          char* Get();    
        private: 
          std::string group;    
          cds cd[50];    
    }; 
    
    void m::SetGroup(char* igroup) 
    { 
        group = igroup; 
        std::cout << igroup << '\n' << group.c_str(); 
    } 
    
    char* m::Get() 
    { 
        return group.c_str(); 
    } 
    
    int main() 
    { 
        m music[3]; 
        char* hey = "Senses Fail"; 
        music[0].SetGroup(hey); 
       std::cout << music[0].Get(); 
       std::cin.get(); 
        return 0;    
    }
    Waiting for any response...
    -Ep
    01001001001000000100110001101111011101100110010100100000010000100110010101110100011101000111100100100001

  3. #3
    Member
    Join Date
    Feb 2003
    Posts
    78
    Well, No one has yet to reply. Im not sure if that is because everyone that has looked at my post sofar has no idea what I am talking about, or dont know how to fix it, but yeah. Anywayz, So far so good. I have fixed all of the problems sofar.

    Code:
    //Lyrics
    //Class Music 
    
    #include <iostream> 
    #include <string> 
    using namespace std;
    
    struct songs 
    { 
        string songName; 
        string lyrics; 
    }; 
    
    struct cds 
    { 
        string title; 
        songs song[25]; 
    }; 
    
    class m 
    { 
       public: 
          void SetGroup(string); 
          string GetGroup();
          void SetTitle(string, int);
          string GetTitle(int);
       private: 
          string group;    
          cds cd[5];    
    }; 
    
    void m::SetGroup(string xgroup) 
    { 
        group = xgroup;
    } 
    
    string m::GetGroup() 
    { 
        return group; 
    }
    void m::SetTitle(string xtitle, int cnum)
    {
        cd[cnum].title = xtitle;
    }
    string m::GetTitle(int cnum)
    {
        return cd[cnum].title;
    }
    
    int main() 
    { 
        m music[3]; 
        char hey[256];
        cin.get(hey,256); 
        music[0].SetGroup(hey);
        cin.ignore(1,'\n');
        cin.get(hey,256); 
        music[0].SetTitle(hey, 0);
        cout<<music[0].GetGroup()<<'\n'<<music[0].GetTitle(0)<<endl;
         
        system("PAUSE"); 
        return 0;    
    }
    Just incase anyone was following the code and wanted to know why it wasnt working, I will explain it to the best of my knowledge. My "friend" had the GetGroup() functions returning a char pointer. Well, I re-read a chapter on pointers, which didnt help at all, and then I did some research on teh internet.
    First, when you declare a char pointer, it is a little different then normal pointers.

    Code:
    #include <iostream> 
    #include <string> 
    using namespace std;
    
    int main()
    {
        string word = "Hey";
        char* pChar = "Rah";
        cout<<&word<<'\n'<<pChar<<'\n'<<word<<'\n'<<*pChar<<endl;
    
        int num = 0;
        int* pInt;
        *pInt = 1;
        cout<<&num<<'\n'<<pInt<<'\n'<<num<<'\n'<<*pInt<<endl;
    
        system("PAUSE");
        return 0;    
    }
    Ouput:
    0x22ff58
    Rah
    Hey
    R
    0x22ff40
    0x22ffe0
    0
    1
    Press any key to continue . . .

    With the int pointer, it contains the address which points to a value. With the char pointer, (to my knowledge) it also contains an address which points to a value. But like it says, it is a char, which only holds one character. So when I assigned char* pChar = "Rah"; it gave the first address of the pointer R. If you want to access the a, you would have to do something like *(pChar+1). I know this is confusing, because I am still a little confused myself. If all char pointers are const, and you cant access the full string which the char pointer points to, what good are they. I dont know and hope someone answers this question.
    Anywayz, I hope I helped someone out with my code, and I hope someone helps me out with my above question. Thanks for following along.
    -Ep
    01001001001000000100110001101111011101100110010100100000010000100110010101110100011101000111100100100001

  4. #4
    Senior Member
    Join Date
    Mar 2004
    Posts
    557
    Hi


    Pointers are confusing, no question about that. However, I try to shed some light on that
    issue for you, but I will be rather technical
    Code:
        char* pChar = "abcdef";
    First notion:
    What is pChar? pChar is not a "char", which holds only one character, but it is a
    "char[4]" - buffer, that contains the address of "abcdef".
    Test:
    Code:
        printf("The size of the pChar itself: %d\n", sizeof(pChar));
           // the output is 4, not 6 or 1.

    Second notion:
    The address of pChar itself is more or less irrelevant (here):
    Code:
        printf("The address of the pChar itself (on the stack!): %x\n",&pChar);

    Third notion:
    At the address of pChar itself however, there are 4 bytes, which are the address
    of "abcdef".
    Code:
     	printf("The content of the pChar itself: %x\n",pChar);
    Note, that this address actually is not on the stack but in the .data-section
    of your executable, that is also in the memory.

    Fourth notion:
    At that memory address, there is "abcdef".
    Code:
    	printf("The content at the memory address %x stored in pChar: %s\n",pChar,pChar);
    Final notion:
    Often, you want to access one particular char in your array. You can do this
    in two ways, which are completely equivalent!
    Code:
       printf("%c",pChar[1]);   // the second element of "abcdef" = 'b'
       printf("%c",*pChar+1); 
       printf("%c",*(pChar+1)); 
            // also the second element: Take the address stored in pChar, which is the address
            // of "abcdef" and increase that one by one. The address of "abcdef" actually
            // is the beginning of it, ie 'a'. The following char in the memory is thus 'b'

    Cheers
    If the only tool you have is a hammer, you tend to see every problem as a nail.
    (Abraham Maslow, Psychologist, 1908-70)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

 Security News

     Patches

       Security Trends

         How-To

           Buying Guides