Ok, Structs, I need help I am not familiar with them

Ok so I've read a book on C++ and whatnot, but it didn't really say what a struct was, it just mentioned that it was a cousin of a class and some other stuff. Now that I am reading Petzold's book, which uses C not C++ I've stumbled upon the following header file..............

Code:

---

struct
{
    int    iIndex ;
    TCHAR * szLabel ;
    TCHAR * szDesc ;
}
sysmetrics [] =
{
    SM_CXSCREEN,            TEXT ("SM_CXSCREEN"),             
                              TEXT ("Screen width in pixels"),
    SM_CYSCREEN,            TEXT ("SM_CYSCREEN"),             
                              TEXT ("Screen height in pixels"),
    SM_CXVSCROLL,            TEXT ("SM_CXVSCROLL"),           
                              TEXT ("Vertical scroll width"),
    SM_CYHSCROLL,            TEXT ("SM_CYHSCROLL"),           
                              TEXT ("Horizontal scroll height"),
    SM_CYCAPTION,            TEXT ("SM_CYCAPTION"),           
                              TEXT ("Caption bar height"),
    SM_CXBORDER,            TEXT ("SM_CXBORDER"),             
                              TEXT ("Window border width"),
    SM_CYBORDER,            TEXT ("SM_CYBORDER"),             
                              TEXT ("Window border height"),
    SM_CXFIXEDFRAME,        TEXT ("SM_CXFIXEDFRAME"),         
                              TEXT ("Dialog window frame width"),
    SM_CYFIXEDFRAME,        TEXT ("SM_CYFIXEDFRAME"),         
                              TEXT ("Dialog window frame height"),
    SM_CYVTHUMB,            TEXT ("SM_CYVTHUMB"),             
                              TEXT ("Vertical scroll thumb height"),
    SM_CXHTHUMB,            TEXT ("SM_CXHTHUMB"),             
                              TEXT ("Horizontal scroll thumb width"),
    SM_CXICON,              TEXT ("SM_CXICON"),               
                              TEXT ("Icon width"),
    SM_CYICON,              TEXT ("SM_CYICON"),               
                              TEXT ("Icon height"),
    SM_CXCURSOR,            TEXT ("SM_CXCURSOR"),             
                              TEXT ("Cursor width"),
    SM_CYCURSOR,            TEXT ("SM_CYCURSOR"),             
                              TEXT ("Cursor height"),
    SM_CYMENU,              TEXT ("SM_CYMENU"),               
                              TEXT ("Menu bar height"),
    SM_CXFULLSCREEN,        TEXT ("SM_CXFULLSCREEN"),         
                              TEXT ("Full screen client area width"),
    SM_CYFULLSCREEN,        TEXT ("SM_CYFULLSCREEN"),         
                              TEXT ("Full screen client area height"),
    SM_CYKANJIWINDOW,        TEXT ("SM_CYKANJIWINDOW"),       
                              TEXT ("Kanji window height"),
    SM_MOUSEPRESENT,        TEXT ("SM_MOUSEPRESENT"),         
                              TEXT ("Mouse present flag"),
    SM_CYVSCROLL,            TEXT ("SM_CYVSCROLL"),           
                              TEXT ("Vertical scroll arrow height"),
    SM_CXHSCROLL,            TEXT ("SM_CXHSCROLL"),           
                              TEXT ("Horizontal scroll arrow width"),
    SM_DEBUG,                TEXT ("SM_DEBUG"),               
                              TEXT ("Debug version flag"),
    SM_SWAPBUTTON,          TEXT ("SM_SWAPBUTTON"),           
                              TEXT ("Mouse buttons swapped flag"),
    SM_CXMIN,                TEXT ("SM_CXMIN"),               
                              TEXT ("Minimum window width"),
    SM_CYMIN,                TEXT ("SM_CYMIN"),               
                              TEXT ("Minimum window height"),
    SM_CXSIZE,              TEXT ("SM_CXSIZE"),               
                              TEXT ("Min/Max/Close button width"),
    SM_CYSIZE,              TEXT ("SM_CYSIZE"),               
                              TEXT ("Min/Max/Close button height"),
    SM_CXSIZEFRAME,          TEXT ("SM_CXSIZEFRAME"),         
                              TEXT ("Window sizing frame width"),
    SM_CYSIZEFRAME,          TEXT ("SM_CYSIZEFRAME"),         
                              TEXT ("Window sizing frame height"),
    SM_CXMINTRACK,          TEXT ("SM_CXMINTRACK"),           
                              TEXT ("Minimum window tracking width"),
    SM_CYMINTRACK,          TEXT ("SM_CYMINTRACK"),           
                              TEXT ("Minimum window tracking height"),
    SM_CXDOUBLECLK,          TEXT ("SM_CXDOUBLECLK"),         
                              TEXT ("Double click x tolerance"),
    SM_CYDOUBLECLK,          TEXT ("SM_CYDOUBLECLK"),         
                              TEXT ("Double click y tolerance"),
    SM_CXICONSPACING,        TEXT ("SM_CXICONSPACING"),       
                              TEXT ("Horizontal icon spacing"),
    SM_CYICONSPACING,        TEXT ("SM_CYICONSPACING"),       
                              TEXT ("Vertical icon spacing"),
    SM_MENUDROPALIGNMENT,    TEXT ("SM_MENUDROPALIGNMENT"),   
                              TEXT ("Left or right menu drop"),
    SM_PENWINDOWS,          TEXT ("SM_PENWINDOWS"),           
                              TEXT ("Pen extensions installed"),
    SM_DBCSENABLED,          TEXT ("SM_DBCSENABLED"),         
                              TEXT ("Double-Byte Char Set enabled"),
    SM_CMOUSEBUTTONS,        TEXT ("SM_CMOUSEBUTTONS"),       
                              TEXT ("Number of mouse buttons"),
    SM_SECURE,              TEXT ("SM_SECURE"),               
                              TEXT ("Security present flag"),
    SM_CXEDGE,              TEXT ("SM_CXEDGE"),               
                              TEXT ("3-D border width"),
    SM_CYEDGE,              TEXT ("SM_CYEDGE"),               
                              TEXT ("3-D border height"),
    SM_CXMINSPACING,        TEXT ("SM_CXMINSPACING"),         
                              TEXT ("Minimized window spacing width"),
    SM_CYMINSPACING,        TEXT ("SM_CYMINSPACING"),         
                              TEXT ("Minimized window spacing height"),
    SM_CXSMICON,            TEXT ("SM_CXSMICON"),             
                              TEXT ("Small icon width"),
    SM_CYSMICON,            TEXT ("SM_CYSMICON"),             
                              TEXT ("Small icon height"),
    SM_CYSMCAPTION,          TEXT ("SM_CYSMCAPTION"),         
                              TEXT ("Small caption height"),
    SM_CXSMSIZE,            TEXT ("SM_CXSMSIZE"),             
                              TEXT ("Small caption button width"),
    SM_CYSMSIZE,            TEXT ("SM_CYSMSIZE"),             
                              TEXT ("Small caption button height"),
    SM_CXMENUSIZE,          TEXT ("SM_CXMENUSIZE"),           
                              TEXT ("Menu bar button width"),
    SM_CYMENUSIZE,          TEXT ("SM_CYMENUSIZE"),           
                              TEXT ("Menu bar button height"),
    SM_ARRANGE,              TEXT ("SM_ARRANGE"),             
                              TEXT ("How minimized windows arranged"),
    SM_CXMINIMIZED,          TEXT ("SM_CXMINIMIZED"),         
                              TEXT ("Minimized window width"),
    SM_CYMINIMIZED,          TEXT ("SM_CYMINIMIZED"),         
                              TEXT ("Minimized window height"),
    SM_CXMAXTRACK,          TEXT ("SM_CXMAXTRACK"),           
                              TEXT ("Maximum draggable width"),
    SM_CYMAXTRACK,          TEXT ("SM_CYMAXTRACK"),           
                              TEXT ("Maximum draggable height"),
    SM_CXMAXIMIZED,          TEXT ("SM_CXMAXIMIZED"),         
                              TEXT ("Width of maximized window"),
    SM_CYMAXIMIZED,          TEXT ("SM_CYMAXIMIZED"),         
                              TEXT ("Height of maximized window"),
    SM_NETWORK,              TEXT ("SM_NETWORK"),             
                              TEXT ("Network present flag"),
    SM_CLEANBOOT,            TEXT ("SM_CLEANBOOT"),           
                              TEXT ("How system was booted"),
    SM_CXDRAG,              TEXT ("SM_CXDRAG"),               
                              TEXT ("Avoid drag x tolerance"),
    SM_CYDRAG,              TEXT ("SM_CYDRAG"),               
                              TEXT ("Avoid drag y tolerance"),
    SM_SHOWSOUNDS,          TEXT ("SM_SHOWSOUNDS"),           
                              TEXT ("Present sounds visually"),
    SM_CXMENUCHECK,          TEXT ("SM_CXMENUCHECK"),         
                              TEXT ("Menu check-mark width"),
    SM_CYMENUCHECK,          TEXT ("SM_CYMENUCHECK"),         
                              TEXT ("Menu check-mark height"),
    SM_SLOWMACHINE,          TEXT ("SM_SLOWMACHINE"),         
                              TEXT ("Slow processor flag"),
    SM_MIDEASTENABLED,      TEXT ("SM_MIDEASTENABLED"),       
                              TEXT ("Hebrew and Arabic enabled flag"),
    SM_MOUSEWHEELPRESENT,    TEXT ("SM_MOUSEWHEELPRESENT"),   
                              TEXT ("Mouse wheel present flag"),
    SM_XVIRTUALSCREEN,      TEXT ("SM_XVIRTUALSCREEN"),       
                              TEXT ("Virtual screen x origin"),
    SM_YVIRTUALSCREEN,      TEXT ("SM_YVIRTUALSCREEN"),       
                              TEXT ("Virtual screen y origin"),
    SM_CXVIRTUALSCREEN,      TEXT ("SM_CXVIRTUALSCREEN"),     
                              TEXT ("Virtual screen width"),
    SM_CYVIRTUALSCREEN,      TEXT ("SM_CYVIRTUALSCREEN"),     
                              TEXT ("Virtual screen height"),
    SM_CMONITORS,            TEXT ("SM_CMONITORS"),           
                              TEXT ("Number of monitors"),
    SM_SAMEDISPLAYFORMAT,    TEXT ("SM_SAMEDISPLAYFORMAT"),   
                              TEXT ("Same color format flag")
} ;

---

So please how does this thing work...........and how are

int iIndex ;
TCHAR * szLabel ;
TCHAR * szDesc ;

related to Systemetrics.......
As some of you know I started C++ not a long time ago.......SO PLEASE NO FLAMING THE NEWBIES!!!!!!!!! :D :D :p :p

PS I know very little about C..........

Just glancing over it I can deduce the following. The member iIndex is an offset into the array of descriptions and labels. The 2 pointers are to the actual Label and Description. So, I'm not sure what exactly you are asking or if that answered anything? Structs are similiar to classes (kind of) but one important difference is that all of the struct data members are public. Any specific questions, just shoot.

c++ structs are just like classes (except always public.)

a C struct is different. the struct you posted makes a struct with the elements iIndex, szLabel, and szDesc, whose array is named sysmetrics. from there on the various elements are being initialized. to make it easier i'll post a similar example:

Code:

---

char x[6] = {'t','r','e','e','s',0};

---

you see the resemblance?

A structure is a group of variables bundled by a common name. Consider:

Code:

---

struct vehicle {
    char *name;
    int wheels;
    float milesPerGallon;
};

---

There. You have a vehicle. You can name your vehicle. You can give it different numbers of wheels, and you can give it a miles per gallon.

Let's say we want to make a whole list of cars at once. We will create an array of vehicles.

Code:

---

struct vehicles cars[] =
{
    { "Sports Car", 4, 25.5 },
    { "Family Car", 4, 30.1 },
    { "Semi Trailer", 18, 11.7 },
    { "Motorcycle", 2, 40.3 },
    { "Econo-Car", 4, 55.9 }
};

---

There you go. You have a bunch of vehicles. They're all defined.

You can simplify this process by defining the structure and creating the array all in one shot:

Code:

---

struct vehicle {
    char *name;
    int wheels;
    float milesPerGallon;
} vehicles[] =
{
    { "Sports Car", 4, 25.5 },
    { "Family Car", 4, 30.1 },
    { "Semi Trailer", 18, 11.7 },
    { "Motorcycle", 2, 40.3 },
    { "Econo-Car", 4, 55.9 }
};

---

See?

[edit]
Ah. Took too long replying.
[/edit]

Quzah.

Quote:

---

Originally posted by quzah
A structure is a group of variables bundled by a common name. Consider:

Code:

---

struct vehicle {
    char *name;
    int wheels;
    float milesPerGallon;
};

---

There. You have a vehicle. You can name your vehicle. You can give it different numbers of wheels, and you can give it a miles per gallon.

Let's say we want to make a whole list of cars at once. We will create an array of vehicles.

Code:

---

struct vehicles cars[] =
{
    { "Sports Car", 4, 25.5 },
    { "Family Car", 4, 30.1 },
    { "Semi Trailer", 18, 11.7 },
    { "Motorcycle", 2, 40.3 },
    { "Econo-Car", 4, 55.9 }
};

---

There you go. You have a bunch of vehicles. They're all defined.

You can simplify this process by defining the structure and creating the array all in one shot:

Code:

---

struct vehicle {
    char *name;
    int wheels;
    float milesPerGallon;
} vehicles[] =
{
    { "Sports Car", 4, 25.5 },
    { "Family Car", 4, 30.1 },
    { "Semi Trailer", 18, 11.7 },
    { "Motorcycle", 2, 40.3 },
    { "Econo-Car", 4, 55.9 }
};

---

See?

[edit]
Ah. Took too long replying.
[/edit]

Quzah.

---

oh Thank you guys.........you've all been a big help, how would I access an instance of a car with this?

printf("Vehicle %d is:\n\tName: %s\n\tWheel count: %d\n\tMiles Per Gallon: %f\n", vehicle[x].name, vehicle[x].wheels, vehicle[x].milesPerGallon );

Just like you would any other array. When accessing the members of a structure directly, you use the '.' operator:

struct vehicle myCar;

myCar.wheels = 4;
myCar.milesPerGallon = 30.1;

Then of course, since I used a pointer, you'd malloc some space for the name and copy a name into it.

Quzah.

Ok I see where

TCHAR * szLabel ;
TCHAR * szDesc ;


Come in.........first the szLabel and then the szDesc accordingly but I don't see where int iIndex ; comes in..........

btw this is how the program is accessing the array or whatever this is :D

Code:

---


    case WM_PAINT :
          hdc = BeginPaint (hwnd, &ps) ;

          for (i = 0 ; i < NUMLINES ; i++)
          {
              TextOut (hdc, 0, cyChar * i,                     
                        sysmetrics[i].szLabel,
                        lstrlen (sysmetrics[i].szLabel)) ;

              TextOut (hdc, 22 * cxCaps, cyChar * i,     
                        sysmetrics[i].szDesc,
                        lstrlen (sysmetrics[i].szDesc)) ;

              SetTextAlign (hdc, TA_RIGHT | TA_TOP) ;

              TextOut (hdc, 22 * cxCaps + 40 * cxChar, cyChar * i, szBuffer,
                        wsprintf (szBuffer, TEXT ("%5d"),
                            GetSystemMetrics (sysmetrics[i].iIndex))) ;

              SetTextAlign (hdc, TA_LEFT | TA_TOP) ;
          }

---

Never mind I got it thanks.