struct question

This is a discussion on struct question within the Windows Programming forums, part of the Platform Specific Boards category; This was taken from Mr. Petzold's book, Programming Windows, pages 87, 88, 89, and 90. All rights reserved. Code: /*----------------------------------------------- ...

  1. #1
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    struct question

    This was taken from Mr. Petzold's book, Programming Windows, pages 87, 88, 89, and 90. All rights reserved.
    Code:
    /*-----------------------------------------------
       SYSMETS.H -- System metrics display structure
      -----------------------------------------------*/
    
    #define NUMLINES ((int) (sizeof sysmetrics / sizeof sysmetrics [0]))
    
    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")
    } ;
    In the struct declaration, he declares three variables: iIndex, szLabel, and szDesc. He initializes the struct with statements like
    Code:
    SM_CMONITORS,            TEXT ("blablabla"),
    In this case, is SM_CMONITORS assigned to szLabel and "blablabla" assigned to szDesc? I think so, but I just want to make sure. My real question is, why isn't SM_CMONITORS assigned to iIndex, for example, if iIndex is the first variable of the struct? Who makes that decision? Does that mean I can only initialize one variable of struct sysmetrics if I wanted to? Thanks.

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    Quote Originally Posted by caduardo21
    In the struct declaration, he declares three variables: iIndex, szLabel, and szDesc. He initializes the struct with statements like
    Code:
    SM_CMONITORS,            TEXT ("blablabla"),
    In this case, is SM_CMONITORS assigned to szLabel and "blablabla" assigned to szDesc? I think so, but I just want to make sure. My real question is, why isn't SM_CMONITORS assigned to iIndex, for example, if iIndex is the first variable of the struct? Who makes that decision? Does that mean I can only initialize one variable of struct sysmetrics if I wanted to? Thanks.
    Full bracing would have made this clearer.
    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_CMONITORS,            TEXT ("SM_CMONITORS"),             
                                  TEXT ("Number of monitors"),
         SM_SAMEDISPLAYFORMAT,    TEXT ("SM_SAMEDISPLAYFORMAT"),     
                                  TEXT ("Same color format flag")
    } ;
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
    Magically delicious LuckY's Avatar
    Join Date
    Oct 2001
    Posts
    856
    I got a little lost in the latter part of your question, but I think you've almost got the idea. sysmetrics is an array of structs and each three values of that very long initialization sets the value for each of the three members for that element in the array. It would be much clearer if it were done this way:
    Code:
    struct {
      int a;
      char *b;
      char *c;
    }
    buncha_stuff[] =
    {
      { SOME_CONSTANT_NUMERIC, "fu", "bar" }, 
      { ..., "...", "..." }, ...
    };
    why isn't SM_CMONITORS assigned to iIndex
    It is. The first element in the array is:
    iIndex ==> SM_CXSCREEN,
    szLabel ==> TEXT ("SM_CXSCREEN"),
    szDesc ==> TEXT ("Screen width in pixels"),

    [edit]I type too slow sometimes.[/edit]

  4. #4
    Registered User
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    Jan 2005
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    I see it now. Thanks both of you. Gotta love Dave's coloring talent, ahaha

  5. #5
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    Hey, what about this line, on page 94:
    Code:
    cxCaps = (tm.tmPitchAndFamily & 1 ? 3 : 2) * cxChar / 2;
    does it mean in plain english that
    Code:
    if(last bit of tm.tmPitchAndFamily == 1)
        3 * cxChar / 2;
    
    else
        2 * cxChar / 2;
    Am I correct? Thanks.

  6. #6
    Registered User
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    California
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    Am I correct?
    yep.

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