need some enlightment

This is a discussion on need some enlightment within the C Programming forums, part of the General Programming Boards category; This is just a simple program.... #include <stdio.h> /* BIT-FIELD CONSTANTS */ /* opaque and show */ #define YES 1 ...

  1. #1
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    need some enlightment

    This is just a simple program....

    #include <stdio.h>

    /* BIT-FIELD CONSTANTS */

    /* opaque and show */

    #define YES 1

    #define NO 0

    /* line styles */

    #define SOLID 0

    #define DOTTED 1

    #define DASHED 2

    /* primary colors */

    #define BLUE 4

    #define GREEN 2

    #define RED 1

    /* mixed colors */

    #define BLACK 0

    #define YELLOW (RED | GREEN)

    #define MAGENTA (RED | BLUE)

    #define CYAN (GREEN | BLUE)

    #define WHITE (RED | GREEN | BLUE)



    /* BITWISE CONSTANTS */

    #define OPAQUE 0x1

    #define FILL_BLUE 0x8

    #define FILL_GREEN 0x4

    #define FILL_RED 0x2

    #define FILL_MASK 0xE

    #define BORDER 0x100

    #define BORDER_BLUE 0x800

    #define BORDER_GREEN 0x400

    #define BORDER_RED 0x200

    #define BORDER_MASK 0xE00

    #define B_SOLID 0

    #define B_DOTTED 0x1000

    #define B_DASHED 0x2000

    #define STYLE_MASK 0x3000

    const char * colors[8] = {"black", "red", "green", "yellow",

    "blue", "magenta", "cyan", "white"};

    struct box_props {

    unsigned int opaque : 1;

    unsigned int fill_color : 3;

    unsigned int : 4;

    unsigned int show_border : 1;

    unsigned int border_color : 3;

    unsigned int border_style : 2;

    unsigned int : 2;

    };



    union Views /* look at data as struct or as unsigned short */

    {

    struct box_props st_view;

    unsigned int ui_view;

    };

    void show_settings(const struct box_props * pb);

    void show_settings1(unsigned short);

    char * itobs(unsigned int n, char * ps);

    int main(void)

    {
    /* create Views object, initialize struct box view */

    union Views box = {{YES, YELLOW , YES, GREEN, DASHED}};

    char bin_str[8 * sizeof(unsigned int) + 1];

    printf("Original box settings:\n");

    show_settings(&box.st_view);

    printf("\nBox settings using unsigned int view:\n");

    show_settings1(box.ui_view);

    printf("bits are %s\n",

    itobs(box.ui_view,bin_str));

    box.ui_view &= ~FILL_MASK; /* clear fill bits */

    box.ui_view |= (FILL_BLUE | FILL_GREEN); /* reset fill */

    box.ui_view ^= OPAQUE; /* toggle opacity */

    box.ui_view |= BORDER_RED; /* wrong approach */

    box.ui_view &= ~STYLE_MASK; /* clear style bits */

    box.ui_view |= B_DOTTED; /* set style to dotted*/

    printf("\nModified box settings:\n");

    show_settings(&box.st_view);

    printf("\nBox settings using unsigned int view:\n");

    show_settings1(box.ui_view);

    printf("bits are %s\n",

    itobs(box.ui_view,bin_str));

    return 0;

    }

    void show_settings(const struct box_props * pb)

    {

    printf("Box is %s.\n",

    pb->opaque == YES? "opaque": "transparent");

    printf("The fill color is %s.\n", colors[pb->fill_color]);

    printf("Border %s.\n",

    pb->show_border == YES? "shown" : "not shown");

    printf("The border color is %s.\n", colors[pb->border_color]);

    printf ("The border style is ");

    switch(pb->border_style)

    {

    case SOLID : printf("solid.\n"); break;

    case DOTTED : printf("dotted.\n"); break;

    case DASHED : printf("dashed.\n"); break;

    default : printf("unknown type.\n");

    }

    }

    void show_settings1(unsigned short us)

    {

    printf("box is %s.\n",

    us & OPAQUE == OPAQUE? "opaque": "transparent");

    printf("The fill color is %s.\n",

    colors[(us >> 1) & 07]);

    printf("Border %s.\n",

    us & BORDER == BORDER? "shown" : "not shown");

    printf ("The border style is ");

    switch(us & STYLE_MASK)

    {

    case B_SOLID : printf("solid.\n"); break;

    case B_DOTTED : printf("dotted.\n"); break;

    case B_DASHED : printf("dashed.\n"); break;

    default : printf("unknown type.\n");

    }

    printf("The border color is %s.\n",

    colors[(us >> 9) & 07]);

    }

    /* convert int to binary string */

    char * itobs(unsigned int n, char * ps)

    {

    int i;

    static int size = 8 * sizeof(unsigned int);

    for (i = size - 1; i >= 0; i--, n >>= 1)

    ps[i] = (01 & n) + '0';

    ps[size] = '\0';

    return ps;

    }



    my question about that is that the line....
    Code:
    union Views box = {{YES, YELLOW , YES, GREEN, DASHED}};
    for my understanding about this line....it only initialize the structure in the union....
    because of these brackets {{}} because it only initialize the first variables in the union and that is the structure....my question is, how the
    Code:
    unsigned int  ui_view;
    get those values??
    thanks in advance....

  2. #2

  3. #3
    Kernel hacker
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    Farncombe, Surrey, England
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    Quote Originally Posted by sick View Post
    my question about that is that the line....
    Code:
    union Views box = {{YES, YELLOW , YES, GREEN, DASHED}};
    for my understanding about this line....it only initialize the structure in the union....
    because of these brackets {{}} because it only initialize the first variables in the union and that is the structure....my question is, how the
    Code:
    unsigned int  ui_view;
    get those values??
    thanks in advance....
    It holds the same address as struct box_props, which means that the bit fields set in struct box_props will overlay into the ui_view value. How those bitfields map into a 16 or 32-bit integer, I can't really say, since the standard for how bitfields are stored is entirely up to the compiler.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  4. #4
    Registered User
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    Sep 2008
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    thanks for that mats...but could you clarify some point...please forgive my noobness....umm you say that it holds the same address....umm could you use some examples to give me some idea? thanks mats...

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