Programming Forums > Application Development > C

JawaKing00 · May 31st, 2006, 1:00 PM

I am writing some code that will display a bitmap image to a display. The bitmap is stored as a very large constant array of bytes. I want to write a function that I can pass the pointer to the array to and have the function write it to the display. Currently, though, I am getting a compiler warning saying "passing arg 1 of `DisplayGraphicScreen' discards qualifiers from pointer target type"

Here is what I have:

in main.c

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void main (void)
{
    //stuff

    DisplayGraphicScreen(logo1, sizeof(logo1));

    //more stuff
}

The function

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VOID DisplayGraphicScreen ( INT8U *MyScreen, INT16U ArraySize )
{
    INT8U i;

    DisplayChar(0x1F);
    DisplayChar(0x28);
    DisplayChar(0x66);
    DisplayChar(0x11);

    for (i=0; i < ArraySize; i++)
    {
        DisplayChar(MyScreen[i]);
    }
}

The array

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const INT8U logo1[4101]= 
{
    0x00, 
    0x01, 
    0x10, 
    0x00, 
    0x01, 
    // a ton more entries
};

When I use the code that is in the function by itself, it displays fine. But when I try to pass the array to the function I get that compiler warning and a bunch of garbage on the screen. Is there something I am doing wrong passing that array to the function?

Any help would be greatly appreciated.

Thanks,

Andy

Adak · May 31st, 2006, 1:33 PM

I don't understand why you don't just pass the array's base address (the array name itself), to the function?

Adak

Narue · May 31st, 2006, 1:44 PM

>void main (void)
main returns int.

>VOID DisplayGraphicScreen ( INT8U *MyScreen, INT16U ArraySize )
logo1 is defined as an array of const data, but you're passing it as if it were not const. That's generally not a good idea:

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VOID DisplayGraphicScreen ( const INT8U *MyScreen, INT16U ArraySize )

JawaKing00 · May 31st, 2006, 2:10 PM

Thanks I'll try that out. I figured it would be something dumb like that.

JawaKing00 · May 31st, 2006, 2:19 PM

Ok I knew it was going to be something stupid.

The index variable for the FOR loop is declared as an INT8U, and the value it's compared against is an INT16U, and that is rarely less than 255, so the FOR statement was always true and only getting the first 255 entries in the array.

I changed i to a 16 bit variable, and now things work great.

Thanks for the input.

May 31st, 2006, 1:00 PM	#1
JawaKing00 Newbie Join Date: Sep 2004 Posts: 29 Rep Power: 0	Arrays, Pointers, and Constants I am writing some code that will display a bitmap image to a display. The bitmap is stored as a very large constant array of bytes. I want to write a function that I can pass the pointer to the array to and have the function write it to the display. Currently, though, I am getting a compiler warning saying "passing arg 1 of `DisplayGraphicScreen' discards qualifiers from pointer target type" Here is what I have: in main.c (Toggle Plain Text) void main (void) { //stuff DisplayGraphicScreen(logo1, sizeof(logo1)); //more stuff } void main (void) { //stuff DisplayGraphicScreen(logo1, sizeof(logo1)); //more stuff } The function (Toggle Plain Text) VOID DisplayGraphicScreen ( INT8U MyScreen, INT16U ArraySize ) { INT8U i; DisplayChar(0x1F); DisplayChar(0x28); DisplayChar(0x66); DisplayChar(0x11); for (i=0; i < ArraySize; i++) { DisplayChar(MyScreen[i]); } } VOID DisplayGraphicScreen ( INT8U MyScreen, INT16U ArraySize ) { INT8U i; DisplayChar(0x1F); DisplayChar(0x28); DisplayChar(0x66); DisplayChar(0x11); for (i=0; i < ArraySize; i++) { DisplayChar(MyScreen[i]); } } The array (Toggle Plain Text) const INT8U logo1[4101]= { 0x00, 0x01, 0x10, 0x00, 0x01, // a ton more entries }; const INT8U logo1[4101]= { 0x00, 0x01, 0x10, 0x00, 0x01, // a ton more entries }; When I use the code that is in the function by itself, it displays fine. But when I try to pass the array to the function I get that compiler warning and a bunch of garbage on the screen. Is there something I am doing wrong passing that array to the function? Any help would be greatly appreciated. Thanks, Andy

May 31st, 2006, 1:44 PM	#3
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	>void main (void) main returns int. >VOID DisplayGraphicScreen ( INT8U MyScreen, INT16U ArraySize ) logo1 is defined as an array of const data, but you're passing it as if it were not const. That's generally not a good idea: (Toggle Plain Text) VOID DisplayGraphicScreen ( const INT8U MyScreen, INT16U ArraySize ) VOID DisplayGraphicScreen ( const INT8U *MyScreen, INT16U ArraySize ) __________________ Even if the voices aren't real, they have some pretty good ideas.

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May 31st, 2006, 1:33 PM	#2
Adak Hobby Coder Join Date: May 2006 Posts: 59 Rep Power: 0	I don't understand why you don't just pass the array's base address (the array name itself), to the function? Adak

May 31st, 2006, 2:10 PM	#4
JawaKing00 Newbie Join Date: Sep 2004 Posts: 29 Rep Power: 0	Thanks I'll try that out. I figured it would be something dumb like that.

May 31st, 2006, 2:19 PM	#5
JawaKing00 Newbie Join Date: Sep 2004 Posts: 29 Rep Power: 0	Ok I knew it was going to be something stupid. The index variable for the FOR loop is declared as an INT8U, and the value it's compared against is an INT16U, and that is rarely less than 255, so the FOR statement was always true and only getting the first 255 entries in the array. I changed i to a 16 bit variable, and now things work great. Thanks for the input.

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Arrays, Pointers, and Constants