Dynamically allocating 3D array

This is a discussion on Dynamically allocating 3D array within the C Programming forums, part of the General Programming Boards category; Hi, Am I doing this right? the following code is suppose to allocate memory of type GLubyte which used to ...

  1. #1
    Registered User ssharish2005's Avatar
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    Dynamically allocating 3D array

    Hi, Am I doing this right? the following code is suppose to allocate memory of type GLubyte which used to hold all the values which are read from ppm file. But for some reason the image donst get displayed i suspect that I am not allocating the memory properly. Just to clarify is there any problem with the way I am allocating 3D array. Any comments on this code would be appreciated as well

    Code:
    int AllocateMemory( void )
    {
        unsigned int Count, Count1;
        
        if( ( IndiaMapPPM = malloc( sizeof(GLubyte **) * Width ) ) != NULL )
        {
            for( Count = 0; Count < Width; Count++ )
            {
                 if( ( IndiaMapPPM[Count] = malloc( sizeof( GLubyte *) * Height ) ) != NULL )
                 {
                     for( Count1 = 0; Count1 < Height; Count1++ )
                     {
                          if( ( IndiaMapPPM[Count][Count1] = malloc( sizeof(GLubyte) * RGB ) ) == NULL)
                          {
                              printf("Error: Malloc failed\n");
                              return 1;
                          }
                     }
                 }
                 else
                 { 
                     printf("Error: Malloc failed\n");
                     return 1;
                 }
            }
        }
        else
        {
            printf("Error: Malloc failed\n");
            return 1;
        }
        return 0;
    }
    Thank you

    ssharish

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    There's a global GLubyte ***IndiaMapPPM and success is when AllocateMemory() returns 0?
    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
    Registered User ssharish2005's Avatar
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    Hi Dave, yes there is a globla variable GLubyte ***IndiaMapPPM and yes it return 0 when it is success.

    Is it something to do with the GLubyte datatype. I suppose there is no difference between a char and GLubyte. And the following is a snap fo code where it show the way i am readin value from ppm file.

    Code:
     for( RowIndex = 0; RowIndex < Row; RowIndex++ )
              for( ColumnIndex = 0; ColumnIndex < Column; ColumnIndex++ )
                   fscanf( ppmFile, "&#37;d%d%d", &IndiaMapPPM[RowIndex][ColumnIndex][0],
                                              &IndiaMapPPM[RowIndex][ColumnIndex][1],
                                              &IndiaMapPPM[RowIndex][ColumnIndex][2] );
    Assuming that i have read the width and height of the ppm file. And

    Code:
    glDrawPixels( Width, Height, GL_RGB, GL_UNSIGNED_BYTE, IndiaMapPPM );
    ssharish
    Last edited by ssharish2005; 02-25-2008 at 09:46 PM.

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    There doesn't appear (to me, late at night) anything wrong here; although we're just allocating memory here ... there's many more chances to get it wrong elsewhere.

    As noted, make sure you're not hiding this global variable with a local one elsewhere, that you fill it in at some point, etc.

    I hope you're consistently using IndiaMapPPM[h][w][r] as a GLubyte. You shouldn't try to guess unless you have a good reason.

  5. #5
    CSharpener vart's Avatar
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    fscanf( ppmFile, "&#37;d%d%d",

    hmmm - what is the format of the file?
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  6. #6
    Registered User ssharish2005's Avatar
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    Hi Vart, here is a snap of my ppm file.

    Code:
    P3
    # LEAD Tech.
    628 658
    255
    255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 
    255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 
    255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 
    255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 
    255 255 255 255 255 255 255 255 255 255 255 255 255 255....
    Blue - States, what type of file
    DarkOrange - Information which is been commented out
    Magenta - Row Column
    Lime - max color

    The interesting part here is, when I delcare the array straight away like

    Code:
    GLubyte IndiaMapPPM[628][658][3];
    It just works fine. But when I allocate memory dynamically it gives me problem. If there was some problem with memory allocation or not allocated enough memory, i should have got sef fault when reading value into array. I font even get that. When I draw the pixel values, it just drawa call black, which i pretty wired. But this donst happen when I array is statically declared.

    Here is some more bit of code of my PPMread function.

    Code:
    void ReadPPMFile( void )
    {
         FILE *ppmFile;
         unsigned char Buffer[BUFSIZ];
         unsigned int Row, Column, MaxColor;
         int RowIndex, ColumnIndex, Flag = 0;
         
         if( ( ppmFile = fopen( PPMFILENAME, "r") ) == NULL )
         {
             printf("Error: PPM file cannot be opened\n");
             getchar();
             exit( 1 );
         }
         
         if( fgets( Buffer, sizeof(Buffer), ppmFile ) != NULL )
         {
             if( strncmp( Buffer, "P3", 3 ) == 0)
             {
                 printf("Error: File is not an ppm format\n");
                 getchar();
                 exit( 1 );
             }
         }
         else
         {
             printf("Error: File is empty\n");
             getchar();
             exit ( 1 );
         }
         
         while( fgets( Buffer, sizeof( Buffer ), ppmFile) != NULL )
         {
             if( Buffer[0] == '#' )
                 continue;
             
             if( sscanf( Buffer, "&#37;d %d %d", &Row, &Column, &MaxColor ) != 3 )
             {
                 if( sscanf( Buffer, "%d %d", &Row, &Column ) != 2 )
                 {
                     printf("Error: Reading row and column failed\n");
                     getchar();
                     exit( 1 );
                 }
                 else
                 {
                     if( fgets( Buffer, sizeof( Buffer ), ppmFile) != NULL )
                     {
                         if( sscanf( Buffer, "%d", &MaxColor) != 1)
                         {
                             printf("Error: reading max color failed\n");
                             getchar();
                             exit( 1 );
                         }
                         break;
                     }
                 }
             }
             else
                 break;
         }
         
         Width = Row;
         Height = Column;
         
         /* I have just commented this part since it wasn't working. */
         /* if( AllocateMemory() )
             exit(1);          */
    
         for( RowIndex = 0; RowIndex < Row; RowIndex++ )
              for( ColumnIndex = 0; ColumnIndex < Column; ColumnIndex++ )
                   fscanf( ppmFile, "%d%d%d", &IndiaMapPPM[RowIndex][ColumnIndex][0],
                                              &IndiaMapPPM[RowIndex][ColumnIndex][1],
                                              &IndiaMapPPM[RowIndex][ColumnIndex][2] );
         
         fclose( ppmFile );
    }
    Thank you

    ssharish

  7. #7
    CSharpener vart's Avatar
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    it seems - you are messing to much with globals
    you allocation function insted of to receive dimentions as parameters uses some Width and Height values

    wile your function reading from file initializes Row and Column values.

    Stop messing with globals where you can just pass parameters to function
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  8. #8
    Registered User ssharish2005's Avatar
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    May be, I will try with sending parameter and see if that one works .

    Thank you

    ssharish

  9. #9
    Frequently Quite Prolix dwks's Avatar
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    Note -- you don't always get segmentation faults when you read or write memory you shouldn't be meddling with. It could be your memory; or it could be within the page (is that the right term?) that your program's memory lives in -- most operating systems cannot check the bounds of your accessing exactly. I think I saw 4MB as a value for Windows. In other words, depending on where your memory started, you might have to overwrite as much as 4MB beyond the end of an array before Windows will notice.

    For perfect bounds checking, I recommend Valgrind -- it's really good. Unfortunately, it only runs on Linux, so if you're using Windows, you'll have to find something else. There are lots of these sorts of tools around, however. http://en.wikipedia.org/wiki/Memory_debugger

    I think it's possible that you have some sort of buffer overrun elsewhere . . . .

    Code:
             if( Buffer[0] == '#' )
                 continue;
    Suggestion:
    Code:
    for(p = Buffer; isspace(*p); p ++);
    if(*p == '#') continue;
    dwk

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