C Tutorial - About Pointers

#define MAXROWS 5
#define MAXCOLUMNS 10
#define MAXLINELENGTH 80

typedef struct mapitem
{
  int row,column;
  char * line;
};

typedef struct mapitem * pmapitem;
typedef pmapitem row[MAXCOLUMNS];
typedef row * gridtype[MAXROWS];

int main(int argc, char* argv[])
{
  gridtype grid;
  pmapitem tempitem;
  int rowindex,colindex;

  for (rowindex=0;rowindex < MAXROWS; rowindex++) {
    
    grid[rowindex]=(row *)malloc(sizeof(row)) ;
    for (colindex=0;colindex < MAXCOLUMNS;colindex++)
    {
       
        tempitem = (pmapitem)malloc(sizeof(struct mapitem)) ;
        tempitem->row= rowindex;
        tempitem->column= colindex;

       
      tempitem->line = (char *)malloc(MAXLINELENGTH+1) ;
     /* clear the string */
    *tempitem->line ='\0';

    
    *(grid[rowindex])[colindex] = tempitem;
     }
   }

    
    (*grid[0][0])->line="Top Left Corner";
    (*grid[MAXROWS-1][0])->line="Bottom Left Corner";
    (*grid[0][MAXCOLUMNS-1])->line="Top Right Corner";
    (*grid[MAXROWS-1][MAXCOLUMNS-1])->line="Bottom Right Corner";
    return 0;
}

1. Each Row.
2. Each Item in each row.
3. Each Line (the char * field) in each item.

This completes this lesson. The next lesson will be on the advanced users of pointers.

• Learn About Pointers
• Allocating Memory
• Explanation of Example 1 Continued
• Explanation of Example 1 Continued
• Examples of Pointers
• Example 2- Using Pointers with a Struct
• About malloc and free
• Some Rules for Working with Pointers
• Some More Examples of Pointers in C
• Example of 2D Structure with Pointers