Pointer and Structures..

This is a discussion on Pointer and Structures.. within the C Programming forums, part of the General Programming Boards category; I'm working on a maze solving program right now... But the problem is, I dont know how to access a ...

  1. #1
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    Pointer and Structures..

    I'm working on a maze solving program right now... But the problem is, I dont know how to access a pointer to pointer to struct data.

    Something like this

    struct path *solution_path in function A
    it points to struct tile *tile_list in another struct which points to:

    Code:
    struct tile {
        /*position of the tile on the maze*/
        int x;
        int y;
        
        /*current value of the tile*/
        int value;
    };
    I want to store values on 'value'... so how do I access value?
    I've been looking over the internet on how to do it... but I can't find any...

    doing something like solution_path->tile_list[].value doesn't seem to work...

  2. #2
    and the hat of wrongness Salem's Avatar
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    > doing something like solution_path->tile_list[].value doesn't seem to work...
    Something like seems?
    How is this accurate information?

    Did you try
    solution_path->tile_list->value
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  3. #3
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by CurlyBrace
    struct path *solution_path in function A
    it points to struct tile *tile_list in another struct which points to:
    You are probably just saying things wrong. If solution_path is a pointer to struct path, then it does not make sense for it to point to tile_list when tile_list is a pointer to struct tile.

    My guess is that you have something like this:
    Code:
    struct tile {
        /*position of the tile on the maze*/
        int x;
        int y;
         
        /*current value of the tile*/
        int value;
    };
    
    struct path {
        struct tile *tile_list;
    };
    Now, given:
    Code:
    struct path *solution_path;
    You want to access: solution_path->tile_list->value or solution_path->tile_list[i].value, where i is some valid index.
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    After trying that out, it does work but it crashes midway while assigning values to solution_path->tile_list[counter].value not sure what I'm doing wrong
    Code:
    struct path *solution_path;
    xy = width*height;
        
    solution_path = malloc(sizeof(int));
    solution_path->tile_list = malloc(sizeof(int)*xy);
    
    
    counter =0;    
    for(i=0;i<height;i++)    {
          for(j=0;j<width;j++)
          {
            solvemap[j][i] = (maze_data.grid+counter)->value; 
            counter++;
          }
        }  
    
    
        counter = 0;
        for(i=0;i<height;i++)
         {
             for(j=0;j<width;j++)
             {
               solution_path->tile_list[counter].value = solvemap[j][i];
               printf("%d", solution_path->tile_list[counter].value);
               counter++;
             }  
           printf("\n");
    
         }
    Last edited by CurlyBrace; 10-31-2012 at 10:45 PM.

  5. #5
    C++ Witch laserlight's Avatar
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    This is wrong:
    Code:
    solution_path = malloc(sizeof(int));
    solution_path is a pointer to struct path, therefore the space that should be allocated for what it points to should be sizeof(struct path), at least. We can do this by making use of the pointer itself:
    Code:
    solution_path = malloc(sizeof(*solution_path));
    Likewise, this is wrong:
    Code:
    solution_path->tile_list = malloc(sizeof(int)*xy);
    It should be:
    Code:
    solution_path->tile_list = malloc(sizeof(solution_path->tile_list[0]) * xy);
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