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POMapping an integer to an array
 

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    <p>I recently started with C++; I'm an hobby programmer, and I know a bit of Python.</p> <p>I programmed a little snake. I wanted to insert another snake guided by the computer.</p> <p>I decided to put the possible direction that the snake can take in an enum:</p> <pre><code>enum directions{UP, DOWN, RIGHT, LEFT, IN, OUT, FW, RW,NONE}; void fill_map(std::map&lt;directions,V4&gt; &amp;map_vec); void fill_map(std::map&lt;int, directions*&gt; &amp;map_dir); void fill_map(std::map&lt;directions,directions&gt; &amp;map); </code></pre> <p>and map the enum for the needed function:</p> <pre><code>void fill_map(std::map&lt;directions,V4&gt; &amp;map_vec){ map_vec[UP] = V4(0,1,0,0); map_vec[DOWN] = V4(0,-1,0,0); //others } void fill_map(std::map&lt;directions, directions&gt; &amp;map){ map[UP]= DOWN; map[DOWN]= UP; //others } void fill_map_axis(std::map&lt;int, directions*&gt; &amp;map_dir){ directions array_x[2] = {RIGHT,LEFT}; map_dir[0] = array_x; directions array_y[2] = {UP,DOWN};//store the array map_dir[1] = array_y; directions array_z[2] = {FW,RW};//store the array map_dir[2] = array_z; directions array_w[2] = {IN,OUT};//store the array map_dir[3] = array_w; } </code></pre> <p>The fill_map functions are called in the snake constructor.<br> Basically what I wanted to do in the fill_map_axis is to map an integer corresponding to the index of the coordinate (0 coord x, 1 coord y etc) and map the two directions that move along those axis. So I stored an array of two directions. </p> <p>Now I call the function:</p> <pre><code>directions SnakeCPU::find_dir(V4 point){ //point is the target point directions dir; int index = get_coord_index(point); //get the index where to move double diff = head_pos[index]-point[index]; //find the difference between the head and the target point directions* axis = dir_coords[index]; //call the map containing the directions stored in an array. if(diff&lt;0.){ dir = *axis; //use the first } else if(diff&gt;0.) { axis++; dir = *axis; //use the second } else{ dir = NONE; } return dir; } </code></pre> <p>Although the map are initialized in the Snake constructor, it seems that the returned value from the pointer axis is a random memory block.</p> <p>So my question: do you see a mistake in the code? did I used the pointer axis with sense?</p> <p>I'm really not expert with pointer; in Python the map is instantiated with a dictionary like this:</p> <pre><code>dir_coords = {0:[LEFT,RIGHT], ...} </code></pre> <p>so I just need to call it:</p> <pre><code>axis = dir_coords[index] dir = axis[0] #or dir = axis[1] </code></pre> <p>edit:</p> <p>Snake constructor:</p> <pre><code>Snake::Snake() { fill_map(dir_vectors); fill_map(dir_coords); fill_map(opposite_dir); head_pos = V4(0.,0.,0.,0.); //other stuff... } </code></pre>
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    1. COYour `array_x` etc. are **local variables**, and you are only inserting a pointer to those arrays. After the function scope exits, those pointers are no longer valid. In short, everything is udders up. I recommend storing a `std::pair<direction, direction>` in your map.
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    2. COWhere is the code for the SnakeCPU constructor?
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    3. COWhat are `head_pos[] and point[]`? Also, `axis++; dir = *axis;` can be replaced with `dir = '*(++axis);`
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