String is getting mysteriously knackered

This is a discussion on String is getting mysteriously knackered within the C Programming forums, part of the General Programming Boards category; Hi, I am trying to write a program to open zzt files, but I have come across a problem which ...

  1. #1
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    Unhappy String is getting mysteriously knackered

    Hi, I am trying to write a program to open zzt files, but I have come across a problem which I don't understand.

    If I printf the world.title string before I have called load_board it works fine, but if I try and printf it after load_board has been called it crashes. This makes me think that the load_board function is crapping over the world.title string, but I can't see where its touching it at all!

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <stdbool.h>
    
    /*    unsigned short int c;   / Two byte thingy */
    /*    unsigned char d;        / One byte thingy */
    
    
    /* Map structure */
    struct Sworld
    {
        int board_count;
        int start_board;
        
        int start_ammo;
        int start_gems;
        int start_health;
        int start_torches;
        
        int torch_cycles_left;
        int energiser_cycles_left;
        
        bool blue_key;
        bool green_key;
        bool cyan_key;
        bool red_key;
        bool purple_key;
        bool yellow_key;
        bool white_key;
        
        int start_score;
        
        char *title;
        int time_left;
        
        bool saved_game;
    }; 
    
    /* Tile structure */
    struct Stile
    {
        char code;
        char colour;
    };
        
    /* Board Structure */
    struct Sboard
    {
        char *title;
        char *message;
        struct Stile tile[1500];
        
        int object_count;
        int maximum_shots_fired;
        int time_limit;
        
        
        int board_north;
        int board_south;
        int board_west;
        int board_east;
        
        bool dark;
        bool teleport_when_hurt;    
    };    
    
    /* Functions */
    bool load_world(char *file_name);
    void load_board(FILE *file_pointer);
    
    /* Variables */
    struct Sworld world;
    struct Sboard board;
    
    int main(int argc, char *argv[])
    {
      
        if (load_world("BOB.ZZT") == false)
            printf("Cock up loading map\n");
           
       /* if (load_world("SAVED.SAV") == false)
            printf("Cock up loading map\n"); */
      
        printf("map title: %s\n", world.title);  
    
        if (world.saved_game == true)
            printf("Its a saved game\n");
        else
            printf("Its not a saved game\n");
    
        system("PAUSE");	
        
        free(world.title);
        return 0;
    }
    
    bool load_world(char *file_name)
    {
        FILE *file_pointer;
        char buffer[512];       /* Header goes here */
        int i, title_length;
        
        file_pointer = fopen(file_name, "r");
        if (file_pointer == NULL)
        {
            printf("FAILED opening world file: %s\n", file_name);
            system("PAUSE");
            return false;
        }
        else
            printf("Opened world file: %s\n", file_name);    
        
        for (i = 0; i < 512; i++)
            buffer[i] = getc(file_pointer);
        
        world.board_count = (unsigned short)buffer[2] + buffer[3] * 256;
        world.start_ammo = (unsigned short)buffer[4] + buffer[5] * 256;
        world.start_gems = (unsigned short)buffer[6] + buffer[7] * 256;
        world.blue_key = buffer[8];
        world.green_key = buffer[9];
        world.cyan_key = buffer[10];
        world.red_key = buffer[11];
        world.purple_key = buffer[12];
        world.yellow_key = buffer[13];
        world.white_key = buffer[14];
        world.start_health = (unsigned short)buffer[15] + buffer[16] * 256;
        world.start_board = (unsigned short)buffer[17] + buffer[18] * 256;
        world.start_torches = (unsigned short)buffer[19] + buffer[20] * 256;
        world.torch_cycles_left = (unsigned short)buffer[21] + buffer[22] * 256;
        world.energiser_cycles_left = (unsigned short)buffer[23] + buffer[24] * 256;
        world.start_score = (unsigned short)buffer[27] + buffer[28] * 256;
        
        title_length = buffer[29];
        world.title = malloc(title_length + 1);
        for (i = 0; i < title_length; i++)
            world.title[i] = buffer[30 + i];
        world.title[i] = '\0'; 
        
        world.saved_game = buffer[264];
        
        printf("Board Count: %d\n",world.board_count);
        
        printf("Loaded world: %s\n", world.title);
        
        load_board(file_pointer);
    
        fclose(file_pointer);
    
        return true;
    }    
    
    void load_board(FILE *file_pointer)
    {
        char *buffer;
        int i, board_size, title_length;
        int current_tile = 0;
        
        /* Read the board into the buffer */
        buffer = malloc(53);
        
        for (i = 0; i < 53; i++)
            buffer[i] = getc(file_pointer);
        
        /* Get the board size */    
        board_size = (unsigned short)buffer[0] + buffer[1] * 256; 
            
        /* Get the title */
        title_length = buffer[2];
        board.title = malloc(title_length + 1);
        for (i = 0; i < title_length; i++)
            board.title[i] = buffer[3 + i];
        board.title[i] = '\0';
        
        free(buffer);
        
        printf("Board title: %s\n", board.title);
        
        buffer = malloc(3);
        
        /* Get all the tiles put into the board.tile array */
        while (current_tile < 1500)
        {    
            for (i = 0; i < 3; i++)
                buffer[i] = getc(file_pointer);
            
            printf("Repeat amount: %d\n",buffer[0]);
            printf("Code: %d\n",buffer[1]);
            printf("Colour: %d\n",buffer[2]);
            
            
            
            for (i = 0; i < buffer[0]; i++)
            {
                board.tile[current_tile + i].code = buffer[1];
                board.tile[current_tile + i].colour = buffer[2];
                
                current_tile++;
            }   
            printf("Current_tile: %d\n",current_tile);
            system("PAUSE");
            
        }     
    
        free(board.title);
        free(buffer);
    }

  2. #2
    and the hat of wrongness Salem's Avatar
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    title_length = buffer[29];
    world.title = malloc(title_length + 1);

    title_length = buffer[2];
    board.title = malloc(title_length + 1);

    One of these is wrong for sure, since the second causes a memory leak if nothing else.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
    Registered User
    Join Date
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    Quote Originally Posted by Salem
    title_length = buffer[29];
    world.title = malloc(title_length + 1);

    title_length = buffer[2];
    board.title = malloc(title_length + 1);

    One of these is wrong for sure, since the second causes a memory leak if nothing else.
    I don't understand how its causing a memory leak. I am freeing board.title.

    edit: Just checked and the title_length is definately being set to the length of the string (not including terminating null).
    Last edited by kzar; 04-10-2005 at 08:06 AM.

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