strcpy and 2d malloc

This is a discussion on strcpy and 2d malloc within the C Programming forums, part of the General Programming Boards category; Hello everyone.. I have the following code: Code: for (k = 1; k < argc; k++) { cop = strcmp(argv[k], ...

  1. #1
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    strcpy and 2d malloc

    Hello everyone..
    I have the following code:

    Code:
    for (k = 1; k < argc; k++) {
            cop = strcmp(argv[k], "-n");
            if (!cop) {
                size = atoi(argv[k+1]);
            }
        }
    
    
        if ((player1 = malloc(size * sizeof(int *))) == NULL) {
            printf("\n\nCould not allocate memory!");
            return -1;
        }
        for (k = 0; k < size; k++) {
            if ((*(player1+k) = malloc(size * sizeof(int))) == NULL) {
                printf("\n\nCould not allocate memory!");
                return -1;
            }
        }
    and

    Code:
    for (k = 0; k < size; k++) {
            for (j = 0; j < size; j++) {
                strcpy(&player1[k][j], " ");
            }
         }
    when I run the code, instead of " " it shows NULL and segmentation fault.. Why?
    Last edited by Sotiris Kaniras; 01-25-2013 at 08:28 AM.

  2. #2
    SAMARAS std10093's Avatar
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    Soritis, please wrap your code with code tags

    Like this : [code]/*your program*/[/code]

    And also tell us why you are not happy with your code
    Code - functions and small libraries I use


    It’s 2014 and I still use printf() for debugging.


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  3. #3
    C++ Witch laserlight's Avatar
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    You access argv[k+1] before checking that k+1 < argc, so it is possible that you are calling atoi with a null pointer if k == argc - 1. Then, you fail to check that size is positive (or zero, but that would not be useful) before calling malloc using it.

    Next, what is player1? A mental disconnect between what it is (its type) and how you are using it could be the mistake that is causing the segmentation fault here.
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  4. #4
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    This is the desired result:

    Code:
    			   W H I T E
    		 A   B   C   D   E   F   G   H  
    
    
      		 -   -   -   -   -   -   -   -  
    		/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \
                 1 |   |   |   |   |   |   |   |   | 1
    		\_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \    
                   2 |   |   |   |   |   |   |   |   | 2
    		  \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \      
                     3 |   |   |   |   |   |   |   |   | 3
    		    \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \        
                       4 |   |   |   |   |   |   |   |   | 4
    		      \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \          
                         5 |   |   |   |   |   |   |   |   | 5
    		        \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \            
                           6 |   |   |   |   |   |   |   |   | 6
    		          \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \              
                             7 |   |   |   |   |   |   |   |   | 7
    		            \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \                
                               8 |   |   |   |   |   |   |   |   | 8
    		              \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ 
    			       A   B   C   D   E   F   G   H 


    And I get this:

    Code:
     
    Code:
             -   -   -   -   -   -   -   -  
       1 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 1
              \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \  
         2 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 2
              \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \    
           3 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 3
                \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \      
             4 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 4
                  \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \        
               5 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 5
                    \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \          
                 6 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 6
                      \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \            
                   7 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 7
                        \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \              
                     8 | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | (null)  | 8
                          \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \
                             A   B   C   D   E   F   G   H


    My program is divided to one file.h and 2 file.c..

    Header file:

    int design(char, char **player1, char **player2);

    designf.c

    Code:
    #include <stdio.h>
    #include <string.h>
    #include "hfiles.h"
    
    
    int design(char size, char **player1, char **player2)
    {
         int k, j, l, s, p, c, f, t, h;
         char *white[] = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"};
    
    
         h = 0;
         f = 0;
         c = 1;
         p = 0;
         t = 1;
         s = 0;
    
    
         for (k = 0; k < size; k++) {
            for (j = 0; j < size; j++) {
                strcpy(&player1[k][j], " ");
            }
         }
    
    
         for (k = 0; k < size; k++) {
             if (k == 0 && j == 0) {
                 if (size % 2 == 0) {
                     while (c < (size/2)) {
                           printf("    ");
                           c++;
                     }
                     printf("       W H I T E\n");
                 }
                 else {
                     while (c <= (size/2)) {
                          printf("    ");
                          c++;
                     }
                     printf("     W H I T E\n");
                 }
                 for (l = 0; l < size; l++) {
                     if (l == 0) {
                         printf("          ");
                     }
                     printf("%2s  ", white[l]);
                 }
                 printf("\n\n");
            }
    
    
            s = k;
            while (s > 0) {
                 printf("  ");
                   s--;
              }
              for (j = 0; j < size; j++) {
                  if (j <= size && k == 0) {
                      if (j == 0) {
                          printf("        ");
                      }
                      printf(" -  ");
                  }
                  if (j == size && k == 0) {
                      printf("\n");
                      for (l = 0; l < size; l++) {
                          if (l == 0) {
                              printf("          ");
                          }
                          if (l < size-1)
                              printf("/ \\_");
                          else
                              printf("/ \\");
                      }
                  }
              }
              printf("\n");
              while (f < k) {
                  printf("  ");
                  f++;
              }
              f = 0;
              if (k < 10) {
                  printf("   %d", k+1);
              }
              else
                 printf("  %d", k+1);
              while (p <= size) {
                   if (p < size) {
                       printf(" | %s ", player1[k][j]);
                   }
                   else
                      printf(" | %d", k+1);
                   p++;
              }
              p = 0;
              printf("\n");
              for (l = 1; l <= size; l++) {
                  if (l == 1) {
                      printf("          ");
                  }
                  if (k == 0) {
                      printf("\\_/ ");
                  }
                  else {
                      if (l == 1) {
                          while (t < k) {
                              printf("  ");
                              t++;
                          }
                          t = 1;
                      }
                      printf("\\_/ ");
                  }
              }
              if (k < size) {
                  printf("\\");
              }
          }
    
    
         printf("\n");
         if (size % 2 == 0) {
             while (h <= size/2) {
                 printf("    ");
                 h++;
             }
         }
         else {
             while (h <= size/2) {
                 printf("    ");
                 h++;
             }
             printf("   ");
         }
         printf("    ");
         for (k = 0; k < size; k++) {
             printf("%2s  ", white[k]);
         }
    
    
         return 0;
    }


    main.c

    Code:
    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    #include "hfiles.h"
    
    
    int main(int argc, char *argv[])
    {
        int k, j;
        char size, cop, **player1, **player2;
    
    
        cop = 1;
        size = 11;
        for (k = 1; k < argc; k++) {
            cop = strcmp(argv[k], "-n");
            if (!cop) {
                size = atoi(argv[k+1]);
            }
        }
    
    
        if ((player1 = malloc(size * sizeof(int *))) == NULL) {
            printf("\n\nCould not allocate memory!");
            return -1;
        }
        for (k = 0; k < size; k++) {
            if ((*(player1+k) = malloc(size * sizeof(int))) == NULL) {
                printf("\n\nCould not allocate memory!");
                return -1;
            }
        }
    
    
        if ((player2 = malloc(size * sizeof(int *))) == NULL) {
            printf("\n\nCould not allocate memory!");
            return -1;
        }
        for (k = 0; k < size; k++) {
             if ((*(player2+k) = malloc(size * sizeof(int))) == NULL) {
                 printf("\n\nCould not allocate memory!");
                 return -1;
             }
        }
    
    
        design(size, player1, player2);
        printf("\n\n");
    
    
        for (k = 0; k < size; k++) {
            free(*(player1+k));
            free(*(player2+k));
        }
        free(player1);
        free(player2);
    
    
        return 0;
    }
    Sorry for the size of the post!

  5. #5
    C++ Witch laserlight's Avatar
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    Right, since player1 is a char**, why do you use sizeof(int*)? Rather, you should use: player1 = malloc(size * sizeof(*player1))
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  6. #6
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    Quote Originally Posted by laserlight View Post
    Right, since player1 is a char**, why do you use sizeof(int*)? Rather, you should use: player1 = malloc(size * sizeof(*player1))
    I did it but nothing.. Still the same..

  7. #7
    C++ Witch laserlight's Avatar
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    Notice that there are other places that need a similiar fix.
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  8. #8
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    You could try the following as a debugging aid:
    1. Use calloc instead of malloc
    2. Use assert in appropriate places, for example

    Code:
    assert(&player1[k][j] != NULL);
    strcpy(&player1[k][j], " ")

  9. #9
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    Code:
    int design(char size, char **player1, char **player2)
    ...
    strcpy(&player1[k][j], " ");
    ...
    printf(" | %s ", player1[k][j]);
    I recommend brushing up your knowledge about string arrays in C (actually I recommend the whole tutorial).
    player1[k][j] is a character, not a string.

    Bye, Andreas

  10. #10
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    Quote Originally Posted by AndiPersti View Post
    Code:
    int design(char size, char **player1, char **player2)
    ...
    strcpy(&player1[k][j], " ");
    ...
    printf(" | %s ", player1[k][j]);
    I recommend brushing up your knowledge about string arrays in C (actually I recommend the whole tutorial).
    player1[k][j] is a character, not a string.

    Bye, Andreas
    I corrected it to "%c" but it doesn't write out anything.. why?

  11. #11
    SAMARAS std10093's Avatar
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    What Andreas said is correct. Probably you never reach the printf (this has to do with the counters) or you don't have something in the array to output.

    I agree on Andreas for the tutorial. Take a look at it, have a break and then continue
    Code - functions and small libraries I use


    It’s 2014 and I still use printf() for debugging.


    "Programs must be written for people to read, and only incidentally for machines to execute. " —Harold Abelson

  12. #12
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    Quote Originally Posted by std10093 View Post
    What Andreas said is correct. Probably you never reach the printf (this has to do with the counters) or you don't have something in the array to output.

    I agree on Andreas for the tutorial. Take a look at it, have a break and then continue
    No, it reaches the printf, I've tested it

  13. #13
    SAMARAS std10093's Avatar
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    print it like this
    Code:
    printf("|%c|\n", ...);
    to see exactly what the data is. It may be a whitespace.
    Code - functions and small libraries I use


    It’s 2014 and I still use printf() for debugging.


    "Programs must be written for people to read, and only incidentally for machines to execute. " —Harold Abelson

  14. #14
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    Code:
                         w h i t e
               a   b   c   d   e   f   g   h  
    
    
               -   -   -   -   -   -   -   -  
              / \_/ \_/ \_/ \_/ \_/ \_/ \_/ \
           1 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 1
              \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \  
             2 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 2
                \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \    
               3 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 3
                  \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \      
                 4 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 4
                    \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \        
                   5 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 5
                      \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \          
                     6 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 6
                        \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \            
                       7 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 7
                          \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \              
                         8 |  
     |  
     |  
     |  
     |  
     |  
     |  
     |  
    
    
     | 8
                            \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ 
                             a   b   c   d   e   f   g   h
    So, it works!

  15. #15
    SAMARAS std10093's Avatar
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    newline character I guess is that you have in there.
    Code - functions and small libraries I use


    It’s 2014 and I still use printf() for debugging.


    "Programs must be written for people to read, and only incidentally for machines to execute. " —Harold Abelson

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