Dynamically Allocating a 2D Array.

This is a discussion on Dynamically Allocating a 2D Array. within the C Programming forums, part of the General Programming Boards category; Originally Posted by Salem > if i did a realloc would it still trash all my previous strings? Your realloc ...

  1. #16
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    Quote Originally Posted by Salem
    > if i did a realloc would it still trash all my previous strings?
    Your realloc allocates one more char * pointer, not a string.
    All your existing strings (the pointers AND the memory they point to) are preserved. You don't need to do any more work with the strings you already have.

    so is
    Code:
     	another quick question
    
    Code:
    
    for(i = 0; i < num_of_inputs; i++)
             {
                Inputs[i] = malloc(cols * sizeof(char));
             }
    not needed?

  2. #17
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    Code:
    #define _GNU_SOURCE 1
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>
    #include <getopt.h>
    #include <sys/types.h>
    #include <sys/wait.h>
    
    typedef enum
    {
       FALSE = 0,
       TRUE = 1
    } Bool;
    
    int main()
    {
       ssize_t readReturn = 0;
       size_t bufLen = 0;
       char **Inputs = NULL;
       void *temp;
       char *input = NULL;
       int x = 0;
       Bool stillGoing = TRUE;
       int num_of_inputs = 0;
       int cols = 0;
       int old_cols = 0;
       int i = 0;
    
       while(stillGoing)
       {
         printf("enter text: ");
       
         readReturn = getline(&input, &bufLen, stdin);
       
         for(x = 0; x < strlen(input) + 1; ++x)
         {
            if(input[x] == '\n')
            {
               input[x] = '\0';
            }
         }
         
         if(strncmp(input, "exit", 4) == 0)
         {
             stillGoing = FALSE;
             break;
         }
            
         num_of_inputs++;
         cols = strlen(input) +1;
         
         printf("maybe here (inputs realloc)\n");
         temp = realloc(Inputs, num_of_inputs * sizeof(char *));
         
         if(temp)
         { 
            Inputs = temp;
            Inputs[num_of_inputs - 1] = input;
         }
         else
         {
            /*handle error*/
            printf("error\n");
            exit(EXIT_FAILURE);
         }
         
         
         
         
         /*if(cols > old_cols)
          {
             for(i = 0; i < num_of_inputs; i++)
             {
                Inputs[i] = malloc(cols * sizeof(char));
             }
             old_cols = cols;
          }*/     
    
          printf("maybe this is where it's seg faulted (strcpy)\n");
          /* strcpy(Inputs[num_of_inputs - 1], input);*/
    
           
          free(input);
          input = NULL;
          free(temp);
       }
       
       
       int z = 0;
       for(z=0; i < num_of_inputs-1; z++)
       {
          printf("%s\n", Inputs[z]);
       }
       
       free(Inputs);
       return 0;
    }
    new code but it still prints out junk then seg faults

  3. #18
    and the hat of wrongness Salem's Avatar
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    I'm just wondering if you actually try anything anyone else posts, or just find new and interesting ways to screw up your own code.

    Here, try this
    Code:
    #define _GNU_SOURCE 1
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <unistd.h>
    #include <getopt.h>
    #include <sys/types.h>
    #include <sys/wait.h>
    
    typedef enum
    {
      FALSE = 0,
      TRUE = 1
    } Bool;
    
    int main()
    {
      ssize_t readReturn = 0;
      size_t bufLen = 0;
      char **Inputs = NULL;
      void *temp = NULL;
      char *input = NULL;
      Bool stillGoing = TRUE;
      int num_of_inputs = 0;
      int i = 0;
    
      while(stillGoing)
      {
        printf("enter text: ");
        fflush(stdout);
    
        /* read a line, and blow away the newline */
        readReturn = getline(&input, &bufLen, stdin);
        if ( input[ strlen(input) - 1 ] == '\n' ) {
          input[ strlen(input) - 1 ] = '\0';
        }
    
        /* time to quit yet? */
        if(strncmp(input, "exit", 4) == 0)
        {
          stillGoing = FALSE;
          break;
        }
    
        /* save the pointer getline() allocated for us */
        num_of_inputs++;
        temp = realloc(Inputs, num_of_inputs * sizeof(char *));
        if(temp)
        {
          Inputs = temp;
          Inputs[num_of_inputs - 1] = input;
        }
        else
        {
          /*handle error*/
          printf("error\n");
          exit(EXIT_FAILURE);
        }
    
        /* make getline call malloc again for the next line */
        input = NULL;
      }
    
    
      /* print and free each line */
      for(i=0; i < num_of_inputs-1; i++)
      {
        printf("%s\n", Inputs[i]);
        free(Inputs[i]);
      }
    
      /* free all the pointers */
      free(Inputs);
      return 0;
    }
    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.
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