Problem with realloc()

This is a discussion on Problem with realloc() within the C Programming forums, part of the General Programming Boards category; Hello, I am using code::blocks on Windows plateform for my program. In my program, in one of the loop, I ...

  1. #1
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    Problem with realloc()

    Hello,

    I am using code::blocks on Windows plateform for my program. In my program, in one of the loop, I am using realloc function to increase the allocation space for one pointer to structure. It almost always fails and program does not run sucessful. For understanding, I tried the following program.

    Code:
    #include<stdio.h>
    #include<stdlib.h>
    int main(void)
    {
        int i, j, loop_end=15;
        double x=10.00, *y;
        //char x='A', *y;
        y=(double*)calloc(1, sizeof(double));
        //y=(char*)calloc(1, sizeof(char));
        *y=x;
        printf("\n\n  STARTING: @ %d, value= %lf\n\n",y, *y);
        //printf("\n\n  STARTING: @ %d, value= %c\n\n",y, *y);
        for(i=0; i<=loop_end-1; i++)
        {
            printf("\n Loop No: %d\n--------------",i);
            if((realloc(y, (i+2)*sizeof(double))) == NULL)
            //if((realloc(y, (i+2)*sizeof(char))) == NULL)
            {
                printf("\n\n In loop %d mem-err occured\n",i);
                free(y);
                getchar();
                return 0;
            }
            for(j=0; j<=i; j++)
                printf("\n [%2d] Address: %d   Value: %lf",
                       j, (y+j), *(y+j));
                //printf("\n [%2d] Address: %d   Value: %c",
                       //j, (y+j), *(y+j));
             *(y+i+1)=*(y+i)+1;
        }
        printf("\n Loop completed");
        free(y);
        getchar();
        return 0;
    }
    When I run it for char few loops run (sometimes 5, sometimes 6) and for double it never runs sucessfully even two loops (in compilation, no warning). Please let me know where I am doing some mistake in this ??

    Thanks and regards,
    Amal.

  2. #2
    DRK
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    realloc() doesn't always return the same pointer as input parameter.
    Code:
    new_pointer = realloc(old_pointer, new_size);

  3. #3
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    Thanks,
    Introducing second pointer solved the problem.......

  4. #4
    DRK
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    Quote Originally Posted by amalendu View Post
    Introducing second pointer solved the problem.......
    Actually, you could have used already existing pointer by assigning result of realloc() to it.
    Code:
    y = realloc(y, (i+2)*sizeof(double));

  5. #5
    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by DRK View Post
    Actually, you could have used already existing pointer by assigning result of realloc() to it.
    Code:
    y = realloc(y, (i+2)*sizeof(double));
    Except that generally means that if realloc fails you leak the original allocation.
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