Problem with realloc

This is a discussion on Problem with realloc within the C Programming forums, part of the General Programming Boards category; Here is a snippet of code that displays the problem I am having with realloc in a much larger program: ...

  1. #1
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    Problem with realloc

    Here is a snippet of code that displays the problem I am having with realloc in a much larger program:

    Code:
    #include <stdlib.h>
    #include <stdio.h>
    
    int main()
    {
        
        int *int_array,counter, size,size1;
        
        printf("How many members in the array do you want: ");
        scanf("%d",&size);
    
    // Allocates memory for the int_array
    
        int_array=(int *)malloc(size*sizeof(int));
    
    // Places a value in each index position    
    
        for(counter=0;counter<size;counter++)
            int_array[counter]=10+counter;
    
        printf("\nThe array has the following elements: \n");
    
    // Prints values
    
        for(counter=0;counter<size;counter++)    
            printf("%d\n",int_array[counter]);
        
    
    
        printf("What would you like the new size to be: ");
        scanf("%d",&size1);
        
    // Should reallocate the array to size size1
    
        int_array=realloc(int_array,size);
    
        printf("\nThe array now has the following elements: \n");
    
    // Runs until counter is equal to the original size...When I increase the size using
    // realloc the values up until the original size should remain unchanged, but 
    // they are not when i print them out
    
        for(counter=0;counter<size;counter++)    
            printf("%d\n",int_array[counter]);
        system("PAUSE");
        return 0;
    }
    HERE IS THE OUTPUT I GET: (I ran this on two machines and it came up with the same numbers)

    Like I said, I am running into this problem in a much larger project, if anyone can help it would be greatly appreciated.

    How many members in the array do you want: 10

    The array has the following elements:
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    What would you like the new size to be: 11
    10
    11
    12
    13
    196697
    15
    3998784
    3998784
    18
    393302

  2. #2
    Beginner leiming's Avatar
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    int_array=realloc(int_array,size1);

    You forget to multiplus sizeof(int) to size.

    LeiMing.
    Last edited by leiming; 05-22-2008 at 10:07 PM. Reason: I don't find that it's size1 just now......

  3. #3
    Registered User
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    Apr 2008
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    You also are not actually using the new size1. You might also want to test the return value from realloc before you reassign your existing pointer.

    Code:
    new_array = realloc(int_array, size1 * sizeof(int));
    if(new_arr) int_array = new_array;
    else return -1; /* or whatever else */

  4. #4
    Registered User
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    11

    Thanks

    Wow...I fell like a dummy.

    Code:
    int_array=realloc(int_array,size1*sizeof(int));
    works perfectly.

    ...Also, thanks for the error checking hints...always a good idea

  5. #5
    C++まいる!Cをこわせ! Elysia's Avatar
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    22,411
    Also note that it is a bad idea to cast the return of malloc in a C program (explanation is in FAQ).
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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