Malloc, Realloc and Calloc Help/Suggestion

This is a discussion on Malloc, Realloc and Calloc Help/Suggestion within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> #include <stdbool.h> #include "project1.h" int main() { int i, r, NUM_ITEMS, t, ret, ava; int* numbers; NUM_ITEMS ...

  1. #1
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    Malloc, Realloc and Calloc Help/Suggestion

    Code:
    #include <stdio.h>
    #include <stdbool.h>
    #include "project1.h"
    
    
    int main()
    {
    int i, r, NUM_ITEMS, t, ret, ava;
    int*  numbers;
    NUM_ITEMS = 0;
    ava = 100;
    
    
    
    numbers =  malloc(100 * sizeof(int));
    while(((ret = scanf("&#37;d",&t)) != EOF) && (ret != 0))
    {   
        if (NUM_ITEMS <= ava)
        {
    	numbers[NUM_ITEMS] = t;
    	NUM_ITEMS++;
    } else
    {
     numbers = realloc(numbers, sizeof(numbers) + sizeof(int)*100);
     ava = ava + 100 ;  
     printf("%d\n",t);
    	numbers[NUM_ITEMS] = t;
    	printf("\t Array at %d = %d\n",NUM_ITEMS, numbers[NUM_ITEMS]);
    	NUM_ITEMS++;
    }    	
     
     
    }
     
    r = bubbleSort(numbers, NUM_ITEMS);
    	 
    r =  insertionSort(numbers, NUM_ITEMS);
     
    }
    I am doing a proj for class. the point is to make some sort function and let them have at. The problem is I am having issues with malloc. I though I understood the memory alloction stuff pretty well but when ever I try to run this on a file with alot of numbers (say 100000) I run into memory issues and the computer I am compiling on gets all upset. I have the sorts running and sorting the same number of element when I use a a size I define in the code.

    So, my question is, is my problem a result of the way I am mallocing here or should I look at me calloc call in my sorts or is it the computer?

    Here is an example of a sort

    Code:
    /*********************************************************
    int bubbleSort(int * a, int n);
    
    *********************************************************/
    int bubbleSort(int * number, int array_size)
    {
    int i, j, r, temp;
    int * array_sort;	
    
    	//Allocating array of same size as passed array.
    	array_sort = (int *)calloc(array_size,sizeof (int));
    
    	if(array_sort != NULL)
    	{
    	//printf("Array created of size \n",array_size);
            }
            else
            {
                    //printf("Not enough memory\n");
                    exit(1);
            }
    // Bubble Code
    	
    // Clean-up
     free (array_sort);   
    	return(0);
    }
    Thanks for any suggestion
    Last edited by zensatori; 04-13-2007 at 07:50 PM.

  2. #2
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    Code:
    -bash-3.1$ ./proj1 < 100000.txt
    463480570
             Array at 101 = 463480570
    *** glibc detected *** ./proj1: realloc(): invalid next size: 0x0969a008 ***
    ======= Backtrace: =========
    /lib/libc.so.6[0x94181b]
    /lib/libc.so.6(__libc_realloc+0xec)[0x943605]
    ./proj1[0x8048558]
    /lib/libc.so.6(__libc_start_main+0xdc)[0x8f1724]
    ./proj1[0x8048471]
    ======= Memory map: ========
    This is what I see.
    But is a send it 10000 elements it works fine.

  3. #3
    ATH0 quzah's Avatar
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    Does this work?
    Code:
    #include<stdlib.h>
    int main( void )
    {
        int *numbers = malloc( 100000 * sizeof *numbers );
        if( number )
            free( numbers );
        return 0;
    }
    Or does it crash? I really doubt your issue is with malloc. You're probably blowing your stack space all to hell.


    Quzah.
    Hope is the first step on the road to disappointment.

  4. #4
    Just Lurking Dave_Sinkula's Avatar
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    Here are a couple of Things Not To Do:
    Code:
    while(((ret = scanf("&#37;d",&t)) != EOF) && (ret != 0))
    {   
        if (NUM_ITEMS <= ava)
    It would be better to check the scanf attempt against success; i.e., check whether the return value is 1. But that's just my footnote; you do check, but in an unnecessary manner.

    And arrays of size N may be indexed from 0 to N-1. The <= goes one beyond the end of the array.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  5. #5
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    Quote Originally Posted by Dave_Sinkula View Post
    Here are a couple of Things Not To Do:
    Code:
    while(((ret = scanf("%d",&t)) != EOF) && (ret != 0))
    {   
        if (NUM_ITEMS <= ava)
    It would be better to check the scanf attempt against success; i.e., check whether the return value is 1. But that's just my footnote; you do check, but in an unnecessary manner.

    And arrays of size N may be indexed from 0 to N-1. The <= goes one beyond the end of the array.
    Thanks for the suggestion. I kind of forgot that scanf returns anything :/

    So, my malloc ing looks ok?

  6. #6
    ATH0 quzah's Avatar
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    Quote Originally Posted by zensatori View Post
    So, my malloc ing looks ok?
    That depends. What doe sizeof( int ) give you? It's possible that 100,000 won't fit in your int.


    Quzah.
    Hope is the first step on the road to disappointment.

  7. #7
    and the hat of int overfl Salem's Avatar
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    > numbers = realloc(numbers, sizeof(numbers) + sizeof(int)*100);
    Well this doesn't expand your array by 100 ints, not by a long way.

    sizeof(numbers) just tells you the pointer size, not how much memory you're pointing at.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  8. #8
    Frequently Quite Prolix dwks's Avatar
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    Expanding on that: sizeof(numbers) is like saying sizeof(int *), which will probably be 2 or 4. You probably want to use ava * sizeof(int) or something.
    dwk

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