Sorting algorithm for a Dynamic Array in C

Question

I am trying to sort a Dynamic Array that contains Costs as elements. This is my sorting function:

void ascending_sort(Controller* ctrl) //the function is in the controller
{
    int i,j;
    DynamicVector* CostList=getAll(ctrl->repo); //the getALL function returns the CostList that has Costs as elements
    for(i=0;i<getLen(CostList)-1;i++)
    {
        Cost* cost=(Cost*)getElementAtPosition(CostList,i); //getElementAtPosition returns the Cost at a certain position
        for(j=i+1;j<getLen(CostList);j++)
        {
            Cost* cost1=(Cost*)getElementAtPosition(CostList,j);
            if(cost->sum > cost1->sum)
            {
            Cost  aux=cost[i];
            cost[i]=cost[j];
            cost[j]=aux;
            }
        }
    }
}

The problem is when I want to print the costs. If I print them before sorting, everything goes right and prints the costs. If I sort the list and then print the sorted Costs I get a "Close Program" error, and the program crashes. This is the print function:

void PrintCosts(Console* console)
{
    DynamicVector* CostList=getAllCosts(console->ctrl);
    if (getLen(CostList))
    {
        int i;
        for(i=0;i<getLen(CostList);i++)
        {
            printf("\nCost %d\n\n",i+1);
            Cost *c=(Cost*)getElementAtPosition(CostList,i);
            PrintCost(c);
        }

    }
    else printf("No cost in the list!");
}

This is the struct:

typedef struct{
    int id;
    char* day;
    char* type;
    int sum;
}Cost;

This is the sorting function that is called in the console:

void AscendingSort(Console* console)
{
    ascending_sort(console->ctrl);
}

This is a function that returns a Cost* type:

Cost* initCost(char* day, char* type, int sum)
{
    Cost* c=(Cost*)malloc(sizeof(Cost));
    if(strlen(day)>0 && strlen(day)<=10)
    {
        c->day = copyString(day);
    }
    else
    {
        c->day=0;
    }
    if(strlen(type)>0 && strlen(type)<=20)
    {
        c->type = copyString(type);
    }
    else
    {
        c->type=0;
    }
    if(sum>0)
    {
        c->sum= sum;
    }
    return c;
}

Console:

Console* initConsole(Controller* ctrl)
{
    Console* console=(Console*)malloc(sizeof(Console));
    console->ctrl=ctrl;
    return console;
}

getElementAtPosition

TElem getElementAtPosition(DynamicVector* v, int pos)
{
    if(v->elem[pos])
        return v->elem[pos];
    else
        return 0;
}

typedef void* TElem;

Could you show the definitions for the Console-type and the definition of getElementAtPosition? — Morten Jensen
– Morten Jensen, Commented Mar 18, 2013 at 14:02
you're throwing void* all over the place. Your errors would probably be caught be the compiler if you defined explicit types for your system. You are asking the compiler to ignore type mismatches by casting to void* :) — Morten Jensen
– Morten Jensen, Commented Mar 18, 2013 at 14:20

Rohan · Accepted Answer · 2013-03-18 14:04:52Z

1

You are trying to access cost as array, in sort code

Cost  aux=cost[i];
cost[i]=cost[j];
cost[j]=aux;

which is not correct, assuming getElementAtPosition() return pointer to one item and not the array of items which are sequentially accessible i.e array.

You can only access one element through pointer notification like cost->sum and not cost[i].sum unless i==0.

answered Mar 18, 2013 at 14:04

Rohan

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1 Comment

user1849859 Over a year ago

And how should I write that portion of code? I wrote something like this: Cost* aux=cost1; cost=cost1; cost1=aux; but it doesn't work at all. :)

Morten Jensen · Accepted Answer · 2013-03-18 14:25:56Z

0

Sounds like you're getting a segfault. You haven't shown the functions that return the Cost* and you never validate the Cost* before dereferencing it. Maybe something's wrong in that area? I think I'd need some more source code to verify that.

Also I noticed this.

for(i=0;i<getLen(CostList);i++)
{
    printf("\nCost %d\n\n",i+1);
    Cost *c=(Cost*)getElementAtPosition(CostList,i); <-- typeof(C) == Cost*
    PrintCost(c);  <-- typeof(C) == Console*
}

You're using the variable c as both a Cost* and a Console*. This isn't a typesafe way of doing things, so I'm guessing you have some errors here. Can't tell without more code though :)

edited Mar 18, 2013 at 14:25

answered Mar 18, 2013 at 14:01

Morten Jensen

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