How to remove item from array in C? - c

Question

I want to remove element from b->array as shown in below code:removeItem function
I have tried to remove 12.12 from the b->array = {11.11,12.12,13.13}but it leads to segmentation fault instead of printing {11.11,13.13}. can anybody help to get rid of it?
typedef struct
{
float val;
}data;
typedef struct
{
data **array;
int size;
}bag;
int main(int argc,char* argv[])
{
bag *str = createBag();
#ifdef DEBUG
printf("Inital values: %p %d\n",str->array,str->size);
#endif
data *iptr = createData(10.10);
data *iptr1 = createData(11.11);
data *iptr2 = createData(12.12);
data *iptr3 = createData(13.13);
data *iptr4 = createData(14.14);
#ifdef DEBUG
printf("%f\n",iptr->val);
#endif
addData(str,iptr);
addData(str,iptr1);
addData(str,iptr2);
addData(str,iptr3);
addData(str,iptr4);
printBag(str);
data *ptr = getData(str,4);
printf("Data item 4 is:%f\n",ptr->val);
int b = getBagSize(str);
printf("Size of bag: %d\n",b);
removeBack(str);
printBag(str);
removeFront(str);
printBag(str);
//cleanBag(str);
int s = searchBag(str,10.10);
printf("%d\n",s);
removeItem(str,12.12);
printBag(str);
return 0;
}
bag* createBag()
{
bag *str = (bag*)malloc(sizeof(bag));
str->array = NULL;
str->size = 0;
return str;
}
data* createData(float v)
{
data *iptr = (data*)malloc(sizeof(data));
iptr->val = v;
return iptr;
}
void addData(bag* b, data* d)
{
b->size++;
data** array1 = (data**)malloc(sizeof(data*)* b->size);
if(b->array!= NULL)
{
int i;
for(i = 0; i<b->size;i++)
{
array1[i] = b->array[i];
}
}
free(b->array);
array1[b->size-1] = d;
b->array = array1;
}
void printBag(bag *b)
{
int i;
for(i=0; i<b->size;i++)
{
printf("%f\n",b->array[i]->val);
}
}
data* getData(bag *b, int pos)
{
if(pos>5)
{
printf("change array position\n");
}
return b->array[pos];
}
int getBagSize(bag *b)
{
return b->size;
}
void removeBack(bag *b)
{
b->size--;
free(b->array[b->size]);
data **array2 = (data**)malloc(sizeof(data*)* b->size);
if(b->array!= NULL)
{
int i;
for(i = 0; i<b->size;i++)
{
array2[i] = b->array[i];
#ifdef DEBUG
printf("%f\n",array2[i]->val);
#endif
}
free(b->array);
b->array = array2;
}
}
void removeFront(bag *b)
{
b->size--;
free(b->array[0]);
data **array2 = (data**)malloc(sizeof(data*)* b->size);
if(b->array!= NULL)
{
int i;
for(i = 0; i<b->size;i++)
{
array2[i] = b->array[i+1];
#ifdef DEBUG
printf("%f\n",array2[i]->val);
#endif
}
free(b->array);
b->array = array2;
}
}
/*void cleanBag(bag *b)
{
int i;
for(i=0;i<b->size;i++)
{
free(b->array[i]);
}
free(b->array);
free(b);
}*/
int searchBag(bag *b,float v)
{
int i;
for(i=0;i<b->size;i++)
{
if(b->array[i]->val==v)
{
return (i+1);
}
}
return -1;
}
void removeItem(bag *b, float v)
{
int flag = 0,i = 0;
flag = searchBag(b,v);
if(flag != -1)
{
data **array2 = (data**)malloc(sizeof(data*)*(b->size-1));
for(i = 0; i < (b->size); i++)
{
if(i == (flag-1))
{
i = i + 1;
continue;
}
array2[i] = b->array[i];
}
free(b->array);
b->size--;
b->array = array2;
}
else
{
printf("Element is not found\n");
}
}

Answer 1

There are two mistakes in your code.
searchBag returns 0, if the float value is not found in the bag.
However, the function removeItem test for if(flag != -1). It should test for if(flag != 0) instead.
The reason for the seg. fault you encountered also lies in the removeItem function.
Note how the memory allocated for array2 is for b->size-1 elements only. Valid array indices for this array are in the range of 0 ... b->size-2.
Now, look at the for loop, and you will note that the index variable i will run from 0 to b->size-1. Exactly in the last iteration i will become b->size-1, so the code tries to write at the location array2[b->size-1] which is beyond the allocated memory of array2.
A possible fix of the removeItem function could look like this:
void removeItem(bag *b, float v)
{
int flag = 0;
int oldArrayIndex = 0;
int newArrayIndex = 0;
flag = searchBag(b,v);
if(flag != 0)
{
data **array2 = (data**) malloc(sizeof(data*)*(b->size-1));
for(oldArrayIndex = 0; oldArrayIndex < (b->size); oldArrayIndex++)
{
if(oldArrayIndex != (flag-1))
{
array2[newArrayIndex] = b->array[oldArrayIndex];
newArrayIndex++;
}
}
free(b->array);
b->size--;
b->array = array2;
}
else
{
printf("Element is not found\n");
}
}