Question

int heapSize = 20; //variable 
int left(int i) {
return (2 * i) + 1;
}

int right(int i) {
return (2 * i) + 2;
}

void heapify(string arr[], int i) {
int l = left(i);
int great=0;
int r = right(i);
if ( ((strcmp(arr[l].c_str(),arr[i].c_str()))>0) && (l < heapSize)) {
great = l;
}
else {
great = i;
}

if ( ((strcmp(arr[r].c_str(),arr[great].c_str()))>0) && (r < heapSize)) {
great = r;
}
if (great != i) {
string temp = arr[i];
arr[i] = arr[great];
arr[great] = temp;
heapify(arr, great); //Getting segment here 
}

}

void BuildMaxHeap(string arr[]) {
for (int i = (heapSize - 1) / 2; i >= 0; i--) {
heapify(arr, i);
}
}

void HeapSort(string arr[]) {
BuildMaxHeap(arr); //
for (int i = heapSize; i > 0; i--) {
string temp = arr[0];
arr[0] = arr[heapSize - 1];
arr[heapSize - 1] = temp;
heapSize = heapSize - 1;
heapify(arr, 0);
}

}

Getting segmentation fault with this string heap sort code for heapSize larger than 15, for example 20 elements.
Any idea about the reason?

I backtraced it in gdb and I get this

#0  0x0038124b in ?? () from /lib/tls/i686/cmov/libc.so.6
#1  0x08048f62 in heapify(std::string*, int) ()
#2  0x08049050 in heapify(std::string*, int) ()
#3  0x080490ae in BuildMaxHeap(std::string*) ()
#4  0x080490d3 in HeapSort(std::string*) ()
#5  0x080494f5 in main ()

So, what is wrong with the heapify function?

Answer 1

In the ifs you should check if the indexes are in the bounds of the array before you try to compare the stings:

if ( (l < heapSize) && (arr[l] > arr[great]) ) {