qsort Confusion

[picklesandmayo]

So after putting together this program, I am trying to sort multiple words alphabetically using [TEX]qsort ()[/TEX]. I have been using examples of [TEX]qsort ()[/TEX] found on the web and trying to adapt them to my cause, but all I've done so far is confuse myself. There are no errors, but it crashes when I run it.

Can anyone help?

#include <iostream>
#include <iomanip>
#include <search.h>
#include <string.h>
#include <cctype>
#include <stdio.h>
#include <stdlib.h>
using namespace std;


const int MAX = 100;

int compare(const void* pnum1, const void *pnum2);



void main()
{

	int i=0;
	int length;
	char *delim = " ";
	char *token;
	char string[MAX];
	char* array[255] = {0}; // assume max of 255 pointers
	cout << "Please enter a sequence of words. Press enter when completed" << endl;
	cin.getline(string, MAX);
	length = strlen (string);
	while (i < length)
	{
		string[i] = tolower(string[i]);
		i++;
	}
	cout << "Lower case the words are:\n"
		 << string << endl;


	token = strtok(string, delim);
	int c = 0;
	while (token != NULL)
	{
		
		cout << "token " << c << " is " << endl << token << endl;
		array[c] = token;
		token = strtok(NULL,delim);
		c++;
	}
	qsort(array[c], length, sizeof(int), compare);
	cout << "\n\nThe alphabetized words are:\n";
	for (i = 0; i < length; i++)
	{
		cout << array [i] << endl;
	}
}



	int compare(const void* pnum1, const void *pnum2)
	// compares two numbers, returns -1 if first is smaller
	// returns 0 is they are equal, returns 1 if first is larger
	{
	int num1, num2;

	num1 = *(int *)pnum1; // cast from pointer to void
	num2 = *(int *)pnum2; 

	if(num1 < num2)
	return -1;
	else
	if (num1 == num2)
	return 0;
	else
	return 1;
	}

Thanks, I'm fried :(

[Ancient Dragon]

>>qsort(array[c], length, sizeof(int), compare);
that is incorrect. You are sorting an array of char pointers not an array of integers qsort(array, c, sizeof(char*), compare);

Your compare function is also wrong. Why are you converting the char pointers to integers? I thought the strings are words? All you need is this?

int compare(const void* pnum1, const void *pnum2)
{
    return strcmp((char*)pnum1, (char*)pnum2);
}

for (i = 0; i < length; i++) { cout << array [i] << endl; }

wrong there too.length is the number of characters in the original string. What you want here is variable c, which is the number of valid pointers in array

[picklesandmayo]

Thank you. I am still having a problem though... I think I'm retarded :$

For some reason, the values in the array don't rearrange. Here's what I've got:

#include <iostream>
#include <iomanip>
#include <search.h>
#include <string.h>
#include <cctype>
#include <stdio.h>
#include <stdlib.h>
using namespace std;


const int MAX = 100;

int compare(const void *a, const void *b);



void main()
{

	int i=0;
	int length;
	char *delim = " ";
	char *token;
	char string[MAX];
	char* array[255] = {0}; // assume max of 255 pointers
	cout << "Please enter a sequence of words. Press enter when completed" << endl;
	cin.getline(string, MAX);
	length = strlen (string);
	while (i < length)
	{
		string[i] = tolower(string[i]);
		i++;
	}
	cout << "Lower case the words are:\n"
		 << string << endl;


	token = strtok(string, delim);
	int c = 0;
	while (token != NULL)
	{
		
		cout << "token " << c << " is " << endl << token << endl;
		array[c] = token;
		token = strtok(NULL,delim);
		c++;
	}
	qsort(array, c, sizeof(char*), compare);
	cout << "\n\nThe alphabetized words are:\n";
	for (i = 0; i < c; i++)
	{
		cout << array [i] << endl;
	}
}


int compare(const void *a, const void *b)
{
    return strcmp((char*)a, (char*)b);
}

[picklesandmayo]

anyone?

[Ancient Dragon]

Yes, see this thread . Just change your compare function as shown in that thread.

[picklesandmayo]

Thanks! It works now!