Thread: Sorting algorithm with dynamic memory allocation help

Hello I am fairly new to dynamic memory allocation and I keep getting a segmentation fault in this code of mine. Could anyone tell me where my error is or could be?

This is what the method should do:
void sortStringsByReversePoints(char **myWords): This function sorts the char* values (i.e. strings) of myWords in descending order of point value by calling getWordPoints as a helper function and comparing adjacent words. This simple (but inefficient) sorting algorithm starts at the beginning of myWords array and sweeps to the end comparing adjacent values and swapping if they are out of order. After N (length of the array) sweeps the array is fully sorted. Note that efficiency can be improved by a factor of 2 by shortening each successive sweep by one, since the first sweep will have guaranteed the minimum point value word is the last element of the array, the next sweep guarantees the last two elements are correct, and so on....Additionally, if a given sweep results in zero swaps then the array is sorted and you can return immediately.

Sizeof(words) returns the size of the pointer not the actual length of the array, I believe. You should pass in the length of your arrays into the function parameters.

Code:

#include<stdio.h>#include<stdlib.h>
#include<string.h>


#define BUFFER_SIZE 256
// returns an array of strings (char[])
// last entry is a NULL pointer
char **getListOfWords(char filename[])
{
    FILE *fp;
    char buffer[BUFFER_SIZE];
    char **words;
    int M, nLines = 0, nAlloc = 1;
    
    // initialize array of char pointers (for strings)
    words = (char **)malloc(nAlloc*sizeof(char *));
    
    fp = fopen(filename, "r");
    while(!feof(fp))
    {
        fscanf(fp, "%s", buffer);
        M = strlen(buffer);
        words[nLines] = (char *)malloc((M+1)*sizeof(char));
        strcpy(words[nLines], buffer);
        
        nLines++;
        if(nLines >= nAlloc)
        {
            nAlloc *= 2;
            words = (char **)realloc(words, nAlloc*sizeof(char *));
        }
    }
    words[nLines] = NULL;
    words = (char **)realloc(words, (nLines + 1)*sizeof(char *));
       
    fclose(fp);
    
    return words;
}


void freeWords(char **words)
{
    int i;
    
    for(i=0; words[i] != NULL; i++)
    {
        free(words[i]);
    }
    free(words);
}


int canWeMakeIt(char word[], char letters[])
{
	int n = strlen(letters) + 1;
	int i;
	char temp[n];
	strcpy(temp,letters);
	int found;
	for(i=0;i<strlen(word);i=i+1) //for each char in word, search temp
	{
			found = 0;
			for(n=0;n<strlen(temp);n=n+1)
			{
				if(word[i] == temp[n])
				{
					temp[n] = '-';
					found = 1;
					break;
				}
			}
			
			// if i not in temp
			if(found==0)
			{
				return 0;
			}
	}
	return 1;
	
}


// the code below does not work: Tue Nov 12, 2:16 PM
char **getScrabbleWords(char **allWords, char letters[])
{
	int nAlloc;
	int i;
	nAlloc = 1;
	char ** myWords = (char **) malloc(nAlloc*sizeof(char *));
	for(i=0;i<=(sizeof(allWords));i++)
	{
		if(canWeMakeIt(allWords[i],letters)==1) //it can be made
		{
			myWords[nAlloc-1] = allWords[i];
			nAlloc = nAlloc +1;
			myWords = (char **) realloc(myWords,(nAlloc*sizeof(char *)));
		}
	}
	myWords[nAlloc-1] = NULL;
	return myWords;
}


int getWordPoints(char word[])
{
    int letterPoints[] = {1, 3, 3, 2, 1, 4, 2, 4, 1, 8, 5, 1, 3, 1, 1, 3, 10,1, 1, 1, 1, 4, 4, 8, 4, 10};
    int position;
    int points;
    int i;
    for(i=0;i<=(sizeof(word));i=i+1)
    {
		////'z' - letter
		position = word[i] - 'a';
		points = points + letterPoints[position];
	}
	return points;
}


void sortStringsByReversePoints(char **myWords)
{
    int i, j, length;
    char *swap = (char *)malloc(1*sizeof(char *));
    for(i = 0; i <sizeof(myWords); i++)
    {
        for(j = 1; j < sizeof(myWords); j++)
        {
            if (strlen(myWords[i]>= strlen(myWords[j])))
                      length = strlen(myWords[i]);
            else
                      length = myWords[i];
            swap = (char *) realloc(myWords,(length*sizeof(char *)));
            if(getWordPoints(myWords[i])< getWordPoints(myWords[j]))
            {
                *swap = myWords[i];
                myWords[i] = myWords[j];
                myWords[j] = *swap;
            }
        }
    }
}


int main(int argc, char *argv[])
{
    char **allWords, **myWords;
    int i, j, M;
    
    allWords = getListOfWords("wordlist.txt");
    myWords = getScrabbleWords(allWords, argv[1]);
    /*sortStringsByReversePoints(myWords);
    
    
    for(i=0; myWords[i] != NULL; i++)
    {
        printf("%d %s\n", getWordPoints(myWords[i]), myWords[i]);
    }
    
    
    for(i=0; allWords[i] != NULL; i++)
    {
        printf("Word %d: %s\n", i, allWords[i]);
    }
    
    
    
    
     //Test cases for canWeMakeIt - un-comment when testing - remove before submitting
    printf("canWeMakeIt(\"abba\", \"ab\") = %d\n", canWeMakeIt("abba", "ab"));
    printf("canWeMakeIt(\"ab\", \"aba\") = %d\n", canWeMakeIt("ab", "aba"));
    */




    freeWords(allWords);
    free(myWords);
    
    return 0;
}

Would that work? Does strlen work in the same way as a one dimensional array when you use it in a two dimensional array?