double free or corruption when using char** - c

Question

I'm allocating memory for my int *occurrences int *wordCounts and char **uniqueWords pointers and then at the end of the function that allocates the memory, i free them. However, when i compile the program i get an double free or corruption (!prev) aborting error. Is it caused by malloc,free or could it be due to how i initialize them inside the for loop ?
PS: I'm talking about the sortedCount() method, located towards the end
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#define MAX_STRING_SIZE 512 /* each line in the file can have up to 512 chars */
void populateWordsArray(int);
void reverse(int);
void first(int);
void middle(int);
void last(int);
int count(int, char*, int);
void sortedCount(int);
void determineUniqueWords(int *,char **, int);
void *malloc_or_end(size_t);
void* malloc_or_end(size_t sz) {
void *pointer;
pointer = malloc(sz);
if(pointer == NULL) {
printf("Out of memory, terminating.\n");
exit(-1);
}
return pointer;
}
/* turn into local */
FILE *file;
char **wordList;
void determineUniqueWords(int *occurrences, char **word, int N) {
int i = 0;
int j = 0;
for(i = 0; i < N; i++) {
if(occurrences[i] < 1) {
continue;
}
for(j = i + 1; j < N; j++) {
if(occurrences[j] == 1 && (strcmp(word[i],word[j])) == 0) {
occurrences[i]++;
occurrences[j] = 0;
}
}
}
}
/**
* Function populateWordsArray: reads N words from
* the given file and populates the wordList array with them.
* Has one argument: int N - the number of words to read.
* */
void populateWordsArray(int N) {
int i = 0;
while(i < N && (fscanf(file,"%s",wordList[i]) == 1)) { /* fscanf returns the number of successfully read items. If it's not 1, the read failed. Same as checking if fscanf reads the eof char. */
i++;
}
}
/**
* Function reverse: prints the words of the
* text file in reverse order.
* */
void reverse(int N) {
int i = 0;
for(i = N-1; i >= 0; i--) {
if(i == 0) {
printf("%s \n",wordList[i]);
} else if(strcmp(wordList[i],"") == 0) { /* improve this in main-> memory allocation */
continue;
}else {
printf("%s ",wordList[i]);
}
}
return;
}
/**
* Function first: Prints the first char of each
* word in the file.
* */
void first(int N) {
char firstChar;
int i = 0;
for(i = 0; i < N; i++) {
firstChar = *wordList[i];
printf("%c",firstChar);
}
printf("\n");
return;
}
/**
* Function middle: Prints the middle char of each word
* from the given file.
* */
void middle(int N) {
int middleIndex = 0;
int i = 0;
char midChar;
for(i = 0; i < N; i++) {
if((strlen(wordList[i]) % 2) == 0) { /* artios */
middleIndex = ((strlen(wordList[i]) / 2) - 1);
midChar = wordList[i][middleIndex];
}
else { /* peritos */
middleIndex = (int) ceil((strlen(wordList[i]) / 2));
midChar = wordList[i][middleIndex];
}
printf("%c",midChar);
}
printf("\n");
return;
}
/**
* Function last: Prints the last char of each
* word from the given file.
* */
void last(int N) {
int i = 0;
char lastChar;
int lastPos;
for(i = 0; i < N; i++) {
lastPos = strlen(wordList[i]) - 1;
lastChar = wordList[i][lastPos];
printf("%c",lastChar);
}
printf("\n");
return;
}
/**
* Function count: Prints the number of times
* that the selected word is found inside the N first words
* of the file.
* */
int count(int N, char *word, int callID) {
int i = 0;
int count = 0;
for(i = 0; i < N; i++) {
if(strcmp(word,wordList[i]) == 0) {
count++;
}
}
if(callID == 0) { /* if callID == 0 (main called count and we want the output) */
printf("%d",count);
printf("\n");
}
return count;
}
void sortedCount(int N) {
int i,j = 0;
int *occurrences;
int *wordCounts;
char **uniqueWords;
/* mem allocation */
uniqueWords = malloc_or_end(N * sizeof(char*)); /* worst case: every word is unique */
wordCounts = malloc_or_end(N * sizeof(int));
occurrences = malloc_or_end(N * sizeof(int));
/* initialize rootWord and occurrences for the "each word is unique and occurs only once" scenario */
for(i = 0; i < N; i++) {
uniqueWords[i] = malloc_or_end(MAX_STRING_SIZE * sizeof(char));
occurrences[i] = 1;
}
determineUniqueWords(occurrences,wordList,N);
/* populate the wordCounts & uniqueWords "arrays" with the appropriate data in order to sort them successfully */
for(i = 0; i < N; i++) {
if(occurrences[i] > 0) {
wordCounts[i] = count(N,wordList[i],1);
uniqueWords[i] = wordList[i];
}
}
for(i = 0; i < N; i++) {
free(uniqueWords[i]);
}
free(uniqueWords);
free(occurrences);
free(wordCounts);
return;
}
int main(int argc,char *argv[]) { /* argv[1] = op argv[2] = name argv[3] = <word> */
int N = -1;
int i = 0;
int spaceNum,nlNum = -1;
file = fopen(argv[2],"r");
if(file == (FILE *) NULL) { /* check if the file opened successfully */
fprintf(stderr,"Cannot open file\n");
}
fscanf(file,"%d",&N); /* get the N number */
wordList = malloc_or_end(N * sizeof(char *)); /* allocate memory for pointers */
for(i = 0; i < N; i++) {
wordList[i] = malloc_or_end(MAX_STRING_SIZE * sizeof(char)); /* allocate memory for strings */
}
populateWordsArray(N);
if(strcmp(argv[1],"-reverse") == 0) {
reverse(N);
} else if(strcmp(argv[1],"-first") == 0) {
first(N);
} else if(strcmp(argv[1],"-middle") == 0) {
middle(N);
} else if(strcmp(argv[1],"-last") == 0) {
last(N);
} else if((strcmp(argv[1],"-count") == 0) && argv[3] != NULL) {
i = count(N,argv[3],0);
} else if((strcmp(argv[1],"-sorted") == 0) && (strcmp(argv[3],"-count") == 0)) {
sortedCount(N);
} else {
/* i only wish i could print something here */
}
/* End of program operations */
for(i = 0; i < N; i++) {
free(wordList[i]);
}
free(wordList);
fclose(file);
return 0;
}

Answer 1

You are overwriting the value of a pointer to heap memory on line 185:
uniqueWords[i] = wordList[i];
This means that when you free it later, you are actually freeing the allocated rows in wordList. Now you have two problems:
When you free the wordList rows on lines 244-246, it will be a double-free
You are losing your reference to the uniqueWords rows.
Use strcpy to assign to a dynamically-allocated string rather than the = operation.