Dynamic array of strings - c

Question

I have to dynamically allocate array of words. Words are stored in a file separated by variable count of white-space characters. I don't know how many words is in the file a they can have variable length.
I have this code:
void readWord(FILE* stream, char *word, char first_c) {
word[0] = first_c;
char val;
int wlen = 1;
// isWhitespac is my function - tests if char is blank or '\n'
while ((val = fgetc(stream)) != EOF && isWhitespace(val) == 0) {
wlen++;
word = realloc(word, (wlen+1) * sizeof (char));
word[wlen-1] = val;
}
word[wlen] = '\0';
}
int readList(const char *file) {
FILE* f;
char **arr;
char val;
int wcount = 0;
arr = malloc(sizeof (char*));
f = fopen(file, "r");
while (fscanf(f, " %c", &val) == 1) {
wcount++;
arr = realloc(arr, wcount * sizeof (char *));
arr[wcount - 1] = malloc(sizeof (char));
readWord(f, arr[wcount-1], val);
printf("%s\n", arr[wcount-1]);
}
for (int i = 0; i < wcount; ++i) {
free(arr[i]);
}
free(arr);
fclose(f);
return 0;
}
It appears to work fine, it reads a prints all the words. But when I run the program with Valgrind the are too many errors, which I can't find. Could anyone help me? (I know I have to test if malloc and others went fine, it is just a test func.)
The Valgrind log is quite long, should I post it too?

Answer 1

One of the issues is that you do realloc inside readWord. If realloc allocates a new buffer and doesn't just extend the current one then your code will crash (you will double free the pointer) and this is what Valgrind picks up. To fix this I would rewrite the code so it returns a pointer instead of void.
char * readWord(FILE* stream, char *word, char first_c) {
word[0] = first_c;
char val;
int wlen = 1;
// isWhitespac is my function - tests if char is blank or '\n'
while ((val = fgetc(stream)) != EOF && isWhitespace(val) == 0) {
wlen++;
word = realloc(word, (wlen+1) * sizeof (char));
word[wlen-1] = val;
}
word[wlen] = '\0';
return word;
}
And then change the loop in readList to this:
while (fscanf(f, " %c", &val) == 1) {
wcount++;
arr = realloc(arr, wcount * sizeof (char *));
arr[wcount-1]=malloc(sizeof(char));
arr[wcount - 1] = readWord(f, arr[wcount-1], val);
printf("%s\n", arr[wcount-1]);
}