Valgrind error conditional jump - c

Question

I'm writing a program that loads input until a specific word is typed in,in this case its word "konec".Although my program seems to work just about ok,I can't solve this Valgrind error
==16573== Memcheck, a memory error detector
==16573== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==16573== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==16573== Command: ./s_main_o
==16573==
==16573== Conditional jump or move depends on uninitialised value(s)
==16573== at 0x4C2A020: strcmp (mc_replace_strmem.c:711)
==16573== by 0x4008D7: main (main.c:41)
==16573== Uninitialised value was created by a heap allocation
==16573== at 0x4C28CCE: realloc (vg_replace_malloc.c:632)
==16573== by 0x40089C: main (main.c:38)
==16573==
==16573== Conditional jump or move depends on uninitialised value(s)
==16573== at 0x4C2A024: strcmp (mc_replace_strmem.c:711)
==16573== by 0x4008D7: main (main.c:41)
==16573== Uninitialised value was created by a heap allocation
==16573== at 0x4C28CCE: realloc (vg_replace_malloc.c:632)
==16573== by 0x40089C: main (main.c:38)
==16573==
==16573==
==16573== HEAP SUMMARY:
==16573== in use at exit: 0 bytes in 0 blocks
==16573== total heap usage: 8 allocs, 8 frees, 1,125 bytes allocated
==16573==
==16573== All heap blocks were freed -- no leaks are possible
==16573==
==16573== For counts of detected and suppressed errors, rerun with: -v
==16573== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 4 from 4)
And here part of the used code
int main() {
int numberOfWords, i;
char** words;
char* word;
int* rarity;
char* konec = "konec";
int amount = 0;
double percentage;
words = malloc(10 * sizeof (char*));
rarity = calloc(256, sizeof (int));
numberOfWords = 0;
words[0] = 0;
int working = 1;
while (working == 1) {
int length = 0;
word = calloc((length + 1),sizeof (char));
char c;
while ((c = getchar()) != EOF) {
if (c == ' ' || c == '\n') {
break;
}
length++;
word = realloc(word, length + 1);
word[length - 1] = c;
}
if (strcmp(word, konec) == 0) {
working = 0;
free(word);
break;
}
}
}
I have found lots of topics discussing the same problem,but I wasn't able to find solution anyway.Thanks for your answers.

Answer 1

The problem is that you do not add a null terminator on reallocation:
word = realloc(word, length + 1);
word[length - 1] = c;
At this point, word string is not terminated, so strcmp may go off its end in search of null terminator. For example, when you type "ko", strcmp will determine that characters 0 and 1 are the same, and try checking word[2] - a location that your program did not set.
Add this line to fix the problem:
word[length] = '\0';
You should also add code to free word when comparison to konec is unsuccessful.
Note: You are not using realloc correctly: instead of assigning it back to word, you should assign it to temp, and check it for NULL. Otherwise, you would have no way of freeing previously allocated word when realloc fails.