Loop will not increment past 8? - c

Question

I have a loop that involves a dynamically allocated array in C. For some reason it crashes after flag increments 7 times. This wasn't happening before I was reallocating the size of the array. Here is the code:
for (int i = 0; i < length-1; i++)
{
if (audio_samples[i] > threshold && run)
{
*event_flags = (int*)realloc(*event_flags, sizeof(int)*(flag+1)); // reallocate the size of the array
*event_flags[flag] = i;
// printf("FLAG CREATED! %i\n ", i);
printf("EVENT FLAG %i %i\n",flag, *event_flags[flag] );
if (flag >5) {
printf("%d\n", i);
}
flag++;
run = false;
}
Any ideas? Please keep in mind that the size of the array is indeed the same value as length. Here is an example of my errors:
EDIT 1
FILE ONE:
int *event_positions = (int *) malloc(1 * sizeof(int)); // let us start with 1 and then add more within the method. This should continue until we have all the flags we want.
int number_of_flags = event_extractor(vocal_data, size, event_positions);
FILE TWO:
float g_THRESHOLD_FACTOR = 2.3; // THIS INCREASES THE THRESHOLD VALUE.
int event_extractor (int *audio_samples, unsigned int size_of_audio ,int *event_flags)
{
int length = (int)size_of_audio;
// * * * * * * * * * * * * * * * * * *
// RECTIFY VALUES (MAKE ABSOLUTE) (MAKE ALL POSITIVE)
int *rectified_audio = (int *) malloc(length * sizeof(int)); // I took this line from wave header reader. The number is the number of samples of the hip hop track.
make_values_absolute(audio_samples, length, rectified_audio);
// If I convert to signed ints here would the method run more efficiently?
// * * * * * * * * * * * * * * * * * * * *
// LOW PASS FILTER
int *lopass_samples = (int *) malloc(length * sizeof(int)); // I took this line from wave header reader. The number is the number of samples of the hip hop track.
lopass(rectified_audio, length,0.5, lopass_samples);
int number_of_flags = apply_threshold (lopass_samples, length, &event_flags);
printf("\n\n\n NUMBER OF EVENTS AAAA --- %d\n", number_of_flags);
for (int i = 0; i < number_of_flags; i++) {
printf("FLAG %i -- %d \n", i, event_flags[i]);
}
return number_of_flags;
}
int apply_threshold (int *audio_samples, unsigned int size_of_audio, int **event_flags)
{
int flag = 0; // this will be the number of flags that I have
bool run = true; // this will make sure that a minimum amount of time passes before I grab another flag. It's a guard.
int counter = 0; // this is the counter for the above guard.
printf("\n\nCURRENT MINIMUM TIME: 20100 SAMPLES \n\n");
// event_flags[0] = 1; // this first one is a dud. within the loop we will automatically start adding flags
int threshold = calculate_threshold_value(audio_samples, size_of_audio);
printf("\n\n this is the threshold %d \n\n", threshold);
int length = (int)size_of_audio;
printf("LENGTH OF VOCAL AUDIO %d \n", length );
for (int i = 0; i < length-1; i++)
{
if (audio_samples[i] > threshold && run)
{
// ** is this realloc working ?
// event_flags = (int*)realloc(event_flags, sizeof(int) * (flag+1));
*event_flags = (int*)realloc(*event_flags, sizeof(int)*(flag+1)); // reallocate the size of the array
*event_flags[flag] = i;
// printf("FLAG CREATED! %i\n ", i);
printf("EVENT FLAG %i %i\n",flag, *event_flags[flag] );
if (flag >5) {
printf("%d\n", i);
}
flag++;
run = false;
}
if (!run) {
counter++;
if (counter > 20100) { // hardcode minimum size for now.
counter = 0;
run=true;
}
}
}
printf("\n\n\n NUMBER OF EVENTS --- %d\n", flag);
for (int i = 0; i < flag; i++) {
printf("FLAG %i -- %d\n", i, *event_flags[i]);
}
printf("\nFIVE samples before and after my second flag: \n 0 should indicate a reach in the threshold\n");
for (int i = 0; i <10 ; i++) {
printf("VOCAL SAMPLE %i %i \n", i-5,audio_samples[*event_flags[1]+i-5] );
}
return flag;
}

Answer 1

First you shouldn't cast the return of realloc.
Then if I suppose that the type of that variable is int*
*event_flags[flag] = i;
There is one * too much no?
Edit: After your remark on leaving out the cast.
So if your event_flags is effectively int**, you are really on the wrong track. Seeing your use, I would guess you simply want an array of int instead. If you do that and then
event_flags[flag] = i;
without * everywhere, your problem should go away.
If you really need that indirection, you'd have to allocate not only the array event_flags but also all the individual arrays these pointers are pointing to, with something like
for (size_t j = startvalue; j < something; ++j)
event_flags[j] = malloc(whatever);

Answer 2

I think you may have a problem with the precedence of the * operator versus the [] operator. That is *event_flags[flag] and (*event_flags)[flag] do not reference the same memory location. The first one correspond to **(event_flags + flag) (probably not accessible), while the second one correspond to *((*event_flags) + flag) (what you want).
So, you should rewrite your code to:
int** event_flags;
// ...
*event_flags = realloc(*event_flags, sizeof(int) * (flag + 1));
(*event_flags)[flag] = i;