Invalid initialization of dynamic array leads to read and write errors - c

Question

I'm trying to malloc an array of structs.
typedef struct {
long int val;
long int time;
long int last_used;
} pair;
so in my main I have
pair **fifoVM = (pair **) malloc(sizeof(pair *) * framecount);
pair **fifop1VM = (pair **) malloc(sizeof(pair *) * framecount + 1);
pair **fifop2VM = (pair **) malloc(sizeof(pair *) * framecount + 2);
pair **LRUVM = (pair **) malloc(sizeof(pair *) * framecount);
and I initialize all of the pairs using
void init(pair **frames, int size) {
for (int i = 0; i < size; i++) {
frames[i] = (pair *) malloc(sizeof(pair));
frames[i]->val = -1;
frames[i]->last_used = TIME_VAL;
frames[i]->time = TIME_VAL++;
}
}
But by the time I try to deallocate it, I get a corruption error from Valgrind.
I initially thought that the problem was using a pair* in the array but it still didn't work with just pair. I also thought it might be the pair going out of scope when init() returns but that also inst true because it would only deallocate the variable containing the pointer.
Also for some weird reason, LRUVM is the only array to crash, even though it's the last one.
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <time.h>
//since time.h only has millisecond resolution,
//I need to simulate time
int TIME_VAL = 0;
typedef struct {
long int val;
long int time;
long int last_used;
} pair;
//Allocate the pairs for a given array
void init(pair **frames, int size) {
//iterate through array
for (int i = 0; i < size; i++) {
//allocate memory and assign
frames[i] = (pair *) malloc(sizeof(pair));
frames[i]->val = -1;
frames[i]->last_used = TIME_VAL;
frames[i]->time = TIME_VAL++;
}
}
int main(int argc, char **argv) {
//Command line arguments
int framecount = atoi(argv[1]);
int x = atoi(argv[2]);
int NUM_ACCESSES = atoi(argv[3]);
int NUM_ITERATIONS = atoi(argv[4]);
for (int i = 0; i < NUM_ITERATIONS; i++) {
//Allocate Arrays
pair **fifoVM = (pair **) malloc(sizeof(pair *) * framecount);
pair **fifop1VM = (pair **) malloc(sizeof(pair *) * framecount + 1);
pair **fifop2VM = (pair **) malloc(sizeof(pair *) * framecount + 2);
pair **LRUVM = (pair **) malloc(sizeof(pair *) * framecount);
//initialize all of the pairs in the arrays
init(fifoVM, framecount);
init(fifop1VM, framecount + 1);
init(fifop2VM, framecount + 2);
init(LRUVM, framecount);
//deallocate arrays
freeList(fifoVM, framecount);
freeList(fifop1VM, framecount + 1);
freeList(fifop2VM, framecount + 2);
freeList(LRUVM, framecount);
}
}
void freeList(pair **vm, int framecount) {
for (int i = 0; i < framecount; i++) {
free(vm[i]);
}
free(vm);
}

Answer 1

Some of the allocation sizes are not computed correctly: malloc(sizeof(pair *) * framecount + 1) should be:
malloc(sizeof(pair *) * (framecount + 1))
Note that your data structure seem to have an indirection for no good reason. Why not allocate arrays of structures instead of arrays of pointers to structures allocated individually?
Here is a simpified version:
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>
#include <time.h>
//since time.h only has millisecond resolution,
//I need to simulate time
int TIME_VAL = 0;
typedef struct {
long int val;
long int time;
long int last_used;
} pair;
//Allocate the pairs for a given array
void init(pair *frames, int size) {
for (int i = 0; i < size; i++) {
frames[i].val = -1;
frames[i].last_used = TIME_VAL;
frames[i].time = TIME_VAL++;
}
}
int main(int argc, char **argv) {
//Command line arguments
if (argc < 5) return 1;
int framecount = atoi(argv[1]);
int x = atoi(argv[2]);
int num_accesses = atoi(argv[3]);
int num_iterations = atoi(argv[4]);
for (int i = 0; i < num_iterations; i++) {
//Allocate Arrays
pair *fifoVM = calloc(sizeof(pair), framecount);
pair *fifop1VM = calloc(sizeof(pair), framecount + 1);
pair *fifop2VM = calloc(sizeof(pair), framecount + 2);
pair *LRUVM = calloc(sizeof(pair), framecount);
if (fifoVM && fifop1VM && fifop2VM && LRUVM) {
//initialize all of the pairs in the arrays
init(fifoVM, framecount);
init(fifop1VM, framecount + 1);
init(fifop2VM, framecount + 2);
init(LRUVM, framecount);
//...
}
//deallocate arrays
free(fifoVM);
free(fifop1VM);
free(fifop2VM);
free(LRUVM);
}
}