Double free/corruption? - c

Question

typedef struct {
int *info;
} row;
struct {
row* head;
int len;
int size;
} list;
int main{
list.len = 0;
list.size = 1;
list.head = malloc(list.size * sizeof(row));
//...... some other code that calls addRow (list.len) times
for (i = list.len - 1; i > 0; i--) {
free(list.head[i].info);/*****HERE**********/
}
free(list.head);
}
void addRow(int* data) {
int i;
if (list.len == list.size) {
row *temp = malloc(sizeof(row) * list.size * 2);
if (temp == NULL) {
fprintf(stderr, "Error (enter): (Line ##) Insufficient memory.\n");
return;
}
for (i = 0; i < list.len; i++) {
temp[i] = list.head[i];
}
free(list.head);
list.head = temp;
}
list.head[list.len].info = malloc(sizeof(int) * numCols);
for (i = 0; i < numCols; i++) {
list.head[list.len].info[i] = data[i];
}
list.len++;
}
This is the code that I used to addRow is were I malloc all the data. and I don't see why I'm getting a double free/ corruption error. At the area I marked HERE, I believe I am malloc-ing for all instances of info in the row struct, These line are the only ones doing malloc/free.
I just want to get into the habit free-ing properly when terminating the program.
FULL PROGRAM:
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
typedef struct {
int *info;
} row;
struct {
row* head;
int len;
int size;
} list;
static int sortCol, numCols;
int qSortCompare(const void*, const void*);
void printList();
int processInput();
void nullify(char*, int);
int main(int n, char **args) {
sortCol = 1;
numCols = 0;
if (n > 1 && args[1][0] == '-' && args[1][1] == 'c') {
sortCol = atoi(args[2]);
}
list.len = 0;
list.size = 1;
list.head = malloc(list.size * sizeof(row));
processInput();
if (sortCol < 1 || sortCol > numCols) {
fprintf(stderr, "Error (enter): (Line ##) Invalid column to sort.\n");
return 1;
}
printList();
qsort(list.head, list.len, sizeof(row), &qSortCompare);
printf("\n");
printList();
int i;
printf("add1:%p\nadd2:%p\n", list.head[0].info, list.head[1].info);
for (i = 0; i < list.len; i++) {
free(list.head[i].info);
}
free(list.head);
return 0;
}
void nullify(char* str, int n) {
int i;
for (i = 0; i < n; i++)
str[i] = '\0';
}
int parseInt(char *str, int index) {
int num = -1;
sscanf(str + index, "%d", &num);
return num;
}
void addRow(int* data) {
int i;
if (list.len == list.size) {
row *temp = malloc(sizeof(row) * list.size * 2);
if (temp == NULL) {
fprintf(stderr, "Error (enter): (Line ##) Insufficient memory.\n");
return;
}
for (i = 0; i < list.len; i++) {
temp[i] = list.head[i];
}
free(list.head);
list.head = temp;
}
list.head[list.len].info = malloc(sizeof(int) * numCols);
if (list.head[list.len].info == NULL) {
fprintf(stderr, "Error (enter): (Line ##) Insufficient memory.\n");
return;
}
for (i = 0; i < numCols; i++) {
list.head[list.len].info[i] = data[i];
}
list.len++;
}
int processInput() {
int i, maxChars = 200, totalN = 0;
int *nums, curNumIndex = 0, onNum, curNum;
numCols = maxChars / 2;
nums = (int*) (malloc(sizeof(int) * numCols));
char str[maxChars], ch;
for (i = 0; i < numCols; i++) {
nums[i] = -1;
}
while (!feof(stdin)) {
nullify(str, maxChars);
fgets(str, maxChars, stdin);
onNum = isdigit(str[0]);
curNumIndex = 0;
for (i = 0; i < maxChars; i++) {
ch = str[i];
if ((!isspace(ch)) && (!isdigit(ch)) && (ch != '\0')) {
fprintf(stderr, "Error 1: (Line ##) Invalid char in input.\n");
//return 0;
}
if (isspace(ch) && onNum) {
curNum = parseInt(str, curNumIndex);
curNumIndex = i;
nums[totalN % numCols] = curNum;
totalN++;
if (totalN % numCols == 0)
addRow(nums);
} else {
onNum = isdigit(str[i]);
}
if (ch == '\n' || ch == '\0')
break;
}
if (numCols > totalN) {
if (totalN > 0) {
numCols = totalN;
addRow(nums);
} else {
fprintf(stderr,
"Error (enter): (Line ##) Invalid first line of input.\n");
}
}
if (ch != '\n' && ch != '\0') {
fprintf(stderr,
"Error (enter): (Line ##) A row from input too long.\n");
//return 0;
}
}
return 1;
}
int qSortCompare(const void *c1, const void *c2) {
row *t1, *t2;
t1 = (row*)c1;
t2 = (row*)c2;
return t1->info[sortCol - 1] - t2->info[sortCol - 1];
}
void printList() {
int i, j;
for (i = 0; i < list.len; i++) {
for (j = 0; j < numCols; j++) {
printf("%10d ", list.head[i].info[j]);
}
printf("\n");
}
}
Program needs a EOF terminated input of integer numbers. Specifically with the same number of integers before the newline.
UPDATE: I used gdb to analysis the free part i it only fails on the second iteration, using for(i = 0; i < list.len; i++) and for(i = list.len - 1; i > 0 ; i--)

Answer 1

Another thing is that I don't see the update to list.size (it should be updated when resizing head)

Answer 2

"I just want to get into the habit free-ing properly when terminating the program."
The correct way to handle things like this is to free a non-NULL pointer and then set the pointer to NULL.
For example:
int* x = malloc (sizeof (int));
if (x != NULL) {
free (x);
x = NULL;
}
/* Misc. Code ... */
/* Now for whatever reason, you want to free x again */
/* This branch is never triggered, because you were smart enough to set x to NULL
* when you freed it the first time...
*/
if (x != NULL) {
free (x);
x = NULL;
}