Thread: Error when freeing memory (allocated with realloc)

Hi everybody,

I am trying to make an adress book where I can store a persons name and his phone numbers.
I am using the Microsoft Visual C++ 2005 IDE.
There are 3 kinds of numbers :

Code:

enum number_type {MOBILE = 0, PRIVATE = 1, WORK = 2};

A contact record is represented by:

Code:

struct contact_record {
	char* contact_name;
	char*** numbers;
	int* numbers_size;
};

typedef struct contact_record contact;

contact_name stores the name of the person, numbers is a 2D array of numbers(=strings)(1 row for each type of number), and numbers_size keeps the size of the numbers of each sort.

The tree relevant functions (where the error might occur) are:

Code:

contact init_record(char* contact_name);
void add_number(contact* c, enum number_type numbertype, char* number);
void delete_contact(contact* c);

The implementation of those functions is:

Code:

contact init_record(char* contact_name){
	int i,j;
	contact* c;
	char*** numbers;
	int* numbersize;

	c = (contact*)malloc(sizeof(contact));
	//contactname = malloc(20*sizeof(char));
	numbers = malloc(sizeof(char**));
	for(i=0; i < 3; i++) {
		numbers[i] = malloc(sizeof(char*));
		for(j=0; j < 1; j++)
			numbers[i][j] = malloc(15*sizeof(char));
	}
	numbersize = calloc(3,sizeof(int));

	c->contact_name = contact_name;
	c->numbers = numbers;
	c->numbers_size = numbersize;

	return *c;
}

void add_number(contact* c, enum number_type numbertype, char* number){
	switch(numbertype) {
		case MOBILE:
			c->numbers_size[0]++;
			c->numbers[0] = realloc(c->numbers[0], c->numbers_size[0]*sizeof(char*));
			c->numbers[0][c->numbers_size[0]-1] = number;
			break;
		// same for PRIVATE and HOME
	}
}

void delete_contact(contact* c){
	int i;
	free(c->numbers_size);
	for(i=0; i < 3; i++) {
		free(c->numbers[i]);
	}
	free(c->numbers);
	free(c->contact_name);
	free(c);
}

The error occurs when reaching the line:

Code:

free(c->numbers);

Is there anyone who might have an idea wath I'm doing wrong?
Thanks in advance,

Steven

Code:

	numbers = malloc(sizeof(char**));
	for(i=0; i < 3; i++) {
		numbers[i] = malloc(sizeof(char*));

For numbers you allocate only space for a single pointer.
Kurt

Originally Posted by Salem

> for(j=0; j < 1; j++)
This is only 1 element long, so what's the point of this dimension of the array?

I start with a space for one number of each type, and every time I add a number I reallocate one space extra. (Saving my memory)

Thanks for your help, but my problem isn't solved yet.
the strcpy still gives me the same error.

Someone who might know what the problem is?
Thanks in advance,

Steven

It is not for en embedded system that I am writing this. I justed want to exercise the realloc function.

The c->numbers[0..2] are all allocated in this piece of code

Code:

numbers = malloc(sizeof(char**));
	for(i=0; i < 3; i++) {
		numbers[i] = malloc(sizeof(char*));
		for(j=0; j < 1; j++)
			numbers[i][j] = malloc(15*sizeof(char));
	}

I think this piece is correct.
The tree rows are correctly freed but it's in this line

Code:

free(c->numbers);

that it goes wrong.
This is strange, because the are only 3 rows in the table, and they are all 3 freed correctly.
I don't understand why there is an error at freeing the whole array then.

Steven

Originally Posted by matsp

So is c->numbers the same value when you set it and when you try to free it?
What exactly is the error-message (or mis-behaviour) you get when freeing it?

If you use the debugger in Visual studio, you can probably find out the answer to the first question. If it changes, then you need to find out where this happens...

--
Mats

I have debugged my program and the address in the begin and at the end of the c->numbers are the same. So that's not the problem, I assume.

When I debug, and I try to free the array, I get a Visual C++ window with the text

Code:

Windows has triggered a breakpoint in adressbook.exe.

This may be due to a corruption of the heap, and indicates a bug in adressbook.exe or any of the DLLs it has loaded.

The output window may have more diagnostic information

The output window doesn't show anything extra.

Originally Posted by matsp

Correct me if I'm wrong, but:

Code:

			c->numbers[0][c->numbers_size[0]-1] = number;

changes the pointer allocated here:

Code:

		for(j=0; j < 1; j++)
			numbers[i][j] = malloc(15*sizeof(char));

Where does "number" in the first code snippet come from?

--
Mats

"number" is the string representation of a phone number. It is given as a parameter of the add_number method.

and I think you right,

Code:

c->numbers[0][c->numbers_size[0]-1] = number

gets a new pointer here, but does this matter when freeing the memory, because it is overwritten?

Originally Posted by Salem

From what I can see of your usage so far, a person can have more than one mobile number (for example).
Is this correct?

You are right.
That's an extra feature