The following are two functions in which the first one tries to allocate and subsequently reallocate memory for an array of pointers depending on the count value.
The second function tries to concatenate the last string onwards to the first string from array of pointers.
The program takes in the number of strings and a pattern to be matched as command line arguments and calls the first function only when a matching pattern is found in the input string.
20 char **allocate_array_of_ptrs(char **str_array, /* pointer to the array of pointers */
21 char *str, /* pointer to the input string */
22 int count) /* count of matched strings */
23 {
24 char **temp = NULL; /* temporary pointer to realloc memory */
25
26 /* realloc based on count value */
27 temp = (char **)realloc(str_array, count * sizeof(char *));
28
29 int str_len = strlen(str);
30
31 /* if realloc is successful */
32 if (NULL != temp)
33 {
34 str_array = temp;
35
36 /* alloc memory for the string to be stored */
37 temp[count - 1] = (char *)calloc((str_len + 1), sizeof(char));
38 strcpy(temp[count - 1], str);
39 }
40
41 return str_array;
42 }
43
44 char **dmm_str_cat(char **str_array, /* pointer to the array of pointers */
45 int count) /* count of matched strings */
46 {
47 int i; /* iterator */
48 int total_str_len = 0; /* total length when all strings put together */
49 int str_len_of_first; /* string length of first string in the array */
50
51 if (count > 1)
52 {
53 str_len_of_first = strlen(str_array[0]);
54
55 for (i = 0; i < count; i++)
56 {
57 total_str_len += strlen(str_array[i]);
58 }
59 total_str_len += 1;
60
61 /* realloc memory to accomodate all matched strings onto first string */
62 str_array[0] = (char *)realloc(str_array[0], total_str_len * sizeof(char));
63
64 /* clearing the new allocated bytes */
65 for (i = (str_len_of_first + 1); i < total_str_len; i++)
66 {
67 str_array[0][i] = '\0';
68 }
69
70 /* concatenate from the last string onwards onto first string */
71 for (i = count - 1; i > 0; i--)
72 {
73 strcat(str_array[0], str_array[i]);
74 }
75 }
76
77 return str_array;
78 }
The problem is that when the code is run under valgrind, it reports the following messages when out of 3 strings, 2 strings do not match the pattern 'el'. Similar errors are reported for other combinations.
Enter string 1 : matter
Enter string 2 : matter
Enter string 3 : jello
Count of strings having matching pattern 'el' : 1
The matching strings are :
jello
==6244== Invalid read of size 8
==6244== at 0x400A74: main (dmm_main.c:86)
==6244== Address 0x4C33038 is 0 bytes after a block of size 8 alloc'd
==6244== at 0x4A05809: malloc (vg_replace_malloc.c:149)
==6244== by 0x4A05883: realloc (vg_replace_malloc.c:306)
==6244== by 0x400AE9: allocate_array_of_ptrs (dmm_functions.c:27)
==6244== by 0x4009B6: main (dmm_main.c:64)
==6244==
==6244== Invalid write of size 8
==6244== at 0x400A89: main (dmm_main.c:87)
==6244== Address 0x4C33038 is 0 bytes after a block of size 8 alloc'd
==6244== at 0x4A05809: malloc (vg_replace_malloc.c:149)
==6244== by 0x4A05883: realloc (vg_replace_malloc.c:306)
==6244== by 0x400AE9: allocate_array_of_ptrs (dmm_functions.c:27)
==6244== by 0x4009B6: main (dmm_main.c:64)
The concatenated string is : jello==6244==
==6244== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 4 from 1)
==6244== malloc/free: in use at exit: 0 bytes in 0 blocks.
==6244== malloc/free: 2 allocs, 2 frees, 14 bytes allocated.
==6244== For counts of detected errors, rerun with: -v
==6244== All heap blocks were freed -- no leaks are possible.
But when there are two strings that match the pattern whereas one doesn't match, then there are no errors/leaks reported by valgrind. When all strings match the pattern then definitely lost is being reported.
Taking into account that you've an invalid read followed by an invalid write, I would bet that str_array passed to allocate_array_of_ptrs is not properly initialized-
Actually, message 0 bytes after a block of size 8 alloc'd makes me think that you're overpassing array's size but I can't be 100% sure without main.c code.
Related
I created an function in c as a linked list but i can't understand how convert it to a linked list.
My Question is how to convert an linked list to an dynamic array. This function adds elements to an linked list i want to be able to add elements to an dynamic array. i don't know if the struct blockhead_node is right like i said i'm still learning c. I do not understand dynamic arrays so i'm trying to create an program that uses them so i may understand them better. i want to create an add function that adds elements to the front or end of the list. This is what i have:
//this struct i'm trying to use for dynamic array
struct blockhead_node
{
float x, y;
float dx, dy;
long color;
int size; // slots used so far
int capacity; // total available slots
int *data; // array of integers we're storing
};
//this struct is for the linked list
struct blockhead_node
{
float x,y;
float dx, dy;
long color;
int size;
struct blockhead_node * next;
};
void add(struct blockhead_node ** blockhead_list) // double pointer because we can't modify the list it self
{
while((*blockhead_list)!=NULL)
{
blockhead_list=&(*blockhead_list)->next;
}
(*blockhead_list) = (struct blockhead_node*) malloc(sizeof(struct blockhead_node));
(*blockhead_list)->x = rand()%screen_width + (*blockhead_list)->size;
//(*blockhead_list)->x = 400;
//
//look up how to create an random floating point number
//
(*blockhead_list)->dx = ((float)rand()/(float)(10000));
(*blockhead_list)->y = rand()%screen_height + (*blockhead_list)->size;
(*blockhead_list)->dy = ((float)rand()/(float)(10000));
(*blockhead_list)->size = rand()%100;
(*blockhead_list)->next = NULL;
if((*blockhead_list)->x + (*blockhead_list)->size > screen_width)
{
(*blockhead_list)->x = screen_width - (*blockhead_list)->size;
}
if((*blockhead_list)->y + (*blockhead_list)->size > screen_height)
{
(*blockhead_list)->y = screen_height - (*blockhead_list)->size;
}
}
Using a dynamic array is not much different than using a linked-list. The primary difference is you are responsible for keeping track of size and realloc your data array when size == capacity (or when capacity == 0 for a new stuct).
Other than that you are either allocating per-node with a linked-list, whereas with a dynamic array you can allocate in a more efficient manner by allocating by some multiple of the current capacity when size == capacity. For arrays of completely unknown size you can either start with capacity = 2 or 8 and then either increase by some multiple (e.g. 3/2 or 2, etc..) or some fixed amount (8, 16, etc..) each time a reallocation is needed. I generally just double the current capacity, e.g. starting a 2, reallocating storage in data for 4, 8, 16, 32, ... integers as more numbers are added to data. You can do it any way you like -- as long as you keep track of your size and capacity.
A short example may help. Let's start with just a simple struct where data is the only dynamic member we are concerned about. For example:
#define CAP 2 /* initial capacity for new struct */
typedef struct {
size_t size,
capacity;
int *data;
} blkhd_node;
Where size is your "slots used so far" and capacity is your "total available slots" and data your "array of integers we're storing".
The add function is fairly trivial. All you need to do is check whether you need to realloc (e.g. this is a struct not used yet where capacity == 0 or all the slots are used and size == capacity). Since realloc can be used for both new and resizing the allocation, it is all you need. The scheme is simple, if this is a new struct, we will allocate for CAP number of int, otherwise if size == capacity we will allocated 2 * capacity number of int.
Whenever we realloc we do so with a temporary pointer! Why? When realloc fails it returns NULL. If you realloc with the original pointer (e.g. data = realloc (data, newsize); and NULL is returned, you overwrite your original pointer address for data with NULL and your ability to reach (or free) the original block of memory is lost -- creating a memory leak. By using a temporary pointer, we can validate whether realloc succeeds before we assign the new address to data. Importantly, if realloc does fail -- then our existing integers pointed to by data are still fine, so we are free to use our original allocation in the event of realloc failure. Important to remember.
We also need a way to indicate success/failure of or add function. Here, you are not adding a new node, so returning a pointer to a new node isn't an option. In this case a simple int return of 0 for failure of 1 for success is just as good as anything else.
With that, an add function could be as simple as:
int add (blkhd_node *b, int v)
{
/* realloc if (1) new struct or (2) size == capacity */
if (!b->capacity || b->size == b->capacity) {
size_t newsize;
if (!b->capacity) /* new stuct, set size = CAP */
newsize = CAP;
else if (b->size == b->capacity) /* otherwise double size */
newsize = b->capacity * 2;
/* alway realloc with a temporary pointer */
void *tmp = realloc (b->data, newsize * sizeof *b->data);
if (!tmp) { /* validate reallocation */
perror ("realloc_b->data");
return 0; /* return failure */
}
b->data = tmp; /* assign new block of mem to data */
b->capacity = newsize; /* set capacity to newsize */
}
b->data[b->size++] = v; /* set data value to v */
return 1; /* return success */
}
Note: since you are initializing your struct and both size and capacity will be 0, you can dispense with separate checks for capacity == 0 and size == capacity and use a ternary to set newsize. This is arguably the less-readable way to go and a good compiler will optimize both identically, but for sake of completeness, you could replace the code setting newsize with:
/* realloc if (1) new struct or (2) size == capacity */
if (b->size == b->capacity) {
/* set newsize */
size_t newsize = b->capacity ? b->capacity * 2 : CAP;
Given the option, your choice should always be for the more readable and maintainable code. You do your job, and let the compiler worry about the rest.
(you can do a dynamic array of struct blockhead_node in exactly the same way -- just account for the number of structs you have in the array in addition to the size, capacity for data in each -- that is left to you)
So, let's see if our scheme of originally allocating for 2-int will allow us to add 100-int to our data array with a short example putting it altogether:
#include <stdio.h>
#include <stdlib.h>
#define CAP 2 /* initial capacity for new struct */
typedef struct {
size_t size,
capacity;
int *data;
} blkhd_node;
int add (blkhd_node *b, int v)
{
/* realloc if (1) new struct or (2) size == capacity */
if (!b->capacity || b->size == b->capacity) {
size_t newsize;
if (!b->capacity) /* new stuct, set size = CAP */
newsize = CAP;
else if (b->size == b->capacity) /* otherwise double size */
newsize = b->capacity * 2;
/* alway realloc with a temporary pointer */
void *tmp = realloc (b->data, newsize * sizeof *b->data);
if (!tmp) { /* validate reallocation */
perror ("realloc_b->data");
return 0; /* return failure */
}
b->data = tmp; /* assign new block of mem to data */
b->capacity = newsize; /* set capacity to newsize */
}
b->data[b->size++] = v; /* set data value to v */
return 1; /* return success */
}
void prndata (blkhd_node *b)
{
for (size_t i = 0; i < b->size; i++) {
if (i && i % 10 == 0)
putchar ('\n');
printf (" %3d", b->data[i]);
}
putchar ('\n');
}
int main (void) {
blkhd_node b = { .size = 0 }; /* declare/initialize struct */
for (int i = 0; i < 100; i++) /* add 100 data values */
if (!add (&b, i + 1))
break; /* don't exit, all prior data still good */
/* output results */
printf ("\nsize : %zu\ncapacity : %zu\n\n", b.size, b.capacity);
prndata (&b);
free (b.data); /* don't forget to free what you allocate */
return 0;
}
Example Use/Output
$ ./bin/dynarrayint
size : 100
capacity : 128
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
Memory Use/Error Check
In any code you write that dynamically allocates memory, you have 2 responsibilities regarding any block of memory allocated: (1) always preserve a pointer to the starting address for the block of memory so, (2) it can be freed when it is no longer needed.
It is imperative that you use a memory error checking program to insure you do not attempt to access memory or write beyond/outside the bounds of your allocated block, attempt to read or base a conditional jump on an uninitialized value, and finally, to confirm that you free all the memory you have allocated.
For Linux valgrind is the normal choice. There are similar memory checkers for every platform. They are all simple to use, just run your program through it.
$ valgrind ./bin/dynarrayint
==12589== Memcheck, a memory error detector
==12589== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==12589== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==12589== Command: ./bin/dynarrayint
==12589==
size : 100
capacity : 128
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
==12589==
==12589== HEAP SUMMARY:
==12589== in use at exit: 0 bytes in 0 blocks
==12589== total heap usage: 7 allocs, 7 frees, 1,016 bytes allocated
==12589==
==12589== All heap blocks were freed -- no leaks are possible
==12589==
==12589== For counts of detected and suppressed errors, rerun with: -v
==12589== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Always confirm that you have freed all memory you have allocated and that there are no memory errors.
Look things over and let me know if you have further questions.
I've written this program to calculate the prime numbers up to len using Eratosthenes method. The program works fine and I can even calculate up to very large numbers like 999,999 and so on and I get a fine output. But the issue is that valgrind always shows me errors, no matter how small or how big len is.
Program:
#include <stdio.h>
#include <stdlib.h>
int main(){
size_t len=100;
int *array=malloc(len * sizeof(*array));
// initialize all elements to 1
for(int i=0;i<len;i++)
array[i]=1;
//set multiples of array[a] to 0
for(int a=2;a<len;a++){
for(int b=2;b<len;b++){
if(a*b>len)
break;
array[a*b]=0;
}
}
//print the index of "1"s in the array
for(int a=2;a<=len;a++){
if(array[a]==1)
printf("%d ", a);
}
printf("\n");
free(array);
return 0;
}
Errors:
I compile using: gcc -std=c99 -Wall -g test.c -o test
Output: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
gdb shows no errors or malfunction
valgrind ./test shows:
==10134== Invalid write of size 4
==10134== at 0x400695: main (...)
==10134== Address 0x52041d0 is 0 bytes after a block of size 400 alloc'd
==10134== at 0x4C2DB8F: malloc (...)
==10134== by 0x400625: main (...)
==10134==
==10134== Invalid read of size 4
==10134== at 0x4006D9: main (...)
==10134== Address 0x52041d0 is 0 bytes after a block of size 400 alloc'd
==10134== at 0x4C2DB8F: malloc (...)
==10134== by 0x400625: main (...)
==10134==
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
==10134==
==10134== HEAP SUMMARY:
==10134== in use at exit: 0 bytes in 0 blocks
==10134== total heap usage: 2 allocs, 2 frees, 1,424 bytes allocated
==10134==
==10134== All heap blocks were freed -- no leaks are possible
==10134==
==10134== For counts of detected and suppressed errors, rerun with: -v
==10134== ERROR SUMMARY: 8 errors from 2 contexts (suppressed: 0 from 0)
As you can see in the code, I am declaring my array as int *array=malloc(len * sizeof(*array)); which seems to me to be the problem. If I declare it like this: int array[len];, valgrind doesn't show me error for small numbers of len, which is also something that fascinates me. Higher numbers of len with VLA declaration causes some unexpected behavior. So what is happening here? Is there anything wrong with the code or can I simply ignore the valgrind errors, since the output is ok? Also, as I said earlier, the program works fine for very large numbers like 999,999 but running valgrind for that len gives exactly 999,999 errors in valgrind. Any explanation is highly appreciated :)
Your malloc is correct, sizeof(*array) is the same as sizeof(int), because *array is an int.
for(int a=2;a<=len;a++) overflows array because array[len-1] is the last element in the array and eventually you do
if(array[a]==1)
printf("%d ", a);
with a==100 which is out of bounds.
It should be
for(int a=2;a<len;a++)
if(array[a] == 1)
printf("%d ", a);
Edit
As Jonathan Leffler has pointed out in the comments,
if(a*b>len)
break;
if also wrong. For a==2 and b==50 you have a*b==100 which is not greater
than len and you are accessing out of bounds again. The condition should be
if(a*b >= len)
break;
Just two comments about your code:
The algorithm implemented here is not exactly the algorithm known as The sieve of Erathostenes, because if you analyse your code you'll see that you have two loops, running all possible values of a and b and marking them as compound. Yes, you finish with a sieve... but that was not the efficient one from Erathostenes. The sieve of Erathostenes consists in getting the next unmarked element, and mark all elements that are multiples of it (until you reach the maximum index, at len) this is something like:
#include <stdio.h>
#include <stdlib.h>
#define N 10000
#define sqrt_N 100
int array[N];
int main(){
int a, b;
/* better to leave them at 0 and marking with ones */
// initialize all elements to 1
//for(int i=0;i<len;i++)
//array[i]=1;
//set multiples of a to 1
/* We only need to do this upto sqrt_N because if a unmarked number
* is discovered above sqrt_N it will be marked (as compund) because
* it was the product of a number less than sqrt_N or be prime (because
* it cannot be the product of two numbers greater than the sqrt(N)
* or it would be greater than N. */
for(a = 2; a < sqrt_N; a++){
if (array[a] == 0) { /* do the inner loop only if a is a prime */
for(b = 2; a * b < N; b++)
array[a * b] = 1;
}
}
//print the index of "0"s in the array
for(a = 2; a <= N; a++){
if(!array[a])
printf("%s%d", a == 2 ? "" : ", ", a);
}
printf("\n");
//free(array); /* array is no more dynamic */
return 0;
}
just check the computation time and you'll see it runs faster than yours.
The problem you are having with a declaration like this:
int sieve[999999];
is that, if you put that as a local variable on main() (as you do) it is going to be stored in the stack, so that means you need at least one million integers (of size 4, most probably) and this is four megabytes in the stack. I don't actually know the operating system you are using, but it is common that the stack size is limited (in the order of 4-10 Mb) so you can overflow the stack if you are not careful with the size of your automatic variables.
The invalid write message from valgrind(1) comes from the fact that you have written the following code:
if (a*b > len) break;
and that means that, in the possible case that a*b results exactly len, you are writing in the array cell array[len] which is outside of the bounds of array (by one, they go from 0 to len - 1) You have to change that line to read:
if (a*b >= len) break;
or
if (a*b < len) {
array[a*b] = 0;
}
Please help me understand - why am I getting this run-time error:
*** stack smashing detected ***:
Program received signal SIGABRT, Aborted.
for the following code :
#define WORD_SIZE (sizeof(int))
#define FLOOR_MASK 0xfffffffc
static void SetVal(void* _block, int _size)
{
*(int*)_block = _size;
}
void BufferInit(void* _buffer, size_t _totalSize)
{
int alignedSize;
assert(_buffer);
/* align _totalSize to be WORD_SIZE multiple */
alignedSize = _totalSize & FLOOR_MASK;
/* mark end of buffer */
SetVal(_buffer + alignedSize, END_VAL);
}
int main()
{
Byte buffer[36];
BufferInit(buffer, 37);
return 0;
}
P.S: The error occurs at the end of the run (on line "return 0;" ).
Thanks.
The SetVal() function writes to 4 bytes to the location you have indicated as the end. That is:
BufferInit(buffer, 37);
... Leads to ...
SetVal(_buffer + alignedSize, END_VAL);
... which does ...
*(int*)_block = _size;
alignedSize is 36 (37 & ~3 = 36) [~3 = 0xFFFFFFFC]. 4 bytes at offset 36 writes to bytes 36, 37, 38 and 39. Since your buffer originally is 36 bytes long, it's outside of your buffer. Either change your buffer to be 40 bytes long, or change your 37 to be 33 [or a lower number].
Stupid mistake..
I exceeded buffer's size:
alignedSize [= buffer size] = 36
bytes allocated for buffer: 0-35
I'm changing (buffer+36) = buffer[36] which is beyond buffer's memory limit.
Fixed code:
SetVal(_buffer + alignedSize - WORD_SIZE, END_VAL);
I have written below sample program in 'C' which is dynamic memory intensive and tried to benchmark the same (in terms of time taken) for the 'glibc' default allocator versus Hoard allocator.
1 #include <stdio.h>
2 #include <stdlib.h>
3
4 #define NUM_OF_BLOCKS (1 * 4096)
5
6 void *allocated_mem_ptr_arr[NUM_OF_BLOCKS];
7
8 int
9 main (int argc, char *argv[])
10 {
11 void *myblock = NULL;
12
13 int count, iter;
14
15 int blk_sz;
16
17 if (argc != 2)
18 {
19 fprintf (stderr, "Usage:./memory_intensive <Block size (KB)>\n\n");
20 exit (-1);
21 }
22
23 blk_sz = atoi (argv[1]);
24
25 for (iter = 0; iter < 1024; iter++)
26 {
27 /*
28 * The allocated memory is not accessed (read/write) hence the residual memory
29 * size remains low since no corresponding physical pages are being allocated
30 */
31 printf ("\nCurrently at iteration %d\n", iter);
32 fflush (NULL);
33
34 for (count = 0; count < NUM_OF_BLOCKS; count++)
35 {
36 myblock = (void *) malloc (blk_sz * 1024);
37 if (!myblock)
38 {
39 printf ("malloc() fails\n");
40 sleep (30);
41 return;
42 }
43
44 allocated_mem_ptr_arr[count] = myblock;
45 }
46
47 for (count = 0; count < NUM_OF_BLOCKS; count++)
48 {
49 free (allocated_mem_ptr_arr[count]);
50 }
51 }
52 }
As a result of this benchmark activity, I got below results (Block Size, Time elapsed for default allocator, Time elapsed for Hoard):
'1K' '4.380s' '0.927s'
'2k' '8.390s' '0.960s'
'4k' '16.757s' '1.078s'
'8k' '16.619s' '1.154s'
'16k' '17.028s' '13m 6.463s'
'32k' '17.755s' '5m 45.039s'
As can be seen, Hoard performance severely degrades with block size >= 16K. What is the reason? Can we say that Hoard is not meant for applications allocating large size chunks?
There are some nice benchmarks and explanations at http://locklessinc.com/benchmarks_allocator.shtml:
For small allocaitons, it still performs similarly to tcmalloc. However, beyond about 64KiB, it drops drastically in performance. It uses a central "hoard" to redistribute memory between threads. This presents a bottle-neck as only one thread at a time can be using it. As the number of threads increases, the problem gets worse and worse.
For the following sample of code there is memory leak. How can we prevent memory leak in the following case:
1 #include <stdio.h>
2 #include <stdlib.h>
3
4 typedef struct sample_help {
5 int *value;
6 void **pointers;
7 }*sample,sample_node;
8
9
10 sample main(){
11 sample ABC=NULL;
12 sample XYZ=NULL;
13 sample kanchi = NULL;
14
15 ABC = malloc(sizeof(sample_node));
16 XYZ = malloc(sizeof(sample_node));
17 ABC->pointers = malloc(5*sizeof(void *));
18 XYZ->pointers = malloc(5*sizeof(void *));
19 ABC->value = malloc(5*sizeof(int));
20 XYZ->value = malloc(5*sizeof(int));
21
22 ABC->value[0] = 10;
23 ABC->value[1] = 20;
24
25 XYZ->pointers[0] = ABC;
26 kanchi = XYZ->pointers[0];
27
28 printf("::::%d\n",XYZ->pointers[0]);
29 printf("kanchi1:::::%d\n",kanchi->value[0]);
30
31
32 return XYZ;
33 }
34
Following is the output of valgrind.
==27448==
==27448== HEAP SUMMARY:
==27448== in use at exit: 152 bytes in 6 blocks
==27448== total heap usage: 6 allocs, 0 frees, 152 bytes allocated
==27448==
==27448== 152 (16 direct, 136 indirect) bytes in 1 blocks are definitely lost in loss record 6 of 6
==27448== at 0x4C244E8: malloc (vg_replace_malloc.c:236)
==27448== by 0x40056B: main (test2.c:16)
==27448==
==27448== LEAK SUMMARY:
==27448== definitely lost: 16 bytes in 1 blocks
==27448== indirectly lost: 136 bytes in 5 blocks
==27448== possibly lost: 0 bytes in 0 blocks
==27448== still reachable: 0 bytes in 0 blocks
==27448== suppressed: 0 bytes in 0 blocks
==27448==
Your code should really be more like this:
#include <stdio.h>
#include <stdlib.h>
typedef struct sample_help {
int *value;
void **pointers;
} *sample, sample_node;
sample foo(void)
{
sample ABC=NULL;
sample XYZ=NULL;
sample kanchi = NULL;
ABC = malloc(sizeof(sample_node));
XYZ = malloc(sizeof(sample_node));
ABC->pointers = malloc(5*sizeof(void *));
XYZ->pointers = malloc(5*sizeof(void *));
ABC->value = malloc(5*sizeof(int));
XYZ->value = malloc(5*sizeof(int));
ABC->value[0] = 10;
ABC->value[1] = 20;
XYZ->pointers[0] = ABC;
kanchi = XYZ->pointers[0];
printf("::::%d\n",XYZ->pointers[0]);
printf("kanchi1:::::%d\n",kanchi->value[0]);
return XYZ;
}
int main(void)
{
// call your function
sample xyz = foo();
// ... do something with the data structure xyz ...
// free memory allocated by your function
free(xyz->pointers[0]->value); // free ABC->value
free(xyz->pointers[0]->pointers); // free ABC->pointers
free(xyz->pointers[0]); // free ABC
free(xyz->value); // free XYZ->value
free(xyz->pointers); // free XYZ->pointers
free(xyz); // free XYZ
return 0;
}
Note that we free the data structure from within main() after we're done with it.
Just free the used memory when it's no longer needed:
free(ABC->value);
free(XYZ->value);
free(ABC->pointers);
free(XYZ->pointers);
free(ABC);
free(XYZ);
Btw: When this is the whole program, it wouldn't actually matter. Since the OS reclaims all unfreed memory when a process is ended, memory that is in use until the termination of the programm is not required to be freed. However, it is good practice.
Having now read your update in the comments, your module (not called main()) that allocates and returns the memory is fine.
Whatever module uses the value returned from your module, needs to free the data after use. So if you implement your module as
sample mymodule(void)
{
sample foo = malloc(10);
/* set up contents of foo as required */
return foo;
}
Then the caller of mymodule would go like this:
int main (int argc, char *argv[])
{
sample bar = mymodule();
/* use contents of bar as required */
free(bar);
return 0;
}