malloc / free for resizing array
Question
Queue.cpp
#include "Queue.h"
#include "Log.h"
void Queue::resize(int n)
{
Log("[Resize] Req: %d ", n);
DATA_TYPE *temp = (DATA_TYPE *) malloc(sizeof(DATA_TYPE) * n);
int i, j;
for(i = f, j = 0; i < r; i++, j++)
*(temp + j) = *(buffer + i);
Log("Buf: %p ", buffer);
free(buffer);
buffer = temp;
_buf_len = n;
r = r - f;
f = 0;
Log("Buf new: %p \n", buffer);
}
void Queue::enqueue(DATA_TYPE c)
{
if(N == _buf_len)
resize(N * 2);
buffer[r++] = c;
N++;
Log("[Enqueue] D: %d N: %d BUF_LEN: %d \n", c, N, _buf_len);
}
DATA_TYPE Queue::dequeue(void)
{
DATA_TYPE c = buffer[f++];
N--;
if(N > 0 && N == _buf_len / 4)
N / 2 == 0 ? resize(1) : resize( N / 2);
Log("[Dequeue] D: %d N: %d BUF_LEN: %d \n", c, N, _buf_len);
return c;
}
DATA_TYPE Queue::peek(void)
{
return buffer[f];
}
bool Queue::isempty(void)
{
return r == f;
}
int Queue::size(void)
{
return N;
}
Queue::Queue(int n)
{
buffer = (DATA_TYPE *) malloc(sizeof(DATA_TYPE) * n);
f = r = 0;
N = 0;
_buf_len = n;
}
Queue::Queue()
{
buffer = (DATA_TYPE *) malloc(sizeof(DATA_TYPE));
f = r = 0;
N = 0;
_buf_len = 1;
}
Queue::~Queue()
{
free(buffer);
}
Queue.h
#ifndef QUEUE_H
#define QUEUE_H
#include <stdlib.h>
typedef int DATA_TYPE;
class Queue
{
public:
Queue(int);
Queue();
~Queue();
void enqueue(DATA_TYPE);
DATA_TYPE dequeue(void);
bool isempty(void);
DATA_TYPE peek(void);
int size(void);
private:
int N;
int _buf_len;
int f;
int r;
DATA_TYPE *buffer;
void resize(int);
};
#endif
Log.h
#ifndef LOG_H
#define LOG_H
#include "stdio.h"
#include "stdarg.h"
#define DEBUG
void Log(const char *, ...);
#endif
Log.cpp
#include "Log.h"
void Log(const char *frmt, ...)
{
#ifdef DEBUG
va_list ap;
va_start(ap, frmt);
vprintf(frmt, ap);
va_end(ap);
#endif
}
main.cpp
#include "Queue.h"
#include "stdio.h"
#include "ctype.h"
#include "string.h"
int main(int argc, char *argv[])
{
Queue queue;
++argv;
//--argc;
while(--argc > 0)
{
if(strcmp(*argv, "-") != NULL)
queue.enqueue(atoi(*argv));
else
if(!queue.isempty())
queue.dequeue();//printf("%d\n", queue.dequeue());
++argv;
}
printf("\nItems left on queue: %d\n", queue.size());
return 0;
}
The above mention code while running with
./a.out 12 23 34 56 11 22 33 44 55 66 77 88 - - - 34 56 - - - 123 67 56 78 - - 45 - 78 - 23 - 1256 - - 4
[Enqueue] D: 12 N: 1 BUF_LEN: 10 <br>
[Enqueue] D: 23 N: 2 BUF_LEN: 10 <br>
[Enqueue] D: 34 N: 3 BUF_LEN: 10 <br>
[Enqueue] D: 56 N: 4 BUF_LEN: 10 <br>
[Enqueue] D: 11 N: 5 BUF_LEN: 10 <br>
[Enqueue] D: 22 N: 6 BUF_LEN: 10 <br>
[Enqueue] D: 33 N: 7 BUF_LEN: 10 <br>
[Enqueue] D: 44 N: 8 BUF_LEN: 10 <br>
[Enqueue] D: 55 N: 9 BUF_LEN: 10 <br>
[Enqueue] D: 66 N: 10 BUF_LEN: 10 <br>
[Resize] Req: 20 Buf: 0xb7f010 Buf new: 0xb7f030 <br>
[Enqueue] D: 77 N: 11 BUF_LEN: 20 <br>
[Enqueue] D: 88 N: 12 BUF_LEN: 20 <br>
[Dequeue] D: 12 N: 11 BUF_LEN: 20 <br>
[Dequeue] D: 23 N: 10 BUF_LEN: 20 <br>
[Dequeue] D: 34 N: 9 BUF_LEN: 20 <br>
[Enqueue] D: 34 N: 10 BUF_LEN: 20 <br>
[Enqueue] D: 56 N: 11 BUF_LEN: 20 <br>
[Dequeue] D: 56 N: 10 BUF_LEN: 20 <br>
[Dequeue] D: 11 N: 9 BUF_LEN: 20 <br>
[Dequeue] D: 22 N: 8 BUF_LEN: 20 <br>
[Enqueue] D: 123 N: 9 BUF_LEN: 20 <br>
[Enqueue] D: 67 N: 10 BUF_LEN: 20 <br>
[Enqueue] D: 56 N: 11 BUF_LEN: 20 <br>
[Enqueue] D: 78 N: 12 BUF_LEN: 20 <br>
[Dequeue] D: 97 N: 11 BUF_LEN: 20 <br>
[Dequeue] D: 0 N: 10 BUF_LEN: 20 <br>
[Enqueue] D: 45 N: 11 BUF_LEN: 20 <br>
[Dequeue] D: 12 N: 10 BUF_LEN: 20 <br>
[Enqueue] D: 78 N: 11 BUF_LEN: 20 <br>
[Dequeue] D: 23 N: 10 BUF_LEN: 20 <br>
[Enqueue] D: 23 N: 11 BUF_LEN: 20 <br>
[Dequeue] D: 77 N: 10 BUF_LEN: 20 <br>
[Enqueue] D: 1256 N: 11 BUF_LEN: 20 <br>
[Dequeue] D: 88 N: 10 BUF_LEN: 20 <br>
[Dequeue] D: 34 N: 9 BUF_LEN: 20 <br>
[Enqueue] D: 4 N: 10 BUF_LEN: 20 <br>
Items left on queue: 10
*** glibc detected *** ./a.out: free(): invalid next size (fast): 0x0000000000b7f030 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7e626)[0x7fc65d098626]
./a.out[0x400bac]
./a.out[0x400c88]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7fc65d03b76d]
./a.out[0x4006c9]
======= Memory map: ========
00400000-00402000 r-xp 00000000 08:06 1969214 /home/mohit/learnc/algoritms/a.out
00601000-00602000 r--p 00001000 08:06 1969214 /home/mohit/learnc/algoritms/a.out
00602000-00603000 rw-p 00002000 08:06 1969214 /home/mohit/learnc/algoritms/a.out
00b7f000-00ba0000 rw-p 00000000 00:00 0 [heap]
7fc65cd20000-7fc65ce19000 r-xp 00000000 08:06 2756166 /lib/x86_64-linux-gnu/libm-2.15.so
7fc65ce19000-7fc65d018000 ---p 000f9000 08:06 2756166 /lib/x86_64-linux-gnu/libm-2.15.so
7fc65d018000-7fc65d019000 r--p 000f8000 08:06 2756166 /lib/x86_64-linux-gnu/libm-2.15.so
7fc65d019000-7fc65d01a000 rw-p 000f9000 08:06 2756166 /lib/x86_64-linux-gnu/libm-2.15.so
7fc65d01a000-7fc65d1cd000 r-xp 00000000 08:06 2756134 /lib/x86_64-linux-gnu/libc-2.15.so
7fc65d1cd000-7fc65d3cc000 ---p 001b3000 08:06 2756134 /lib/x86_64-linux-gnu/libc-2.15.so
7fc65d3cc000-7fc65d3d0000 r--p 001b2000 08:06 2756134 /lib/x86_64-linux-gnu/libc-2.15.so
7fc65d3d0000-7fc65d3d2000 rw-p 001b6000 08:06 2756134 /lib/x86_64-linux-gnu/libc-2.15.so
7fc65d3d2000-7fc65d3d7000 rw-p 00000000 00:00 0
7fc65d3d7000-7fc65d3ec000 r-xp 00000000 08:06 2756155 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fc65d3ec000-7fc65d5eb000 ---p 00015000 08:06 2756155 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fc65d5eb000-7fc65d5ec000 r--p 00014000 08:06 2756155 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fc65d5ec000-7fc65d5ed000 rw-p 00015000 08:06 2756155 /lib/x86_64-linux-gnu/libgcc_s.so.1
7fc65d5ed000-7fc65d6cf000 r-xp 00000000 08:06 3678116 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16
7fc65d6cf000-7fc65d8ce000 ---p 000e2000 08:06 3678116 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16
7fc65d8ce000-7fc65d8d6000 r--p 000e1000 08:06 3678116 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16
7fc65d8d6000-7fc65d8d8000 rw-p 000e9000 08:06 3678116 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16
7fc65d8d8000-7fc65d8ed000 rw-p 00000000 00:00 0
7fc65d8ed000-7fc65d90f000 r-xp 00000000 08:06 2756114 /lib/x86_64-linux-gnu/ld-2.15.so
7fc65dae6000-7fc65daeb000 rw-p 00000000 00:00 0
7fc65db0b000-7fc65db0f000 rw-p 00000000 00:00 0
7fc65db0f000-7fc65db10000 r--p 00022000 08:06 2756114 /lib/x86_64-linux-gnu/ld-2.15.so
7fc65db10000-7fc65db12000 rw-p 00023000 08:06 2756114 /lib/x86_64-linux-gnu/ld-2.15.so
7fff2987b000-7fff2989c000 rw-p 00000000 00:00 0 [stack]
7fff299b0000-7fff299b1000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
Aborted
Question: Why I'm getting this error when ~Queue() has been called for free(buffer)
I have edited the original question which was "delete buffer instead of free(buffer)".
2 answers
solution1
1 2013-03-26 06:00:46
Your error is stemming from the fact that you're mixing calls to malloc with calls to delete .
Solution: Everything you allocate with malloc , you deallocate with free . Everything you create with new you destroy with delete . If you mix and match you get undefined behavior, which most assuredly means bugs and errors, as you have witnessed here.
Try this instead:
free(buffer);
solution2
1 2013-03-26 08:42:53
I got my problem solved. It's a Logical error. Using Valgrind i got the root cause. Issue: function enqueue() has logical error during (N == _buf_len), i need to add one more conditon (N == _buf_len || r == _buf_len).
eg When Buf_len = 8 (malloc for 32 bytes), r = 8, n = 5, and if enqueue has been called again, I tried to insert the object at boundary ie buffer[8]. and when at destructor, I tried to free the block, it points to memory outside which was allocated by malloc.
void Queue::enqueue(DATA_TYPE c)
{
if(N == 0)
resize(1);
else
if(N == _buf_len || r == _buf_len)
resize(N * 2);
buffer[r++] = c;
N++;
Log("[Enqueue] D: %d N: %d BUF_LEN: %d R: %d F: %d BUFFER: %p\n", c, N, _buf_len, r, f, buffer);
}
DATA_TYPE Queue::dequeue(void) { DATA_TYPE c = buffer[f++]; N--; if(N > 0 && N == _buf_len / 4) _buf_len / 2 == 0 ? resize(1) : resize( _buf_len / 2); Log("[Dequeue] D: %d N: %d BUF_LEN: %d R: %d F: %d BUFFER: %p\n", c, N, _buf_len, r, f, buffer); return c; }
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.
Related Question
new, delete ,malloc & free
malloc and free memory leakage
New, delete, malloc, free
Malloc and free multiple pointers
How are malloc and free implemented?
Using malloc/free with classes
Not able to free memeory allocated by Malloc in
malloc/free based STL allocator
Error with free function after malloc
Free memory after malloc in a loop
Related Tags