I am trying to implement a struct to keep binary data. Just like this:
struct Buffer {
int size_;
int capacity = 1000000;
int beg_index, end_index;
char data_[1000000];
} buffer_audio[3];
And a function to write the binary data in the buffer:
int writing_bufer(Buffer buffers, const char *data, int nbytes) {
if (nbytes == 0) return 0;
int capacity = buffers.capacity;
int bytes_to_write = std::min(nbytes, capacity - buffers.size_);
if (bytes_to_write <= capacity - buffers.end_index)
{
memcpy(buffers.data_ + buffers.end_index, data, bytes_to_write);
buffers.end_index += bytes_to_write;
if (buffers.end_index == capacity) buffers.end_index = 0;
}
else { return 0; }
buffers.size_ += bytes_to_write;
return bytes_to_write;
}
But the problem is.. Every time I run this routine the values of beg_index and end_index are deleted. And the memcpy will overwrite.
The routine:
void buffering_mem(char* chunk,int size_chunk, int close_file, int client, int total_size){
int check_bytes = writing_bufer(buffer_audio[client], chunk, size_chunk);
//other code
}
int writing_bufer(Buffer buffers, const char *data, int nbytes)
should be
int writing_bufer(Buffer& buffers, const char *data, int nbytes)
You copied buffers into the function and filled the local buffers and then destroyed them.
Related
EDIT: Clarification:
If I have an array int* a = new int[10], I want to get a pointer to a, but only the values from 0 to 5, without having to allocate another array for those values.
Original post:
I created a small class to fuzz my functions, but the thing is that it is painfully slow. It takes roughly 10-20 seconds to run my function 1000 times.
I decided to improve my code by allocating a very large array at first, then filling it from 0 to a randomly generated number and then just returning a pointer to that range to use in my function instead of allocating memory and deleting it each time.
Below is my code.
I attempt to allocate 1 million bytes at first, then I want to return a range from 0 to whatever size my class generated. Currently I allocate memory once more for returning it, but that's not efficient.
I use Xorshift to generate random numbers, which should be much faster than rand() so I think besides memory allocation it's pretty good, but any suggestions are very much welcome!
Note: if you do not understand part of my code ask me (it's written quickly, so it might be unintelligible at certain parts) ;)
class fuzz {
public:
fuzz() {
this->alloc_init_buff();
}
~fuzz() {
this->dealloc_init_buff();
}
int fill_buff(unsigned int size) {
if (size > this->m_buffsize) { size = this->m_buffsize; }
for (int i = 0; i < size; ++i) {
this->m_buff[i] = this->rand_xor();
}
return size;
}
int fill_buff() {
int size = this->rand_xor(1, this->m_buffsize);
if (size > this->m_buffsize) { size = this->m_buffsize; }
for (int i = 0; i < size; ++i) {
this->m_buff[i] = this->rand_xor();
}
return size;
}
unsigned char*& get_buff(int size) {
unsigned char* temp = new unsigned char[size];
memcpy((void*)temp, (void*)this->m_buff, size);
return temp;
}
private:
struct xr_xorshift_state {
unsigned int a = 123456789, b = 362436069, c = 521288629, d = 88675123;
};
unsigned int xorshift(xr_xorshift_state* state) {
unsigned int res = 0;
res = state->a ^ (state->a << 11);
state->a = state->b; state->b = state->c; state->c = state->d;
state->d = state->d ^ (state->d >> 19) ^ (res ^ (res >> 8));
res &= 0x7fffffff;
return res;
}
unsigned int rand_xor() {
return this->xorshift(&this->m_state);
}
unsigned int rand_xor(unsigned int min, unsigned int max) {
return (min + (this->rand_xor() % (max - min)));
}
void alloc_init_buff() {
this->m_buff = new unsigned char[this->m_buffsize];
}
void dealloc_init_buff() {
delete[] this->m_buff;
}
xr_xorshift_state m_state = { 0 };
unsigned char* m_buff = { 0 };
unsigned int m_buffsize = { 1000000 };
};
int find_newline(const char* text, int size) {
int pos = 0;
while (*text != '\n') {
if (pos == size) { return 0; }
++text; ++pos;
}
return pos;
}
int main() {
fuzz fz = {};
unsigned char* randdata = nullptr;
int lap = 0;
int th = 0;
for (;;) {
if (lap == 1000) {
lap = 0;
++th;
printf("%d thousand laps done!\n", th);
}
try {
int size = fz.fill_buff();
randdata = fz.get_buff(size);
const char* d = (const char*)randdata;
find_newline(d, size);
delete[] randdata;
++lap;
}
catch (...) {
printf("error!\n");
++lap;
}
}
getchar();
return 0;
}
I came across one strange behaviour. In my code one variable is decremented, but not incremented and as a result my algorithm does not work. The variable name is blocksAvailable, it is defined in Chunk class, initiated with Chunk::init method, decremented with Chunk::allocate method and must be incremented with Chunk::deallocate method. So, there are just two places where this variable is mentioned - allocate and deallocate methods. In one place it gets decremented (and it works) and in other place it gets incremented and it does not work. This is the completely minimized and reproducible code:
#include <cstddef>
#include <iostream>
#include <vector>
using uchar = unsigned char;
class Chunk
{
private:
friend class FixedAllocator;
void init(size_t blockSize, uchar blocks);
void release();
void* allocate(size_t blockSize);
void deallocate(void* p, size_t blockSize);
inline bool hasBlock(void* p, size_t chunkLen) const
{
uchar * pc = static_cast<uchar*>(p);
return (pData <= pc) && (pc <= (pData + chunkLen));
}
inline bool releasable(uchar numBlocks) const
{
return blocksAvailable == numBlocks;
}
uchar* pData;
uchar firstAvailableBlock, blocksAvailable;
};
void Chunk::init(size_t blockSize, uchar blocks)
{
// for n of Ts it will allocate n * sizeof(T) memory
pData = new uchar[blockSize * blocks];
firstAvailableBlock = 0;
blocksAvailable = blocks;
uchar i = 0;
uchar* p = pData;
// used by allocate method to move forward firstAvailableBlock
for (; i != blocks; p += blockSize)
{
*p = ++i;
}
}
void Chunk::release()
{
::operator delete(pData);
}
void* Chunk::allocate(size_t blockSize)
{
if (!blocksAvailable) return 0;
// move firstAvailableBlock one block ahead
uchar* pResult = pData + firstAvailableBlock * blockSize;
firstAvailableBlock = *pResult;
--blocksAvailable;
std::cout << "blocksAvailable after allocate " << blocksAvailable << std::endl;
return pResult;
}
void Chunk::deallocate(void* p, size_t blockSize)
{
uchar* toRelease = static_cast<uchar*>(p);
// find last but one available block
firstAvailableBlock = static_cast<uchar>((toRelease - pData) / blockSize);
++blocksAvailable;
std::cout << "blocksAvailable after deallocate " << blocksAvailable << std::endl;
}
class FixedAllocator
{
private:
size_t blockSize;
uchar blocks;
using Chunks = std::vector<Chunk>;
Chunks chunks;
Chunk* allocChunk;
public:
FixedAllocator();
~FixedAllocator();
void init(size_t blockSize, size_t pageSize);
const int blockOwner(void* p) const;
void * allocate();
void deallocate(void* p);
};
FixedAllocator::FixedAllocator()
:blockSize(0),
blocks(0),
chunks(0),
allocChunk(nullptr)
{
}
FixedAllocator::~FixedAllocator()
{
Chunks::iterator it;
for (it = chunks.begin(); it != chunks.end(); ++it)
{
it->release();
}
}
void FixedAllocator::init(size_t blockSize_, size_t pageSize)
{
blockSize = blockSize_;
size_t numBlocks = pageSize / blockSize;
blocks = static_cast<uchar>(numBlocks);
}
const int FixedAllocator::blockOwner(void* p) const
{
size_t chunkLen = blocks * blockSize;
std::vector<int>::size_type i = 0, sz = chunks.size();
for (; i < sz; i++)
{
if (chunks[i].hasBlock(p, chunkLen))
{
return i;
}
}
return -1;
}
void* FixedAllocator::allocate()
{
if (!allocChunk || allocChunk->blocksAvailable == 0)
{
Chunks::iterator i = chunks.begin();
for (;;++i)
{
if (i == chunks.end())
{
// allocate memory for one more chunk
chunks.reserve(chunks.size() + 1);
Chunk newChunk;
newChunk.init(blockSize, blocks);
// add new chunk to memory pool
chunks.push_back(newChunk);
// points to new just initiated chunk
allocChunk = &chunks.back();
break;
}
if (i->blocksAvailable > 0)
{
// points to chunk with available blocks
allocChunk = &*i;
break;
}
}
}
return allocChunk->allocate(blockSize);
}
void FixedAllocator::deallocate(void* p)
{
// TODO. Optimize. Now very bruteforce and non-efficient
const int chunkPos = blockOwner(p);
if (chunkPos != -1)
{
Chunk chunk = chunks[chunkPos];
chunk.deallocate(p, blockSize);
// if chunk is releasable, release memory
if (chunk.releasable(blocks))
{
chunk.release();
chunks.erase(chunks.begin() + chunkPos);
// allocChunk may point to deleted chunk
// so, reset it
allocChunk = &chunks.back();
} else {
// there are free blocks in chunk
// so, reset allocChunk for faster future allocation
allocChunk = &chunk;
}
}
}
int main() {
FixedAllocator* alloc = new FixedAllocator();
alloc->init(4, 12);
void* p = alloc->allocate();
void* q = alloc->allocate();
void* r = alloc->allocate();
alloc->deallocate(p);
alloc->deallocate(q);
alloc->deallocate(r);
return 0;
}
As you can see, I have two debug statements in my code. One which prints blocksAvailable value after increment and one which prints its value after decrement.
But this is what I have on my screen, when I compile and run my code:
As you can see, blocksAvailable is initiated with value 3, then it gets decremented three times (three calls to allocate method), but after each decrement (call to deallocate) its value stays the same - 1. It really drives me crazy and looks like some ghost in my code. You can easily reproduce it, compile and run as simply as:
$ g++ main.cpp
$ ./a.out
I hope, someone can help me to find where this ghost appeared from.
Here is the only place in your code where you call Chunk::deallocate:
Chunk chunk = chunks[chunkPos];
chunk.deallocate(p, blockSize);
The first line makes a copy of your Chunk; the second line calls deallocate on it, which increments chunk.blocksAvailable. But chunk is just a copy of the data. Modifying it has no lasting effect.
In particular, chunks[chunkPos] is unaffected and still contains blocksAvailable = 0.
For my code, expand is to double the capacity of the vector. It should dynamically reallocate memory for the dynamically allocated array and update the value of capacity while not creating a memory leak.
I was wondering how you would check for a memory leak as my testing doesn't show execution times in Visual Studio.
void IntVector::expand(){
cap = cap * 2;
int *data2;
data2 = data;
IntVector::~IntVector();
data = new int[cap];
data = data2;
delete data2;
}
header (I understand that you aren't supposed to be using namespace std).
#ifndef INTVECTOR_H
#define INTVECTOR_H
using namespace std;
class IntVector{
private:
unsigned sz;
unsigned cap;
int *data;
public:
IntVector();
IntVector(unsigned size);
IntVector(unsigned size, int value);
unsigned size() const;
unsigned capacity() const;
bool empty() const;
const int & at (unsigned index) const;
const int & front() const;
const int & back() const;
~IntVector();
void expand();
};
#endif
main file
#include "IntVector.h"
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
IntVector::IntVector(){
sz = 0;
cap = 0;
data = NULL;
}
IntVector::IntVector(unsigned size){
sz = size;
cap = size;
data = new int[sz];
*data = 0;
}
IntVector::IntVector(unsigned size, int value){
sz = size;
cap = size;
data = new int[sz];
for(int i = 0; i < sz; i++){
data[i] = value;
}
}
unsigned IntVector::size() const{
return sz;
}
unsigned IntVector::capacity() const{
return cap;
}
bool IntVector::empty() const{
if(sz > 0){
return false;
}
else{
return true;
}
}
const int &IntVector::at(unsigned index) const{
if(index > sz){
exit(1);
}
else{
return data[index];
}
}
const int &IntVector::front() const{
return data[0];
}
const int &IntVector::back() const{
return data[sz];
}
IntVector::~IntVector(){
delete data;
}
void IntVector::expand(){
cap = cap * 2;
int *data2;
data2 = data;
IntVector::~IntVector();
data = new int[cap];
data = data2;
delete data2;
}
Edit::
void IntVector::expand(){
cap = cap * 2;
int *data2 = data;
data = new int[cap];
delete[] data2;
delete data2;
}
These 2 lines:
data = new int[cap];
data = data2;
Allocate an array of ints, and then immediately override the pointer leading to it, thereby losing that allocated memory for ever. That's a memory leak.
Using valgrind or similar tools should lead to these errors very easily.
To test for memory leaks in Visual Studio:
#define _CRTDBG_MAP_ALLOC
#include <stdlib.h>
#include <crtdbg.h>
and this next line will automatically display a memory-leak report at every place in your code where an application exit occurs.
_CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF );
Edited for maxywb
I use task manager from windows.
in windows 8:
Details tab -> right click on a column and 'select columns' -> GDI objects
Keep an eye on this column, if this keeps rising while it shouldn't then you have a leak.
I'm trying to understand how to create & handle an array of unsigned char arrays in C++. Such as:
Array[0] = { new array of unsigned chars }
Array[1] = { new array of unsigned chars }
Array[2] = { new array of unsigned chars }
....and so on
I've written the next code but I have the feeling that I'm doing something wrong. The code works correctly, but I don't know if the way I declare the "buffer" and how I delete the cache is the correct way, or if it can produce a memory leak.
#define MAX_BUFFER 10
unsigned char* cache[MAX_BUFFER];
bool cache_full = false;
void AddToCache(unsigned char *buffer, const size_t buffer_size)
{
if (cache_full == true)
{
return;
}
for (int index = 0; index < MAX_BUFFER; index++)
{
if (cache[index] == NULL)
{
cache[index] = new unsigned char[buffer_size];
memcpy(cache[index], buffer, buffer_size);
}
if (index < MAX_BUFFER - 1)
{
cache_full = true;
}
}
}
void ClearCache()
{
for (int index = 0; index < MAX_BUFFER; index++)
{
if (cache[index] != NULL)
{
delete[] cache[index];
cache[index] = NULL;
}
}
cache_full = false;
}
bool IsCacheFull()
{
return cache_full;
}
This works?
memcpy(cache, buffer, buffer_size);
It shouldn't. That's overwriting all the pointers in cache with the contents of buffer. In context, this should probably be:
memcpy(cache[index], buffer, buffer_size);
Also, you'll be setting cache_full to true, repeatedly, every time you add to the cache. Try:
AddToCache(unsigned char *buffer, const size_t buffer_size)
{
for (int index = 0; index < MAX_BUFFER; index++)
{
if (cache[index] == NULL)
{
cache[index] = new unsigned char[buffer_size];
memcpy(cache[index], buffer, buffer_size);
return(index); // in case you want to find it again
}
}
// if we get here, we didn't find an empty space
cache_full = true;
return -1;
}
This question already has answers here:
How to replicate vector in c?
(6 answers)
Closed 2 years ago.
I have a code (C++) that looks like this
vector<int> values[10000];
int i, j;
while (.....) {
scanf("%d%d", &i, &j);
values[i].push_back(j);
values[j].push_back(i);
}
but I want to rewrite this code to C. How can I do this?
I researched the opportunity to make the own stack, but maybe have more lightweight way to rewrite this code, maybe two-dimensional arrays. So far I can not think how this remake, I hope that someone more experienced tell me how to do it :)
Sorry guys, added a more advanced example...
Instead of rolling your own, you may want to try a C container library, e.g. http://code.google.com/p/ccl/
You can use Gena library. It closely resembles stl::vector in pure C89.
You can check it out here:
https://github.com/cher-nov/Gena
Something like this:
#include <stdio.h>
#include <stdlib.h>
typedef struct _darray
{
size_t size;
size_t actual_size;
int *content;
} darray;
void darray_create(darray *d)
{
d->actual_size = d->size = 0;
d->content = NULL;
}
void darray_append(darray *d, int v)
{
if (d->size+1 > d->actual_size)
{
size_t new_size;
if (!d->actual_size)
{
new_size = 1;
}
else
{
new_size = d->actual_size * 2;
}
int *temp = realloc(d->content, sizeof(int) * new_size);
if (!temp)
{
fprintf(stderr, "Failed to extend array (new_size=%zu)\n", new_size);
exit(EXIT_FAILURE);
}
d->actual_size = new_size;
d->content = temp;
}
d->content[d->size] = v;
d->size++;
}
const int* darray_data(darray *d)
{
return d->content;
}
void darray_destroy(darray *d)
{
free(d->content);
d->content = NULL;
d->size = d->actual_size = 0;
}
size_t darray_size(darray *d)
{
return d->size;
}
int main()
{
int i;
darray myarray;
const int *a;
darray_create(&myarray);
for(i = 0; i < 100; i++)
{
darray_append(&myarray, i);
}
a = darray_data(&myarray);
for(i = 0; i < darray_size(&myarray); i++)
{
printf("i=%d, value=%d\n", i, a[i]);
}
darray_destroy(&myarray);
}
You can try something like this:
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct vector
{
int len;
int allocated;
int step;
int *data;
};
#define INIT_SIZE 1
void init_vector(struct vector *v)
{
v->len = 0;
v->allocated = 0;
v->step = 2;
v->data = NULL;
}
int append(struct vector *v, int item)
{
if (!v->data)
{
v->data = malloc(INIT_SIZE * sizeof(int));
if (!v->data)
return -1;
v->allocated = INIT_SIZE;
}
else
if (v->len >= v-vallocated)
{
int *tmp = realloc(v->data,
v->allocated * v->step * sizeof(int));
if (!tmp)
return -1;
v->data = tmp;
v->allocated *= v->step;
}
v->data[v->len] = item;
v->len++;
return 0;
}
int delete(struct vector *v, int index)
{
if (index < 0 || index >= v->len)
return -1;
memmove(v->data + index, v->data + index + 1,
(v->len - index - 1) * sizeof(int));
v->len--;
return 0;
}
void print(const struct vector *v)
{
printf("Array:\n");
for (int i = 0; i < v->len; i++)
printf("%d ", v->data[i]);
printf("\n");
}
int main(void)
{
struct vector v;
int rc;
init_vector(&v);
rc = append(&v, 1);
assert(rc == 0);
rc = append(&v, 2);
assert(rc == 0);
rc = append(&v, 3);
assert(rc == 0);
rc = append(&v, 4);
assert(rc == 0);
rc = append(&v, 5);
assert(rc == 0);
print(&v);
rc = delete(&v, 2);
assert(rc == 0);
print(&v);
free(v.data);
return 0;
}
A rough equivalent of a C++ vector would be a resizing C array (to account for more elements than available).
Ergo, the equivalent of an array of vectors would be an array of pointers (an array of arrays wouldn't cut it because of the resizing constraint).
int* values[1000];
You'll need to account for the sizes though, so you could either do that externally or wrap the logic inside a structure.
int sizes[1000];
int noElements[1000];
// all sizes and noElements initially 0
for (int i = 0; i < 10; i++) {
if ( noElements[i] >= sizes[i] )
{
// allocate more memory for values[i];
// copy old contents into the new memory
// update sizes[i]
}
values[i][noElements] = 10;
noElements++;
}
There is no C standard equivalent to the c++ vector, though you could create a struct based off of the vector in c++. The struct would
Resize itself if the array bounds are passed the max size
perform the operations similar to that of a vector
OR
Create a linked list stack struct that simulates that of a c++ vector
I'm affraid you'll have to work with heap memory in 80's fashion in the plain C.
typedef struct tagArrayDesc {
int* arr;
size_t top;
size_t reserved;
} ArrayDesc;
#define EC(NAME, T) size_t ensure_capacity##NAME##(size_t size, \
T** vec, \
size_t reserved) \
{ \
size_t new_reserved; \
new_reserved = reserved; \
if (reserved < size) { \
if (reserved != 0) { \
new_reserved *= 2; \
} else { \
new_reserved = 0x10; \
} \
} \
if (new_reserved < size) { \
new_reserved = (size * 4) / 3; \
} \
if (new_reserved > reserved) { \
*vec = realloc(*vec, sizeof(**vec) * new_reserved); \
memset((*vec) + reserved, 0, sizeof(T) * (new_reserved - reserved)); \
} \
return new_reserved; \
}
EC(_int, int)
EC(_array_desc, ArrayDesc)
int main()
{
ArrayDesc* rows = NULL;
size_t rows_size = 0;
size_t rows_reserved = 0;
while (true) {
int i, j;
scanf("%d%d", &i, &j);
rows_reserved = ensure_capacity_array_desc(i + 1, &rows, rows_reserved);
rows[i].reserved = ensure_capacity_int(j + 1, &rows[i].arr, rows[i].reserved);
rows[i].arr[j] = 42;
}
return 0;
}
You have to work with dynamic memory allocation. It's not hard. Every time when a new item must be inserted just use realloc. Somethink that looks like this:
#include <cstdlib>
typedef struct { } UserType;
int currentSize = 0;
UserType* values;
/// Add new value to values method
void addValue(const UserType& newValue)
{
++currentSize;
values = static_cast<UserType*>(realloc(values, currentSize));
if (values == NULL)
// memory allocation filed, place fix code here
*(values + currentSize) = newValue;
}
Remember, u have to use free for free memory of the values. Also, you may don't free allocated memory if will end work right now.