Consider this snippet:
#include <vector>
#include <algorithm>
#include <boost/function.hpp>
#include <boost/bind.hpp>
template<typename PODType>
class SomeClass
{
public:
SomeClass() : m_pred(boost::bind(&SomeClass<PODType>::someMethodA, this, _1))
{
}
bool someMethodA(const PODType& elem)
{
return false;
}
bool someMethodB(const std::vector<PODType>& vec)
{
return (std::find_if(vec.begin(), vec.end(), m_pred(_1)) != vec.end());
}
private:
boost::function<bool(PODType)> m_pred;
};
int main(int argc, char* argv[])
{
SomeClass<int> obj;
std::vector<int> v;
obj.someMethodB(v);
return 0;
}
The compiler gives
error: no match for call to '(boost::function<bool(int)>) (boost::arg<1>&)'
note: no known conversion for argument 1 from 'boost::arg<1>' to 'int'
for the line return (std::find_if(vec.begin(), vec.end(), m_pred(_1)));
I'm trying to call someMethodA within the member predicate for the find_if calls.
Just pass m_pred, no need for m_pred(_1).
Related
#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;
struct hashfunction{
size_t operator()(pair<string,int> x){
size_t ret=5381;
for(int i=0;i<x.first.length();i++){
ret=(ret<<5)+(ret)+x.first[i];
}
ret+=x.second;
return ret;
}
};
unordered_set<pair<string,int>,hashfunction> myset;
int main(void)
{
string a="123";
int b= 4;
myset.insert({a,b});
}
I am studying unordered_set and hashfunction. But the code above is not compilable. why not? Anyone can explain why it is not compilable and how to solve this problem?
const is needed after operator()(pair<string,int> x).
I have a class "PclProc" and I want to use std::sort.
I write a compare function in the same class because this comparing need the "in_ptr" which is a variable in the same class.
But as I did as following, there is always an error:
error: no matching function for call to
‘sort(std::vector::iterator, std::vector::iterator,
)’
std::sort(cloud_indice.indices.begin(),cloud_indice.indices.end(),PclProc::MyCompare);
bool PclProc::MyCompare(int id1, int id2)
{
return in_ptr->points[id1].z<in_ptr->points[id2].z;
}
float PclProc::MedianZDist(pcl::PointIndices cloud_indice)
{
std::sort(cloud_indice.indices.begin(),cloud_indice.indices.end(),PclProc::MyCompare);
int size=cloud_indice.indices.size();
float median_x,median_y;
...
Example of a functor being used for std::sort. vector D is the data, vector I is the indices to D. I is sorted according to D with std::sort using the functor. std::sort only creates one instance of class lessthan, then uses that one instance for all of the compares.
#include <algorithm>
#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <vector>
typedef unsigned int uint32_t;
#define SIZE 16
class example{
public:
std::vector<uint32_t> D; // data
std::vector<uint32_t> I; // indices
example(void)
{
D.resize(SIZE);
I.resize(SIZE);
for(uint32_t i = 0; i < SIZE; i++){
D[i] = rand()%100;
I[i] = i;
}
}
void displaydata(void)
{
for(size_t i = 0; i < SIZE; i++)
std::cout << std::setw(3) << D[I[i]];
std::cout << std::endl;
}
class lessthan // lessthan functor for std::sort
{
public:
const example &x;
lessthan(const example &e ) : x(e) { }
bool operator()(const uint32_t & i0, const uint32_t & i1)
{
return x.D[i0] < x.D[i1];
}
};
void sortindices(void)
{
std::sort(I.begin(), I.end(), lessthan(*this));
}
};
int main()
{
example x;
x.displaydata();
x.sortindices();
x.displaydata();
return 0;
}
I am trying to map reserved memory (30M with offset of 2G) at boot time (boot kernel parameters mem=2G memmap=30M$2G) to user space using the remap_pfn_range, bellow is my driver code:
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <asm/uaccess.h>
// #include <asm/error.h>
#define MAP_MAJOR 150
#define RAW_DATA_SIZE 0x1E00000 // 30 Mo
#define RAW_DATA_OFFSET 0x80000000 //2G
int results;
static void *rawdataStart = NULL;
static int map_mmap(struct file *filp, struct vm_area_struct *vma);
struct file_operations map_fops = {
.open = nonseekable_open,
.mmap = map_mmap
};
static int map_mmap(struct file *filp, struct vm_area_struct *vma) {
if (rawdataStart == NULL) {
printk(KERN_ERR "Memory not mapped!\n");
return -EAGAIN;
}
if ((vma->vm_end - vma->vm_start) != RAW_DATA_SIZE) {
printk(KERN_ERR "Error: sizes don't match (buffer size = %d, requested size = %lu)\n", RAW_DATA_SIZE, vma->vm_end - vma->vm_start);
return -EAGAIN;
}
results = remap_pfn_range(vma, vma->vm_start, RAW_DATA_OFFSET >> PAGE_SHIFT, RAW_DATA_SIZE, PAGE_SHARED);
if (results != 0) {
printk(KERN_ERR "Error in calling remap_pfn_range: returned %d\n", results);
return -EAGAIN;
}
return 0;
}
static int __init map_init(void)
{
printk("init map module\n");
if (register_chrdev(MAP_MAJOR,"mapReserved", &map_fops) <0 )
{
printk("unable to get major for map module\n");
return -EBUSY;
}
rawdataStart = ioremap(RAW_DATA_OFFSET, RAW_DATA_SIZE);
if (rawdataStart == NULL) {
printk(KERN_ERR "Unable to remap memory\n");
return 1;
}
printk(KERN_INFO "ioremap returned %p\n", rawdataStart);
return 0;
}
void __exit map_cleanup(void)
{
printk("exit map module\n");
unregister_chrdev(MAP_MAJOR,"mapReserved");
if (rawdataStart != NULL) {
printk(KERN_INFO "Unmapping memory at %p\n", rawdataStart);
iounmap(rawdataStart);
} else {
printk(KERN_WARNING "No memory to unmap!\n");
}
return;
}
MODULE_LICENSE("GPL");
module_init( map_init);
module_exit( map_cleanup);
and my user space app is below
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#define RAW_DATA_SIZE 0x1E00000
int main(void)
{
void * data;
int fd = open("/dev/mapReserved", O_RDWR);
if (fd == -1) {
perror("open error...\n");
return -1;
}
data = mmap(NULL, RAW_DATA_SIZE, PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, fd, 4096);
close(fd);
return 0;
}
when i insert the module it's return
[ 873.621763] init map module
[ 873.623175] ioremap returned fb580000
but when i am executing the user space app it's return error
open error...
I've resolved this problem following those references :
1- Reserve memory in Linux driver module and share it using driver mmap
2- mmap of several GB of reserved memory using
in my case i am reserving 30M from the offset 2G and bellow is the code
module:
// #include <linux/config.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/debugfs.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/mm.h>
#include <linux/kdev_t.h>
#include <asm/page.h>
#include <linux/cdev.h>
#include <linux/device.h>
#ifndef VM_RESERVED
# define VM_RESERVED (VM_DONTEXPAND | VM_DONTDUMP)
#endif
#define RAW_DATA_SIZE 31457280
#define RAW_DATA_OFFSET 0x80000000UL
void *rawdataStart;
struct dentry *file;
/*
* Open the device; in fact, there's nothing to do here.
*/
int simple_open (struct inode *inode, struct file *filp)
{
return 0;
}
/*
* Closing is just as simpler.
*/
static int simple_release(struct inode *inode, struct file *filp)
{
return 0;
}
static int simple_remap_mmap(struct file *filp, struct vm_area_struct *vma)
{
int ret;
unsigned long mapoffset;
mapoffset = RAW_DATA_OFFSET + (vma->vm_pgoff << PAGE_SHIFT);
ret = remap_pfn_range(vma, vma->vm_start, mapoffset >> PAGE_SHIFT,
vma->vm_end - vma->vm_start, PAGE_SHARED);
if ( ret != 0 ) {
printk("Error remap_pfn_range. \n");
return -EAGAIN;
}
return 0;
}
/* Device uses remap_pfn_range */
static struct file_operations simple_remap_ops = {
.owner = THIS_MODULE,
.open = simple_open,
.release = simple_release,
.mmap = simple_remap_mmap,
};
/*
* Module housekeeping.
*/
static int simple_init(void)
{
file = debugfs_create_file("mmap_example", 0644, NULL, NULL, &simple_remap_ops);
rawdataStart = ioremap(RAW_DATA_OFFSET, RAW_DATA_SIZE);
if (rawdataStart!=NULL){
printk("rawdataStart at:%p \n", rawdataStart);
memset(rawdataStart, 'c', 20971520);
memset(rawdataStart+20971520, '$', 100);
}else{
printk("rawdataStart is NULL \n");
return -1;
}
return 0;
}
static void simple_cleanup(void)
{
debugfs_remove(file);
if (rawdataStart != NULL) {
printk(KERN_INFO "Unmapping memory at %p\n", rawdataStart);
iounmap(rawdataStart);
} else {
printk(KERN_WARNING "No memory to unmap!\n");
}
}
module_init(simple_init);
module_exit(simple_cleanup);
MODULE_AUTHOR("Jonathan Corbet");
MODULE_LICENSE("Dual BSD/GPL");
and the user space App:
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
#define RAW_DATA_SIZE 31457280
int main(int argc, char **argv) {
int configfd;
char * address = NULL;
unsigned long chkSum;
FILE *fp = fopen("results.log", "w+");
configfd = open("/sys/kernel/debug/mmap_example", O_RDWR);
if (configfd < 0) {
perror("Open call failed");
return -1;
}
address = (unsigned char*) mmap(NULL, RAW_DATA_SIZE, PROT_WRITE,
MAP_PRIVATE, configfd, 0);
if (address == MAP_FAILED) {
perror("mmap operation failed");
return -1;
}
fputs(address, fp);
fclose(fp);
close(configfd);
return 0;
}
All I do is construct a BNode object. The debugger says that the constructor is causing a segmentation fault. Does anyone know what the problem is here?
All I do is construct a BNode object. The debugger says that the constructor is causing a segmentation fault. Does anyone know what the problem is here?
#ifndef BTree_H
#define BTree_H
#include <iostream>
#include <fstream>
#include <cctype>
#include <string>
#include <sstream>
#include <cmath>
using namespace std;
template <typename T>
class BNode
{
public:
BNode();
BNode(int M);
~BNode();
int keyCount;
BNode *pointers;
T *keys;
};
template<typename T>
BNode<T>::BNode()
{
}
template<typename T>
BNode<T>::BNode(int M)
{
pointers = new BNode<T>[M];
keys = new T[M - 1];
}
template<typename T>
BNode<T>::~BNode()
{
delete[] pointers;
delete[] keys;
}
#endif
int main()
{
BNode<int> obj(5);
return 0;
}
You are deleting an array of pointers and keys, whereas you never defined these to be arrays.
Both of these are pointers.
You need to be freeing memory from the pointers, not arrays.
Try this:-
delete myPointer;
myPointer = NULL;
NOTE: If you're using C++, read about smart pointers. They'll come in handy!
A smart pointer clears the memory if the pointer gets out of scope. I wanted to adapt this to a file descriptor, like a socket. There you need a user defined deleter, because close() is the function to free the file descriptor (fd) resources.
I found this useful page, unfortunately, most approaches did not work for me. Below is a working solution I found up to now, which is a little nasty. Because uniqu_ptr expects a pointer I created int *fd to store the fd value, therefore, I had to close(*fd) and delete fd in my custom deleter.
(1) Is there a better way?
Options A and B, which are based on the hints provided by the mentioned web page, are much nicer but causing odd compiler errors.
(2) Does anyone know how to correctly use these alternatives?
I'm using Qt Creator 3.0.1 with CONFIG += c++11 option and gcc version 4.8.2
#include "ccommhandler.h"
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <memory>
#include <qdebug.h>
//for Option A and B
struct CloseHandleDeleter {
typedef int pointer;
void operator()(int handle) const
{
}
};
//custom deleter, working
class MyComplexDeleter
{
public:
MyComplexDeleter() {}
void operator()(int* ptr) const
{
qDebug() << "Deleting ";
close(*ptr);
delete ptr;
}
};
CCommHandler::CCommHandler()
{
//Option A doesn't work
//std::unique_ptr<int, CloseHandleDeleter> file( socket(AF_INET, SOCK_STREAM, 0) );
//Option B doesn't work
//std::unique_ptr<int, int()(int)> filePtr( socket(AF_INET, SOCK_STREAM, 0) , close);
MyComplexDeleter deleter;
int *fd = new int;
*fd = socket(AF_INET, SOCK_STREAM, 0);
std::unique_ptr<int, MyComplexDeleter> p( fd , deleter);
}
Edit:
The posted answer by Nevin is right, it solves my initial problem.
The comment of learnvst caused to rethink my problem, and I have to say I may made it much more complex than needed, because the following simple class should also solve my problem of auto-free the memory of a resource or as in my case, to close the file descriptor:
class SocketHandler
{
int _fd;
public:
SocketHandler(int FD):_fd(FD){}
~SocketHandler() { if(_fd!=-1) close(_fd); }
operator int() const { return _fd; }
};
Because fd isn't a pointer, I wouldn't try to pigeonhole it into unique_ptr. Instead, create a custom class whose interface is based on unique_ptr, as in (caution: totally untested):
class unique_fd
{
public:
constexpr unique_fd() noexcept = default;
explicit unique_fd(int fd) noexcept : fd_(fd) {}
unique_fd(unique_fd&& u) noexcept : fd_(u.fd_) { u.fd_ = -1; }
~unique_fd() { if (-1 != fd_) ::close(fd_); }
unique_fd& operator=(unique_fd&& u) noexcept { reset(u.release()); return *this; }
int get() const noexcept { return fd_; }
operator int() const noexcept { return fd_; }
int release() noexcept { int fd = fd_; fd_ = -1; return fd; }
void reset(int fd = -1) noexcept { unique_fd(fd).swap(*this); }
void swap(unique_fd& u) noexcept { std::swap(fd_, u.fd_); }
unique_fd(const unique_fd&) = delete;
unique_fd& operator=(const unique_fd&) = delete;
// in the global namespace to override ::close(int)
friend int close(unique_fd& u) noexcept { int closed = ::close(u.fd_); u.fd_ = -1; return closed; }
private:
int fd_ = -1;
};