[英]Why does this C++0x program generates unexpected output?
該程序:
#include <boost/signal.hpp>
#include <utility>
class Sensor;
class Recorder : public ::boost::signals::trackable {
public:
explicit Recorder(int id) : id_(id) {}
// Cannot be copied
Recorder(const Recorder &) = delete;
Recorder &operator =(const Recorder &) = delete;
// But can be moved so it can be stored in a vector.
// There's a proposal for having a compiler generated default for this that would be
// very convenient.
Recorder(Recorder &&b) : id_(b.id_) {
b.id_ = -1;
}
Recorder &operator =(Recorder &&b) {
id_ = b.id_;
b.id_ = -1;
return *this;
}
void recordSensor(const Sensor &s);
void addSensor(Sensor &s);
private:
int id_;
char space_[1312];
};
class Sensor {
public:
typedef ::boost::signal<void (const Sensor &)> sigtype_t;
explicit Sensor(int id) : val_(0), id_(id) { }
void notify(const sigtype_t::slot_type &slot) { signal_.connect(slot); }
void updateSensor(double newval) { val_ = newval; signal_(*this); }
double getValue() const { return val_; }
int getId() const { return id_; }
private:
sigtype_t signal_;
double val_;
const int id_;
};
#include "test_header.hpp"
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
void Recorder::addSensor(Sensor &s)
{
::std::cout << "Recorder #" << id_
<< " now recording Sensor #" << s.getId() << '\n';
::std::cout.flush();
s.notify(::boost::bind(&Recorder::recordSensor, this, _1));
}
void Recorder::recordSensor(const Sensor &s)
{
::std::cout << "Recorder #" << id_ << " - new value for sensor named Sensor #"
<< s.getId() << ": " << s.getValue() << '\n';
::std::cout.flush();
}
int main(int argc, const char *argv[])
{
using ::boost::shared_ptr;
using ::std::vector;
vector<Recorder> recorders;
vector<shared_ptr<Sensor> > sensors;
double val = 0.1;
static const unsigned int recorder_every = 4;
static const unsigned int sensor_every = 2;
for (unsigned int i = 0; i < 9; ++i) {
if (i % recorder_every == 0) {
recorders.push_back(Recorder(i / recorder_every));
}
if (i % sensor_every == 0) {
shared_ptr<Sensor> sp(new Sensor(i / sensor_every));
sensors.push_back(sp);
for (auto r = recorders.begin(); r != recorders.end(); ++r) {
r->addSensor(*sp);
}
}
for (auto s = sensors.begin(); s != sensors.end(); ++s, val *= 1.001) {
(*s)->updateSensor(val);
}
}
}
我得到以下輸出:
Recorder #0 now recording Sensor #0
Recorder #0 - new value for sensor named Sensor #0: 0.1
Recorder #0 - new value for sensor named Sensor #0: 0.1001
Recorder #0 now recording Sensor #1
Recorder #0 - new value for sensor named Sensor #0: 0.1002
Recorder #0 - new value for sensor named Sensor #1: 0.1003
Recorder #0 - new value for sensor named Sensor #0: 0.100401
Recorder #0 - new value for sensor named Sensor #1: 0.100501
Recorder #0 now recording Sensor #2
Recorder #1 now recording Sensor #2
Recorder #0 - new value for sensor named Sensor #2: 0.100803
Recorder #1 - new value for sensor named Sensor #2: 0.100803
Recorder #0 - new value for sensor named Sensor #2: 0.101106
Recorder #1 - new value for sensor named Sensor #2: 0.101106
Recorder #0 now recording Sensor #3
Recorder #1 now recording Sensor #3
Recorder #0 - new value for sensor named Sensor #2: 0.101409
Recorder #1 - new value for sensor named Sensor #2: 0.101409
Recorder #0 - new value for sensor named Sensor #3: 0.101511
Recorder #1 - new value for sensor named Sensor #3: 0.101511
Recorder #0 - new value for sensor named Sensor #2: 0.101815
Recorder #1 - new value for sensor named Sensor #2: 0.101815
Recorder #0 - new value for sensor named Sensor #3: 0.101917
Recorder #1 - new value for sensor named Sensor #3: 0.101917
Recorder #0 now recording Sensor #4
Recorder #1 now recording Sensor #4
Recorder #2 now recording Sensor #4
Recorder #0 - new value for sensor named Sensor #4: 0.102428
Recorder #1 - new value for sensor named Sensor #4: 0.102428
Recorder #2 - new value for sensor named Sensor #4: 0.102428
我有點困惑。 當我添加一個記錄器時,似乎所有舊的傳感器都被遺忘了。
記錄器可以在內存中移動,因為您在創建矢量時會添加它們,但是在執行此操作時會綁定到它們以發出信號。
給記錄器一個指向傳感器矢量的索引,而不是指向該傳感器的指針。 只要您不刪除傳感器,就可以正常工作。
Ergosys已經描述了問題的原因。 解決方案缺少的是:在綁定信號之前,請確保已完成將所有記錄器和傳感器添加到矢量中。 這樣,他們的地址將完成更改。
這是主循環的修訂版:
for (unsigned int i = 0; i < 9; ++i) {
if (i % recorder_every == 0) {
recorders.push_back(Recorder(i / recorder_every));
}
if (i % sensor_every == 0) {
shared_ptr<Sensor> sp(new Sensor(i / sensor_every));
sensors.push_back(sp);
}
}
for (unsigned int i = 0; i < 9; ++i) {
if (i % sensor_every == 0) {
for (auto r = recorders.begin(); r != recorders.end(); ++r) {
shared_ptr<Sensor> sp = sensors[i / sensor_every];
r->addSensor(*sp);
}
}
for (auto s = sensors.begin(); s != sensors.end(); ++s, val *= 1.001) {
(*s)->updateSensor(val);
}
}
您是否嘗試過使用直數組而不是:: std :: vector? 我知道:: std :: vector是一種時尚的東西,但它實際上不是向量(更像是一個半列表半數組)。
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