I'm using something like the following. Is there a better way?
for (int i = 0; i < sizeof(Person) ; i++) {
const char &cr = *((char*)personPtr + i);
cout << bitset<CHAR_BIT>(cr);
}
I would suggest to provide a serialize_as_binary utility in your Person class.
template<typename T>
void serialize_as_bin(const T &t, ostream& os) {
const unsigned char *p = reinterpret_cast<const unsigned char *>(&t);
for(size_t s = 0; s < sizeof t; ++s, ++p) serialize_as_bin(*p, os);
}
template<>
void serialize_as_bin(const unsigned char &t, ostream& os) {
// Code to serialize one byte
std::bitset<CHAR_BIT> x(t);
os << x;
}
struct Person {
A a;
B b;
ostream& serialize_as_binary(ostream& os) {
serialize_as_bin(a, os);
serialize_as_bin(b, os);
return os;
}
void deserialize_from_binary() {
// Similar stuff if required
...
}
};
Live example here
Disclaimer: This is meant as a simple non-serious solution that doesn't care about padding. Prints the bytes and bits from right to left.
template<typename T>
void PrintBits(const T& o) {
for (size_t i = sizeof(o) - 1; i < sizeof(o); --i)
std::cout << std::bitset<CHAR_BIT>(reinterpret_cast<const unsigned char*>(&o)[i]);
}
Related
I'm storing my class object in the binary file but I'm getting weird results when I load the data.
Following Code is Loading and Saving Data:
#include <iostream>
#include <fstream>
#include <memory>
#include <string>
#include <sstream>
using namespace std;
template <class C>
void Load(const char fileName[], C& obj)
{
ifstream in;
in.open(fileName, ios::in | ios::binary);
in.read(reinterpret_cast<char*>(addressof(obj)), sizeof(obj));
in.close();
return;
}
template <class T>
void Save(const char fileName[], T obj)
{
ofstream out;
out.open(fileName, ios::out | ios::binary);
out.write(reinterpret_cast<char const*>(addressof(obj)), sizeof(obj));
stringstream ss;
out.close();
return;
}
class Contact {
public:
int CompareTo(Contact obj)
{
return 1;
}
string ss;
int rollNum;
};
class Data {
public:
Data()
{
}
Contact arr[10];
};
int main()
{
const char fileName[] = "ContactMG.dat";
/*
Data *T = new Data();
for(int i=0;i<10;i++)
T->arr[i].ss = "fahad";
Save(fileName , *T);
*/
Data* d = new Data();
Load(fileName, *d);
for (int i = 0; i < 10; i++)
cout << d->arr[i].ss << endl;
}
/*
Console outPut:
ⁿx
p²x
σß╥Z∙
░▒▓│┤
>
☺Y╩
░‼╩
*/
/* Binary File
#® ® ®
*/
I want to ask how I can store this object in the binary file and load it?
I'm pretty sure the problem is with string but I don't know how to fix it!
I have already known to store strings in binary files but don't know how to store class objects which have string in it
I would introduce a new level of indirection, i.e. functions from_binary and to_binary, and implement your Load and Store in terms of those:
template <class C>
bool Load(const char fileName[], C& obj) {
if (ifstream in{fileName, ios::in | ios::binary}) {
from_binary(in, obj);
return true;
}
return false;
}
template <class T>
bool Save(const char fileName[], T obj) {
if (ofstream out{fileName, ios::out | ios::binary}) {
to_binary(out, obj);
return true;
}
return false;
}
For POD data types, from_binary and to_binary will just do what you already did in Load/Store (beware, however: pointers are PODs but saving an address is pretty much meaningless):
template <class T, typename = enable_if_t<is_pod_v<T>>>
void from_binary(ifstream& in, T& obj) {
in.read(reinterpret_cast<char*>(addressof(obj)), sizeof(obj));
}
template <class T, typename = enable_if_t<is_pod_v<T>>>
void to_binary(ofstream& out, T const& obj) {
out.write(reinterpret_cast<char const*>(addressof(obj)), sizeof(obj));
}
As pointed out in the comments, std::string is not a POD type. I'm going to serialize it by saving the character count and then the actual characters:
void from_binary(ifstream& in, string& str) {
std::size_t stringSize{0};
from_binary(in, stringSize);
str.reserve(stringSize);
for (size_t i = 0; i != stringSize; ++i) {
char ch{};
in.read(&ch, 1);
str.push_back(ch);
}
}
void to_binary(ofstream& out, string const& str) {
auto const stringSize = str.size();
to_binary(out, stringSize);
auto const* cStr = str.c_str();
out.write(cStr, stringSize);
}
Also, I'm going to serialize/deserialize an array by calling to_binary/from_binary on each element of the array:
template <class T, size_t N>
void from_binary(ifstream& in, T (&obj)[N]) {
for (auto& elem : obj) from_binary(in, elem);
}
template <class T, size_t N>
void to_binary(ofstream& out, T const (&obj)[N]) {
for (auto const& elem : obj) to_binary(out, elem);
}
The above functions are enough to implement from_binary and to_binary for your Contact and Data classes:
#include <fstream>
#include <iostream>
#include <string>
using namespace std;
template <class T, typename = enable_if_t<is_pod_v<T>>>
void from_binary(ifstream& in, T& obj) {
in.read(reinterpret_cast<char*>(addressof(obj)), sizeof(obj));
}
template <class T, typename = enable_if_t<is_pod_v<T>>>
void to_binary(ofstream& out, T const& obj) {
out.write(reinterpret_cast<char const*>(addressof(obj)), sizeof(obj));
}
void from_binary(ifstream& in, string& str) {
std::size_t stringSize{0};
from_binary(in, stringSize);
str.reserve(stringSize);
for (size_t i = 0; i != stringSize; ++i) {
char ch{};
in.read(&ch, 1);
str.push_back(ch);
}
}
void to_binary(ofstream& out, string const& str) {
auto const stringSize = str.size();
to_binary(out, stringSize);
auto const* cStr = str.c_str();
out.write(cStr, stringSize);
}
template <class T, size_t N>
void from_binary(ifstream& in, T (&obj)[N]) {
for (auto& elem : obj) from_binary(in, elem);
}
template <class T, size_t N>
void to_binary(ofstream& out, T const (&obj)[N]) {
for (auto const& elem : obj) to_binary(out, elem);
}
template <class C>
bool Load(const char fileName[], C& obj) {
if (ifstream in{fileName, ios::in | ios::binary}) {
from_binary(in, obj);
return true;
}
return false;
}
template <class T>
bool Save(const char fileName[], T obj) {
if (ofstream out{fileName, ios::out | ios::binary}) {
to_binary(out, obj);
return true;
}
return false;
}
class Contact {
public:
int CompareTo(Contact obj) { return 1; }
string ss;
int rollNum;
};
void from_binary(ifstream& in, Contact& obj) {
from_binary(in, obj.ss);
from_binary(in, obj.rollNum);
}
void to_binary(ofstream& out, Contact const& obj) {
to_binary(out, obj.ss);
to_binary(out, obj.rollNum);
}
class Data {
public:
Data() {}
Contact arr[10];
};
void from_binary(ifstream& in, Data& obj) { from_binary(in, obj.arr); }
void to_binary(ofstream& out, Data const& obj) { to_binary(out, obj.arr); }
int main() {
const char fileName[] = "ContactMG.dat";
{
Data data;
auto const contactCount = sizeof(data.arr) / sizeof(data.arr[0]);
for (size_t c = 0; c != contactCount; ++c) {
data.arr[c].ss = "some name " + to_string(c);
data.arr[c].rollNum = c;
}
Save(fileName, data);
}
{
Data data;
Load(fileName, data);
for (auto const& contact : data.arr)
cout << "Contact: rollNum=" << contact.rollNum
<< ", ss=" << contact.ss << '\n';
}
}
Output:
Contact: rollNum=0, ss=some name 0
Contact: rollNum=1, ss=some name 1
Contact: rollNum=2, ss=some name 2
Contact: rollNum=3, ss=some name 3
Contact: rollNum=4, ss=some name 4
Contact: rollNum=5, ss=some name 5
Contact: rollNum=6, ss=some name 6
Contact: rollNum=7, ss=some name 7
Contact: rollNum=8, ss=some name 8
Contact: rollNum=9, ss=some name 9
Although this may solve your particular issue, the number of overloads you'll need for from_binary and to_binary will grow very rapidly as your project grows. So I'd definetely check if there's a more comprehensive (and well tested) library solution out there.
In the code bellow, instead of using new function "void print()", how can I use the overloaded "<<" operator in order to print the required information?
Or to be exact, where is the mistake here?
Overloaded << operator in one of the inherited classes:
friend ostream &operator<<(ostream &os, DigitSecret &s){
for(int i=0;i<s.n;i++)
os<<s.digits[i];
return os<<" Simple entropy: "<<s.simpleEntropy()<<" Total: "<<s.total();
}
void printAll (Secret ** secrets, int n) {
for(int i=0;i<n;i++){
cout<<secret[i] //This is printing an address, however that is not what i want.
secrets[i]->print(); //I want that to work like this.
}
}
The whole code: https://pastebin.com/MDCsqUxJ
I want line 134 and 143 to work correctly.
EDIT:
secret[i] is of type Secret*, you should derefence first and then your overload will get picked:
cout << *secret[i];
Side note: use std::vector instead of raw dynamic allocation.
See this snippet:
class base {
public:
virtual void print() = 0;
virtual std::ostringstream get_value() const = 0;
int get_id() const { return id_; }
protected:
int id_;
};
class A:public base {
public:
A(std::string val):val_(val){ id_ = 1; }
void print() override { std::cout << " I am A" << std::endl; }
std::ostringstream get_value() const { std::ostringstream ss; ss << val_; return ss; }
private:
std::string val_;
};
class B :public base {
public:
B(int val):val_(val) { id_ = 2; }
void print() override { std::cout << " I am B" << std::endl; }
virtual std::ostringstream get_value() const { std::ostringstream ss; ss << val_; return ss; }
private:
int val_;
};
std::ostream& operator << (std::ostream& os, const base* p)
{
std::string str;
if (p->get_id() == 1) {
str = ((A*)(p))->get_value().str();
os << "A " << str << "\n";
}
else
if (p->get_id() == 2) {
str = ((B*)(p))->get_value().str();
os << "B " << str << "\n";
}
return os;
}
void PrintAll(base** a)
{
for (int i = 0; i<2; i++)
std::cout << a[i];
}
int main()
{
base* a[2];
a[0] = new A("Hello");
a[1] = new B(10);
PrintAll(a);
return 0;
}
Output:
I Solved it this way:
void printAll (Secret ** secrets, int n) {
for(int i=0;i<n;i++){
DigitSecret* ds = NULL;
CharSecret* cs = NULL;
ds = dynamic_cast<DigitSecret*>(secrets[i]);
cs = dynamic_cast<CharSecret*>(secrets[i]);
if(ds!=NULL)
cout<<*ds<<endl;
else
cout<<*cs<<endl;
// secrets[i]->print();
}
}
Basically in this case, I have to use dynamic_cast with new pointer from the derived class, on each pointer from the array, and check if the pointer is !=NULL, and then use the overloaded operator on the dereferenced new pointer.
Say I have a simple vector class, vec:
#include <iostream>
#include <stdlib.h>
class vec {
public:
vec() {}
// Constructor.
vec(int n) {
len = n;
data = new double[len];
}
// Destructor.
~vec() { delete [] data; }
// Accessor.
double & operator[](int i) const {
check_index(i);
return data[i];
}
// Other methods...
// ....
protected:
int len;
double * data;
void check_index(int i) const {
if(i < 0 || i >= len) {
std::cerr << "Bad access.\n";
exit(1);
}
}
};
Now suppose I have a special type of vector with sparse structure, e.g., where every even-index is zero. Call this oddvec. Instances of oddvec should be declared just as with the vec class, but underneath, the memory use should be efficient since only half the data is non-zero.
The accessor for the oddvec class should return 0 if the index is even, and return the odd-index element (stored sequentially) otherwise. There a couple problems with this:
The double & return type is violated if the index is even, since the constant value, 0, is returned.
It's not clear to me how to handle the situation when an even index element is used as an lvalue. E.g., v[0] = 3.0 should not be allowed in the oddvec class, but is perfectly acceptable in the vector class. We can't simply throw an error when even indexes are used, because even indexes are fine as long as the intention is as an rvalue.
How do I design the accessor function for the oddvec class, while both keeping the memory storage efficient and inheriting all the methods from the parent?
Non-working example of oddvec:
class oddvec : public vec {
public:
// Constructor.
oddvec(int n) {
len = n;
data = new double[len/2];
}
// Accessor (doesn't work!)
double & operator[](int i) const {
check_index(i);
if (i%2 == 0)
return 0;
else
return data[(i-1)/2];
}
};
Upon compilation:
main.cpp: In member function ‘double& oddvec::operator[](int) const’:
main.cpp:49:20: error: invalid initialization of non-const reference of type ‘double&’ from an rvalue of type ‘double’
return 0;
Working example using proxy classes:
I have implemented a proxy class as suggested in the answer below.
proxies.h
#ifndef PROXIES_H
#define PROXIES_H
#include <iostream>
#include <stdlib.h>
class proxy {
public:
proxy(int i, double v, double * d) {
index = i;
value = v;
data = d;
}
void operator=(double rhs) {
data[index] = rhs;
}
friend std::ostream & operator<<(std::ostream & outs, const proxy & p) {
outs << p.value;
return outs;
}
protected:
int index;
double value;
double * data;
};
class oddproxy : public proxy {
public:
oddproxy(int i, int v, double * d) : proxy(i, v, d) {}
void operator=(double rhs) {
if (index%2 == 0) {
std::cerr << "Even entries of oddvec are not assignable.\n";
exit(1);
}
data[index/2] = rhs;
}
};
#endif
vectors.h
#ifndef VECTORS_H
#define VECTORS_H
#include "proxies.h"
class vec {
public:
vec() {}
// Constructor.
vec(int n) {
len = n;
data = new double[len];
}
// Destructor.
~vec() { delete [] data; }
// Accessor.
proxy operator[](int i) const {
check_index(i);
return proxy(i, data[i], data);
}
inline int length() const { return len; }
// Other methods...
// ....
protected:
int len;
double * data;
void check_index(int i) const {
if(i < 0 || i >= len) {
std::cerr << "Bad access.\n";
exit(1);
}
}
};
class oddvec : public vec {
public:
// Constructor.
oddvec(int n) {
len = n;
data = new double[len/2];
}
// Accessor.
oddproxy operator[](int i) const {
check_index(i);
return oddproxy(i, (i%2 == 0) ? 0 : data[i/2], data);
}
};
#endif
main.cpp
#include <iostream>
#include "vectors.h"
int main () {
int N = 5;
vec V(N);
oddvec O(N);
for(int i=0; i < V.length(); i++) {
V[i] = i;
if(i%2 != 0) {
O[i] = i;
}
}
for(int i=0; i < O.length(); i++) {
std::cout << "V[" << i << "]=" << V[i] << ", "
<< "O[" << i << "]=" << O[i] << "\n";
}
O[0] = 13;
return 0;
}
output
V[0]=0, O[0]=0
V[1]=1, O[1]=1
V[2]=2, O[2]=0
V[3]=3, O[3]=3
V[4]=4, O[4]=0
Even entries of oddvec are not assignable.
You can use proxy object to do this.
simple sample code:
#include <iostream>
#include <vector>
using namespace std;
class very_odd_vector{
public:
class only_odd_proxy;
friend class only_odd_proxy;
only_odd_proxy operator [](int index);
int operator [](int index)const{return index%2==0?0:content[index/2];}
unsigned int size()const{return content.size()*2;}
private:
vector<int> content{1,3,5,7,9};
};
class very_odd_vector::only_odd_proxy{
public:
only_odd_proxy(very_odd_vector& vec,int index):vec(vec),index(index){}
operator int(){return index%2==0 ? 0 : vec.content[index/2];}
only_odd_proxy& operator =(int value){
if(index%2==0)
cout << "BAD OPERATION";//any error you want
else
vec.content[index/2] = value;
return *this;
}
private:
very_odd_vector& vec;
int index;
};
auto very_odd_vector::operator [](int index)->only_odd_proxy{return only_odd_proxy(*this,index);}
int main(){
very_odd_vector v;
cout << "reading value\n";
for(int i=0;i<v.size();++i)
cout << v[i] <<'\n';
cout << "writting value\n";
for(int i=0;i<v.size();++i){
cout << i << ':';
v[i]=10;
cout << '\n';
}
cout << "reading value\n";
for(int i=0;i<v.size();++i)
cout << v[i] <<'\n';
}
Edit for updated part of question :
I think this class will fit your need more.
//Both base and inherit class return this class
class maybe_readonly_proxy {
public:
maybe_readonly_proxy(double* data, bool readonly):readonly(readonly),data(data){}
maybe_readonly_proxy& operator=(double rhs) {
if(readonly){/*whatever error*/}
else {*data = rhs;}
return *this;
}
operator double()const{return *data;}
private:
bool readonly;
double * data;
};
You may need a variable to contain readonly (0 in this case) value, or modify the operator double() the check readonly state
Or just implement get and set method separately and do not use this proxy may be another choice.
I'm working on a simple progress indicator class, and I have a question about using a std::ostream object as a class member. The following example compiles and runs correctly on OS X and Linux.
#include <iostream>
#include <string>
struct ProgressIndicator {
public:
ProgressIndicator(unsigned int update_interval, std::string message,
std::ostream& outstream = std::cerr)
: update_interval(update_interval), message(message),
stream(outstream.rdbuf()), _counter(0), _interval(update_interval)
{
}
void increment(unsigned int by = 1)
{
_counter += by;
if(_counter >= _interval) {
stream << message << _counter << std::endl;
_interval += update_interval;
}
}
unsigned int get_count()
{
return _counter;
}
protected:
unsigned int update_interval;
std::string message;
std::ostream stream;
private:
unsigned long _counter;
unsigned long _interval;
};
int main()
{
ProgressIndicator p1(5, "progress <stdout> ", std::cout);
for(int i = 0; i < 15; i++) {
p1.increment();
}
ProgressIndicator p2(5, "progress <stderr> ", std::cerr);
for(int i = 0; i < 15; i++) {
p2.increment();
}
return 0;
}
I understand that std::ostream objects cannot be copied, and must be passed by reference. But I don't understand why initializing with stream(outstream) doesn't work, and why I had to resort to the rdbuf() hack. Is there no "better", more idiomatic way to do this?
You are still copying the std::ostream. Even though the constructor isn't copying the parameter, it still needs to copy the object into ProgressIndicator::stream somehow.
One way to solve your problem would be to store a reference to the stream, though this only works if you know the stream object will outlast your class instance:
struct ProgressIndicator {
ProgressIndicator(std::ostream& outstream = std::cerr /* ... */)
: stream(outstream) /* ... */ {}
// ...
protected:
std::ostream& stream;
// ...
};
I have some trouble with class template inheritance and operators (operator +),
please have a look at these lines:
Base vector class (TVector.h):
template<class Real, int Size>
class TVector {
protected:
Real* values;
public:
...
virtual TVector<Real, Size>& operator=(const TVector<Real, Size>& rTVector) { //WORKS
int i = 0;
while (i<Size) {
*(values+i) = *(rTVector.values+i);
i++;
}
return *this;
}
virtual TVector<Real, Size> operator+(const TVector<Real, Size>& rTVector) const {
int i = 0;
Real* mem = (Real*)malloc(sizeof(Real)*Size);
memcpy(mem, values, Size);
while (i<Size) {
*(mem+i) += *(rTVector.values+i);
i++;
}
TVector<Real, Size> result = TVector<Real, Size>(mem);
free(mem);
return result;
}
};
2D vector class (TVector2.h):
template<class Real>
class TVector2: public TVector<Real, 2> {
public:
...
TVector2& operator=(const TVector2<Real>& rTVector) { //WORKS
return (TVector2&)(TVector<Real, 2>::operator=(rTVector));
}
TVector2 operator+(TVector2<Real>& rTVector) const { //ERROR
return (TVector2<Real>)(TVector<Real, 2>::operator+(rTVector));
}
};
Test (main.cpp):
int main(int argc, char** argv) {
TVector2<int> v = TVector2<int>();
v[0]=0;
v[1]=1;
TVector2<int> v1 = TVector2<int>();
v1.X() = 10;
v1.Y() = 15;
v = v + v1; //ERROR ON + OPERATOR
return 0;
}
Compilation error (VS2010):
Error 2 error C2440: 'cast de type' : cannot convert from
'TVector<Real,Size>' to 'TVector2' ...
What is wrong here ? is there a way to do this kind of stuff ?
Just looking for a way to not redefine all my Vectors classes.
I keep searching to do it, but I will be glad to get some help from you guys.
Sorry for bad English,
Best regards.
#include <memory>
using namespace std;
template<class Real, int Size> class TVector {
protected:
Real *_values;
public:
TVector() {
// allocate buffer
_values = new Real[Size];
}
TVector(Real *prValues) {
// check first
if (prValues == 0)
throw std::exception("prValues is null");
// allocate buffer
_values = new Real[Size];
// initialize buffer with values
for (unsigned int i(0U) ; i < Size ; ++i)
_values[i] = prValues[i];
}
// Do not forget copy ctor
TVector(TVector<Real, Size> const &rTVector) {
// allocate buffer
_values = new Real[Size];
// initialize with other vector
*this = rTVector;
}
virtual ~TVector() {
delete [] _values;
}
virtual Real &operator[](int iIndex) {
// check for requested index
if (iIndex < 0 || iIndex >= Size)
throw std::exception("requested index is out of bounds");
// index is correct. Return value
return *(_values+iIndex);
}
virtual TVector<Real, Size> &operator=(TVector<Real, Size> const &rTVector) {
// just copying values
for (unsigned int i(0U) ; i < Size ; ++i)
_values[i] = rTVector._values[i];
return *this;
}
virtual TVector<Real, Size> &operator+=(TVector<Real, Size> const &rTVector) {
for (unsigned int i(0U) ; i < Size ; ++i)
_values[i] += rTVector._values[i];
return *this;
}
virtual TVector<Real, Size> operator+(TVector<Real, Size> const &rTVector) {
TVector<Real, Size> tempVector(this->_values);
tempVector += rTVector;
return tempVector;
}
};
template<class Real> class TVector2: public TVector<Real, 2> {
public:
TVector2() {};
TVector2(Real *prValues): TVector(prValues) {}
TVector2 &operator=(TVector2<Real> const &rTVector) {
return static_cast<TVector2 &>(TVector<Real, 2>::operator=(rTVector));
}
TVector2 &operator+=(TVector2<Real> const &rTVector) {
return static_cast<TVector2 &>(TVector<Real, 2>::operator+=(rTVector));
}
TVector2 operator+(TVector2<Real> const &rTVector) {
return static_cast<TVector2 &>(TVector<Real, 2>::operator+(rTVector));
}
Real &X() { return _values[0]; }
Real &Y() { return _values[1]; }
};
int main(int argc, char** argv) {
TVector2<int> v = TVector2<int>();
v[0]=0;
v[1]=1;
TVector2<int> v1 = TVector2<int>();
v1.X() = 10;
v1.Y() = 15;
v = v1;
v += v1;
v = v + v1;
return 0;
}
Some misc notes:
it's very bad that you use malloc against of new. Real can be POD only to allow vector work well in your case. Use new or provide custom creation policy if you think that malloc provides better performance on PODs. Also do not forget to use delete [] instead of free while destroying memory buffer.
It's better to perform bounds checking while overloading operator[]
for better performance use ++i instead of postfix form. In former no temporary value is created.