Not too many have answered my questions at all. What I want to do a to use private copy constructors and assign them to variables as string or binary files.
Here is the code.
#include "stdafx.h"
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
class President
{
private:
President() {};
President(const President&);
const President& operator=(const President&);
string Name;
public:
static President& GetInstance()
{
static President OnlyInstance;
return OnlyInstance;
}
string GetFile()
{
cout<<"Enter the name of the file you want to protect: ";
cin>>Name;
ofstream fsOut;
fsOut.open(Name, ios_base::out, ios_base::binary);
if(fsOut.is_open())
{
cout<<"Writing to binary file."<<endl;
fsOut<<Name<<endl;
cout<<"File open successful."<<endl;
fsOut.close();
}
return Name;
}
void SetFile(string InputFile)
{
Name=InputFile;
}
};
int main()
{
string Name;
President& OnlyPresident=President::GetInstance();
OnlyPresident.SetFile(Name);
cout<<President::GetInstance().GetFile()<<endl;
return 0;
}
I have compiled it and it was fine. However, it was not running correctly or it did not correspond to the file, in which I have typed. How could I protect files correctly using private copy constructors?
John P.
Related
This question already has answers here:
Can't access function from header file
(2 answers)
Closed 6 years ago.
I am learning C++. I am practising splitting my C++ class into separate files- implementation and header files namely Student_Impl.cpp and Student_Header.h. And then there is a driver file Student_register.cpp which will create 3 Student objects. However, when I try to build it, it's throwing errors stating Student is not a namespace or class. I have included the Student_Header.h (where Student class declaration is present) in my implementation file Student_Impl.cpp and driver file Student_register.cpp but it still throwing the same errors. What can be the possible cause ? I am using Visual Studio 2015.
Student_Header.h
#pragma once
#include <string>
using namespace std;
class Student {
private:
string fname;
string lname;
string address;
string city;
string phone;
int age;
public:
Student();
Student(string, string, string, string, string, int);
~Student();
string get_fname();
string get_lname();
string get_address();
string get_city();
string get_phone();
int get_age();
};
Student_Impl.cpp
#include "Student_Header.h"
#include "iostream"
#include "stdafx.h"
#include <string>
using namespace std;
Student::Student()
{
}
Student::Student(string fname1, string lname1, string address1, string city1, string phone1, int age1)
{
fname = fname1;
lname = lname1;
address = address1;
city = city1;
phone = phone1;
age = age1;
}
string Student::get_fname()
{
return fname;
}
string Student::get_lname()
{
return lname;
}
string Student::get_address()
{
return address;
}
string Student::get_city()
{
return city;
}
string Student::get_phone()
{
return phone;
}
int Student::get_age()
{
return age;
}
Student::~Student()
{}
Student_register.cpp
#include "stdafx.h"
#include "Student_Header.h"
#include <string>
#include "iostream"
using namespace std;
int main()
{
Student Student1("Mike", "J", "MikeAdd", "MikeCity", "MikePhone", 26);
Student Student2("Jack", "R", "JackAdd", "JackCity", "JackPhone", 25);
Student Student3("Roney", "M", "RoneyAdd", "RoneyCity", "RoneyPhone", 27);
// code for data retrieval
return 0;
}
Marvin Sielenkemper put the correct answer in the comment - headers prior to "stdafx.h" are ignored. This is an implementation-specific side effect of how precompiled headers work on Visual Studio.
Also, use #include <iostream> instead of #include "iostream". The <header> form is for standard headers, the "header.h" is for your own headers.
I'm creating a student data management console application for a project. I created a class called Student which is storing all the data that a student needs to have, and it also has all the getters and setters associated with it. Here is how all my files are laid out:
Student.h
#include <iostream>
#include <string>
using namespace std;
class Student {
private:
string name;
string id;
string email;
int presentation;
int essay1;
int essay2;
int project;
public:
//constructor
//Student();
//setters
void set_name(string);
void set_id(string);
void set_email(string);
void set_presentation(int);
void set_essay1(int);
void set_essay2(int);
void set_project(int);
//getters
string get_name();
string get_id();
string get_email();
int get_presentation();
int get_essay1();
int get_essay2();
int get_project();
};
Student.cpp
#include <iostream>
#include <string>
#include "Student.h"
using namespace std;
//constructor definition
/*
Student::Student(void) {
cout << "Student created" << endl;
}
*/
//setter definition
void Student::set_name(string s) {
name = s;
}
void Student::set_id(string s) {
id = s;
}
void Student::set_email(string s) {
email = s;
}
void Student::set_presentation(int a) {
presentation = a;
}
void Student::set_essay1(int a) {
essay1 = a;
}
void Student::set_essay2(int a) {
essay2 = a;
}
void Student::set_project(int a) {
project = a;
}
//getter definition
string Student::get_name() {
return name;
}
string Student::get_id() {
return id;
}
string Student::get_email() {
return email;
}
int Student::get_presentation() {
return presentation;
}
int Student::get_essay1() {
return essay1;
}
int Student::get_essay2() {
return essay2;
}
int Student::get_project() {
return project;
}
Main.cpp
#include <iostream>
#include <string>
#include "Student.h"
using namespace std;
int main() {
cout << "Hello World!" << endl;
Student student1;
Student student2;
Student student3;
student1.set_name("John");
student2.set_name("Bob");
student3.set_name("Carl");
return 0;
}
When I try to run my program, I get, amongst others, the following errors:
Error 1 error C2011: 'Student' : 'class' type redefinition
Error 2 error C2079: 'student1' uses undefined class 'Student'
Error 5 error C2228: left of '.set_name' must have class/struct/union
Error 9 error C2027: use of undefined type 'Student'
How can I go about fixing this issue?
I'm quite sure this is an error caused by the fact that student.h is included twice in a certain .cpp file. Thus you need to use so-called header guards to make sure the file is only included once in every .cpp file:
#ifndef STUDENT_H
#define STUDENT_H
#include <iostream>
#include <string>
using namespace std;
class Student {
/* ... */
};
#endif
The idea behind this is that an #include is a preprocessor directive that results in the argument file being copied into the file where the #include was issued. Hence, if files A and B include Student.h, and file C includes both files A and B, then the declaration of class Student is going to end up duplicated. Hence the error. The above macros make sure that this doesn't happen.
Edit as per the question author's comment:
#pragma once is the same as #ifndef .. #define #endif but non-standard .
See #pragma once vs include guards? for reference.
I had the same error. I just clean and rebuild the solution and error resolved.
can sombody explain to me why my code will not work, and how to fix it thanks :)
I keep recieving this error :
no 'int burrito::setName()' member function declared in class 'burrito'
My goal is to call a function from a different class file
My main.cpp :
#include <iostream>
#include "burrito.h"
using namespace std;
int main()
{
burrito a;
a.setName("Ammar T.");
return 0;
}
My class header (burrito.h)
#ifndef BURRITO_H
#define BURRITO_H
class burrito
{
public:
burrito();
};
#endif // BURRITO_H
My class file (burrito.cpp):
#include "burrito.h"
#include <iostream>
using namespace std;
burrito::setName()
{
public:
void setName(string x){
name = x;
};
burrito::getName(){
string getName(){
return name;
};
}
burrito::variables(string name){
string name;
};
private:
string name;
};
Your code is a mess. You need to write function prototypes in the header file and function definitions in the cpp file. You are missing some basic coding structures. See below and learn this pattern of coding:
This code should work and enjoy burritos !
main():
#include <iostream>
#include "Header.h"
int main()
{
burrito a;
a.setName("Ammar T.");
std::cout << a.getName() << "\n";
getchar();
return 0;
}
CPP file:
#include "Header.h"
#include <string>
void burrito::setName(std::string x) { this->name = x; }
std::string burrito::getName() { return this->name; }
Header file:
#include <string>
class burrito
{
private:
std::string name;
public:
void setName(std::string);
std::string getName();
//variables(string name) {string name;} // What do you mean by this??
};
Your poor little burrito is confused. Confused burritos can't help much.
You may want your burrito declaration as:
class Burrito
{
public:
Burrito();
void set_name(const std::string& new_name);
std::string get_name() const;
private:
std::string name;
};
The methods could be defined in the source file as:
void
Burrito::set_name(const std::string& new_name)
{
name = new_name;
}
std::string
Burrito::get_name() const
{
return name;
}
The header file only has a constructor for the class. The member functions
setName(string) and getName()
are not declared in the header file and that is why you get the error.
Also, you need to specify the return type for functions.
One way to do this would be
//Header
//burrito.h
class burrito{
private:
string burrito_name;
public:
burrito();
string getName();
void setName(string);
}
//burrito.cpp
#include "burrito.h"
#include <iostream>
using namespace std;
string burrito::getName()
{
return burrito_name;
}
void burrito::setName(string bname)
{
bname =burrito_name;
}
This is a simple example for class in C++,
Save this in burrito.cpp file then compile and run it:
#include <iostream>
#include <string>
using namespace std;
class burrito {
public:
void setName(string s);
string getName();
private:
string name;
};
void burrito::setName(string s) {
name = s;
}
string burrito::getName() {
return name;
}
int main() {
burrito a;
a.setName("Ammar T.");
std::cout << a.getName() << "\n";
return 0;
}
So, I tried to make this code :
#include <iostream>
using namespace std;
class BuckysClass{
public:
void setName(string x){
name = x;
}
string getName(){
return name;
}
private:
string name;
};
int main()
{
BuckysClass bo;
bo.setName("Buckingham Palace");
cout << bo.getName();
return 0;
}
BECOMING TO A SEPARATED CLASS like this :
#include "BuckysClass.h"
#include <iostream>
#include <string>
using namespace std;
int main (){
BuckysClass bo;
bo.setName("Buckingham Palace");
cout << bo.getName();
return 0;
}
==============
#ifndef BUCKYSCLASS_H
#define BUCKYSCLASS_H
class BuckysClass
{
public:
void setName(string x);
string getName();
private:
string name;
};
#endif // BUCKYSCLASS_H
=============
#include "BuckysClass.h"
#include <iostream>
#include <string>
using namespace std;
BuckysClass::BuckysClass()
{
}
void setName(string x){
name = x;
}
string getName(){
return name;
}
When I run the first code, I succeed,
but I got error when running the separated class code,
help me find out what's wrong ???
I tried to use different code,
but it seems I can't find the reason,
the closest reason I believe, is the main doesnt call the function on the separated class properly.
If you write this code:
void setName(string x){
name = x;
}
string getName(){
return name;
}
The compiler interprete it as two functions called setName and getName, it has no idea they are member functions of your BuckysClass class.
You have to precise it with the following syntax:
void BuckysClass::setName(string x){
name = x;
}
string BuckysClass::getName(){
return name;
}
Additionally, here you are defining a default constructor:
BuckysClass::BuckysClass()
{
}
But you didn't put it in the class prototype. You have to add it somewhere in the class prototype definition in your .h file, or your compiler won't recognize it:
class BuckysClass
{
public:
BuckysClass(); // Default constructor.
void setName(string x);
string getName();
private:
string name;
};
Friend functions can't access variables of the classes
I'm having a problem with several friend functions not being able to access the variables in classes where they have been declared as friends.
The actual error text is:
error: 'fid' was not declared in this scope. this repeats for the other private variables.
The same error is given for three functions, read, negative, and write.
A couple of notes:
1) This lab requires that I write the code so that the functions can be used by both classes.
I'm compiling this in windows with code::blocks using g++ and I've also tried compiling my code in ubuntu using g++ from the terminal using the -g flag and I get the same error both times.
Any suggestions you have would be greatly appreciated.
Header File
#ifndef PXMUTILS_H
#define PXMUTILS_H
#include <cstdio>
#include <cstdlib>
#include <string>
#include <sstream>
#include <vector>
#include <iostream>
#include <fstream>
#include <stdio.h>
#include <string.h>
using namespace std;
typedef unsigned char uchar;
class pgm
{
public:
pgm();
~pgm();
void read(string &);
void negative();
void write(string);
friend void read (const string &);
friend void write(string);
friend void negative();
private:
int nr;
int nc;
int mval;
int ftyp;
string fid;
uchar **img;
};
class ppm
{
public:
ppm();
~ppm();
void read(string &);
void negative();
void write(string);
friend void read (const string &);
friend void write (string);
friend void negative ();
private:
int nr;
int nc;
int mval;
int ftyp;
string fid;
uchar **img;
};
#endif
C++ program
#include <cstdio>
#include <cstdlib>
#include <string>
#include <sstream>
#include <vector>
#include <iostream>
#include <fstream>
#include <stdio.h>
#include <string.h>
#include "pxmutils.h"
using namespace std;
typedef unsigned char uchar;
uchar ** newimg(int nr, int nc, int ftyp)
{
uchar **img=new uchar *[nr];
img[0]=new uchar [nr*nc*ftyp];
for(int i=1; i<nr; i++)
{
img[i]=img[i-1]+nc*ftyp;
}
return img;
}
void deleteimg(uchar **img)
{
if(img)
{
if(img[0])
{
delete [] img[0];
}
delete [] img;
}
}
void read (const string &fname)
{
ifstream fin(fname.c_str(), ios::in);
if(!fin.is_open())
{
cerr<<"Could not open "<<fname<<endl;
exit(0);
}
fin >>fid
>>nc
>>nr
>>mval;
while (fin.get() != '\n') { /*skip to EOL */ }
img=newimg(nr, nc);
fin.read((char *)img[0], nr*nc);
fin.close();
}
void set_cmap(string mname)
{
}
void negative()
{
for(int i=0; i<nr; i++)
{
for(int j=0; j<nc; j++)
{
int t=img[i][j];
img[i][j]=(255-t);
}
}
}
void write(string fname)
{
ofstream fout (fname.c_str(), ios::out);
size_t dp;
if ((dp = fname.rfind(".pgm")) != string::npos)
{
fout<<"P5"<<endl;
}
if((dp= fname.rfind(".ppm")) != string::npos)
{
fout<<"P6"<<endl;
}
fout<<nc<<" "<<nr<<endl;
fout<<mval<<endl;
for(int i=0; i <nr; i++)
{
for (int j=0; j<nc; j++)
{
fout<<img[i][j]<<" ";
}
fout<<endl;
}
fout.close();
}
pgm::pgm()
{
nr=0;
nc=0;
mval=0;
ftyp=1;
fid="";
img=NULL;
}
pgm::~pgm()
{
deleteimg(img);
}
ppm::ppm()
{
nr=0;
nc=0;
mval=0;
ftyp=1;
fid="";
img=NULL;
}
ppm::~ppm()
{
deleteimg(img);
}
Program to test functions
#include <cstdlib>
#include <iostream>
#include <string>
using namespace std;
#include "pxmutils.h"
int main(int argc, char *argv[])
{
if (argc == 1) {
cerr << "No input file specified!\n";
exit(0);
}
string fname = argv[1];
size_t dp;
if ((dp = fname.rfind(".pgm")) == string::npos) {
cout << "PGM error: file suffix " << fname
<< " not recognized\n";
exit(0);
}
fname.erase(dp);
pgm img_g;
ppm img_c;
img_g.read(fname+".pgm");
if (argc == 3)
img_c.set_cmap(argv[2]);
img_c = img_g;
img_g.negative();
img_g.write(fname+"_n.pgm");
img_c.write(fname+"_c.ppm");
}
fin >>fid
>>nc
>>nr
>>mval;
while (fin.get() != '\n') { /*skip to EOL */ }
In this code, fid, nc, nr etc are undefined. You need to use the class instance to be able to access them, they don't exist by themselves.
Your functions don't accept the class objects as parameters, so how are you going to read into them?
You should have another think of your design. It is best to avoid friend functions if possible,
You need to go a bit back to basics. When you define non-static members of a class you are defining attributes or operations of the objects of the class, but those attributes don't exist by themselves, only as part of the instances of the class.
This concept is orthogonal to access and access specifiers, that is, this is so regardless of the members being public, protected or private. Once you have an instance, when your try to access those members the access specifiers come into play, and there is where friendship comes into play: it will grant your code access to members that would otherwise be inaccessible (private or protected outside of the inheritance hierarchy).
The problem in your code is that you don't have an object, and thus cannot access the members of the object. You will need to either create or pass an object of the appropriate type to the functions.
There are other problems in the code, like for example, the memory allocations inside newimg look a little suspicious (what were you intending to allocate?) but that is outside of the scope of this question.