Im using vscode and im new to c++. I learned how to create a header file link to its cpp and use it to main.cpp. The only problem bugs me out is why it causes an error this is my simple code.
Name.h
#include <iostream>
#include <string>
class myname
{
public:
void setname(std::string name);
void prname();
private:
std::string Name;
};
Name.cpp
#include "Name.h"
void myname::setname(std::string name)
{
Name = name;
}
void myname::prname()
{
std::cout<<"Hello :"<<Name<<std::endl;
}
Maiin.cpp
#include <iostream>
#include <string>
#include "Name.h"
using std::cout;
using std::string;
using std::endl;
int main()
{
myname Epoy; // IN FUNCTION INT MAIN: ERROR myname was not declared in this scope
Epoy.setname("Jomar"); //note myname <-rename "BUT THIS IS NOT THE ERROR CAUSE THIS JUST HAPPEN BECAUSE OF THE ERROR ABOVE "
Epoy.prname();
return 0;
}
also i tried so many method i even compiled this by using g++ Maiin.cpp Name.cpp - o Maiin
Still didnt work
Edit: Community want me to add more details.
What I asked was, have you write header guards in your header file: #ifndef Name_H, #define Name_H, #endif ? Since you use vscode you have to done it manually.
Like this:
#ifndef Name_H
#define Name_H
#include <iostream>
#include <string>
class myname
{
public:
void setname(std::string name);
void prname();
private:
std::string Name;
};
#endif
you missing a C++ constructor:
class Foo {
public:
Foo() { /* your init code */ } // <-- this is a std. C++ constructor
~Foo() { /* your clean-up code */ } // <-- this is a std. C++ de-structor
};
int main(int argc, char **argv) {
Foo bar; // here, you don't need the: ( ) object on heap !
}
Related
main.cpp
#include <iostream>
#include "shreeman.h"
using namespace std;
int main(){
Shreeman object;
}
shreeman.h
#ifndef SHREEMAN_H
#define SHREEMAN_H
class Shreeman
{
public:
shreeman();
};
#endif // SHREEMAN_H
shreeman.cpp
#include <iostream>
#include "shreeman.h"
using namespace std;
Shreeman::shreeman()
{
cout<<"Hello Hello"<<endl;
}
Why does this code not output "Hello Hello"? I have created an object in the main.cpp file, yet nothing is printed in the console.
In the Shreeman class, shreeman() (lowercase s) is not a valid constructor, it is just a member method. It needs to be renamed to Shreeman() (uppercase S) to be a construcor (the compiler should have warned you about that). C++ is case-sensitive, and a constructor name needs to match the class name exactly, case and all.
main.cpp
#include "shreeman.h"
int main()
{
Shreeman object;
}
shreeman.h
#ifndef SHREEMAN_H
#define SHREEMAN_H
class Shreeman
{
public:
Shreeman();
};
#endif // SHREEMAN_H
shreeman.cpp
#include <iostream>
#include "shreeman.h"
using namespace std;
Shreeman::Shreeman()
{
cout << "Hello Hello" << endl;
}
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.
I am new to c++ but have had some experience with java. I am trying to create a class but when i attempt to make a new method in the class I get several error (this is my .cpp file)
//.cpp file
#include "Test.h"
#include "Test.h"
#include <iostream>//unresolved inclusion
using namespace std;
void speak() {
if (happy) {//Symbol hapy could not be resolved
cout << "Meouw!" << endl;
} else {
cout << "Ssssss!" << endl;
}
}
void Test::makeHappy() { // member decleration not found
happy = true;//Symbol hapy could not be resolved
}
void Test::makeSad() { // member decleration not found
happy = false;//Symbol hapy could not be resolved
}
I dont get any errors in my heder file but have included it just in case
#ifndef TEST_H_
#define TEST_H_
class Test {
private:
bool happy;
public:
void makeHappy();
void makeSad();
void speak();
};
#endif /* TEST_H_ */
Finally I have another .cpp file I use which also gets errors
#include <iostream>//unresolved inclusion
#include "Test.h"
#include "Test.cpp"
using namespace std;
int main() {
Test jim;
jim.makeHappy();//method make happy could not be resolved
jim.speak();//method speak could not be resolved
Test bob;
bob.makeSad();//method make happy could not be resolved
bob.speak();//method speak could not be resolved
return 0;
}
This is the new error message I get when compiling
<!-- begin snippet: js hide: false -->
Sorry if this question is to open ended but I just cannot seem to find answers elsewhere.
this is your header file Test.h:
happy member was named bhappy_
for a private member think to add a getter and setter public member functions
#ifndef TEST_H_
#define TEST_H_
class Test {
private:
bool bhappy_;
public:
Test() // ctor
virtual ~Test() // dtor
public:
void makeHappy();
void makeSad();
void speak();
};
#endif /* TEST_H_ */
this is your Test.cpp file:
It's not advised to use using namespace std;
Don't include your header two times
//.cpp file
#include "Test.h"
#include <iostream>//unresolved inclusion
//ctor
Test::Test() : bhappy_(false)
{}
Test::~Test(){}
void Test::speak() {
if (bhappy_) {//Symbol hapy could not be resolved
std::cout << "Meouw!" << endl;
} else {
std::cout << "Ssssss!" << endl;
}
}
void Test::makeHappy() {
bhappy_ = true;//Symbol hapy could not be resolved
}
void Test::makeSad() { // member decleration not found
bhappy_ = false;//Symbol hapy could not be resolved
}
This is your main function:
#include "Test.h"
int main(int argc, char** argv) {
Test jim;
jim.makeHappy();//method make happy could not be resolved
jim.speak();//method speak could not be resolved
Test bob;
bob.makeSad();//method make happy could not be resolved
bob.speak();//method speak could not be resolved
return 0;
}
You need specify Test::speak().
Take should use this. to use class attribut. Think about getter and setter.
And finally, look C++ training, it should be usefull ^^ .
See you.
I've got a third party library named person.lib and its header person.h. This is my actual project structure and it compiles and runs perfectly.
Actual Structure:
main.cpp
#include <iostream>
#include <time.h>
#include <ctype.h>
#include <string>
#include "person.h"
using namespace person;
using namespace std;
class Client : public Person
{
public:
Client();
void onMessage(const char * const);
private:
void gen_random(char*, const int);
};
Client::Client() {
char str[11];
gen_random(str, 10);
this->setName(str);
}
void Client::onMessage(const char * const message) throw(Exception &)
{
cout << message << endl;
}
void Client::gen_random(char *s, const int len) {
//THIS FUNCTION GENERATES A RANDOM NAME WITH SPECIFIED LENGTH FOR THE CLIENT
}
int main()
{
try
{
Person *p = new Client;
p->sayHello();
}
catch(Exception &e)
{
cout << e.what() << endl;
return 1;
}
return 0;
}
I want to refactor my code by dividing the declaration of my Client class from its definition and create client.h and client.cpp. PAY ATTENTION: sayHello() and onMessage(const * char const) are functions of the person library.
Refactored Structure:
main.cpp
#include <iostream>
#include "client.h"
using namespace person;
using namespace std;
int main()
{
try
{
Person *p = new Client;
p->sayHello();
}
catch(Exception &e)
{
cout << e.what() << endl;
return 1;
}
return 0;
}
client.cpp
#include "client.h"
using namespace person;
using namespace std;
Client::Client() {
char str[11];
gen_random(str, 10);
this->setName(str);
}
void Client::onMessage(const char * const message) throw(Exception &)
{
cout << message << endl;
}
void Client::gen_random(char *s, const int len) {
//THIS FUNCTION GENERATES A RANDOM NAME WITH SPECIFIED LENGTH FOR THE CLIENT
}
client.h
#ifndef CLIENT_H
#define CLIENT_H
#include <time.h>
#include <ctype.h>
#include <string>
#include "person.h"
class Client : public Person
{
public:
Client();
void onMessage(const char * const);
private:
void gen_random(char*, const int);
};
#endif
As you can see, I've simply created a client.h in which there's the inclusion of the base class person.h, then I've created client.cpp in which there's the inclusion of client.h and the definitions of its functions. Now, the compilation gives me these errors:
error C2504: 'Person': base class undefined client.h 7 1 Test
error C2440: 'inizialization': unable to convert from 'Client *' to 'person::impl::Person *' main.cpp 15 1 Test
error C2504: 'Person': base class undefined client.h 7 1 Test
error C2039: 'setName': is not a member of 'Client' client.cpp 8 1 Test
error C3861: 'sendMessage': identifier not found client.cpp 34 1 Test
It's a merely cut© refactoring but it doesn't work and I really don't understand WHY! What's the solution and why it gives me these errors? Is there something about C++ structure that I'm missing?
Here's a dog-n-bird implementation (ruff ruff, cheep cheep)
cLawyer is defined and implemented in main.cpp, while cPerson and cClient are defined in their own header files, implemented in their own cpp file.
A better approach would store the name of the class. Then, one wouldn't need to overload the speak method - one could simply set the className in each derived copy. But that would have provided in my estimates, a less useful example for you.
main.cpp
#include <cstdio>
#include "cClient.h"
class cLawyer : public cPerson
{
public:
cLawyer() : cPerson() {}
~cLawyer() {}
void talk(char *sayWhat){printf("cLawyer says: '%s'\n", sayWhat);}
};
int main()
{
cPerson newPerson;
cClient newClient;
cLawyer newLawyer;
newPerson.talk("Hello world!");
newClient.talk("Hello world!");
newLawyer.talk("Hello $$$");
return 0;
}
cPerson.h
#ifndef cPerson_h_
#define cPerson_h_
class cPerson
{
public:
cPerson();
virtual ~cPerson();
virtual void talk(char *sayWhat);
protected:
private:
};
#endif // cPerson_h_
cPerson.cpp
#include "cPerson.h"
#include <cstdio>
cPerson::cPerson()
{
//ctor
}
cPerson::~cPerson()
{
//dtor
}
void cPerson::talk(char *sayWhat)
{
printf("cPerson says: '%s'\n",sayWhat);
}
cClient.h
#ifndef cClient_h_
#define cClient_h_
#include "cPerson.h"
class cClient : public cPerson
{
public:
cClient();
virtual ~cClient();
void talk(char *sayWhat);
protected:
private:
};
#endif // cClient_h_
cClient.cpp
#include "cClient.h"
#include <cstdio>
cClient::cClient()
{
//ctor
}
cClient::~cClient()
{
//dtor
}
Output
cPerson says: 'Hello world!'
cClient says: 'Hello world!'
cLawyer says: 'Hello $$$'
Suggestions noted above:
//In the cPerson class, a var
char *m_className;
//In the cPerson::cPerson constructer, set the var
m_className = "cPerson";
//Re-jig the cPerson::speak method
void cPerson::speak(char *sayWhat)
{
printf("%s says: '%s'\n", m_className, sayWhat);
}
// EDIT: *** remove the speak methods from the cClient and cLawyer classes ***
//Initialize the clas name apporpriately in derived classes
//cClient::cClient
m_className = "cClient";
//Initialize the clas name apporpriately in derived classes
//cLaywer::cLaywer
m_className = "cLawyer";
You are declaring the class Client twice - once in the .h file and once in .cpp. You only need to declare it in the .h file.
You also need to put the using namespace person; to the .h file.
If class Person is in namcespace person, use the person::Person to access it.
The client.cpp must contain definitions only!
I think for the linker the class Client defined in client.h and class Client defined in client.cpp are different classes, thus it cannot find the implementation of Client::Client(). I purpose to remove the declaration of class Client from the client.cpp and leave there only definitions of functions:
// client.cpp
#include <time.h>
#include <ctype.h>
#include <string>
#include "client.h"
using namespace std;
Client::Client()
{
//DO STUFF
}
void Client::onMessage(const char * const message)
{
//DO STUFF
}
void Client::gen_random(char *s, const int len) {
//DO STUFF
}
I got three .cpp files and two header files.
But when i compile them, meaning the Point.cpp, Data.cpp and main.cpp, it will say
Data.h:6:7 redefinition of Data at 'Data.h'
Data.h:6:7 previously definition of 'class Data'
Below is my Data.h(previously known as 2.h at above)
#include <iostream>
#include <string>
using namespace std;
class Data
{
private:
string sType;
public:
Data();
Data(string);
void setSType(string);
string getSType();
};
Below is my data.cpp
#include "Data.h"
Data::Data()
{
sType = "";
}
Data::Data(string s)
{
sType = s;
}
void Data::setSType(string ss)
{
sType = ss;
}
string Data::getSType()
{
return sType;
}
Below is my PointD.h (previously known as 3.h)
#include <iostream>
#include <string>
#include "Data.h"
using namespace std;
class PointD
{
private:
int x
Data data1;
public:
PointD();
PointD(int,Data);
void setX(int);
void setData(Data);
int getX();
Data getData();
};
Below is my PointD.cpp
#include "PointD.h"
PointD::PointD()
{
x = 0;
}
PointD::PointD(int xOrdinate,Data dd)
{
x = xOrdinate;
data1 = dd;
}
void PointD::setXordinate(int Xordinate)
{
x = Xordinate;
}
void PointD::setData(Data dd)
{
data1 = dd;
};
int PointD::getXordinate()
{
return x;
}
Data PointD::getData()
{
return data1;
}
This is my main.cpp
#include <iostream>
#include <string>
#include "Data.h"
#include "PointD.h"
using namespace std;
int main()
{
const int MAX_NUM = 20;
Data ldata[MAX_NUM];
PointD pointd[MAX_NUM];
//more codes..
}
But when i compile them, meaning the Point.cpp, Data.cpp and main.cpp, it will say
Data.h:6:7 redefinition of Data at 'Data.h'
Data.h:6:7 previously definition of 'class Data'
Can anybody let me know whats actually went wrong here..
You need to use include guards, or the easiest:
#pragma once
in your header files
See Purpose of Header guards for more background
Idea: 1.hpp
#ifndef HEADER_GUARD_H1_HPP__
#define HEADER_GUARD_H1_HPP__
// proceed to declare ClassOne
#endif // HEADER_GUARD_H1_HPP__
In each of your header files write:
#ifndef MYHEADERNAME_H
#define MYHEADERNAME_H
code goes here....
#endif
Its better like this:
#ifndef DATA_H /* Added */
#define DATA_H /* Added */
#include <iostream>
#include <string>
// using namespace std; /* Removed */
class Data
{
private:
std::string sType;
public:
Data();
Data( std::string const& ); // Prevent copy of string object.
void setSType( std::string& ); // Prevent copy of string object.
std::string const& getSType() const; // prevent copy on return
std::string& getSType(); // prevent copy on return
};
#endif /* DATA_H */
The big fix is adding ifndef,define,endif. The #include directive works as if copying and pasting the .h to that line. In your case the include from main.cpp are:
main.cpp
-> Data.h (1)
-> Point.h
-> Data.h (2)
At (2), Data.h has already been `pasted' into main.cpp at (1). The class declaration of Data, i.e. "class Data{ .... };" , appears twice. This is an error.
Adding include guards to the top and bottom of every .h are standard practice to avoid this problem. Don't think about it. Just do it.
Another change I'd suggest is to remove any "using namespace ..." lines from any .h . This breaks the purpose of namespaces, which is to place names into separate groups so that they are not ambiguous in cases where someone else wants an object or function with the same name. This is not an error in your program, but is an error waiting to happen.
For example, if we have:
xstring.h:
namespace xnames
{
class string
{
...
};
}
Foo.h
#include <xstring>
using namespace xnames;
...
test.cxx:
#include "Foo.h"
#include "Data.h" // Breaks at: Data( string ); -- std::string or xnames::string?
...
void test()
{
string x; // Breaks. // std::string or xnames::string?
}
Here the compiler no longer knows whether you mean xnames::string or std::string. This fails in test.cxx, which is fixable by being more specific:
void test()
{
std::string x;
}
However, this compilation still now breaks in Data.h. Therefore, if you provide that header file to someone, there will be cases when it is incompatible with their code and only fixable by changing your header files and removing the "using namespace ...;" lines.
Again, this is just good coding style. Don't think about it. Just do it.
Also, in my version of Data.h, I've changed the method parameters and return types to be references (with the &). This prevents the object and all of its state from being copied. Some clever-clogs will point our that the string class's is implementation prevents this by being copy-on-write. Maybe so, but in general, use references when passing or returning objects. It just better coding style. Get in the habit of doing it.