I've gone through many similar threads on this kind of question but I'm still unable to resolve this error. Any help would be appreciated.
/*samp.h header file*/
#include<iostream>
using namespace std;
class test
{
private:
test();
public:
static void const_caller();
};
/*samp.cpp file*/
#include<iostream>
using namespace std;
class test
{
private:
test()
{
cout<<"priv cont called\n";
}
public:
static void const_caller()
{
cout<<"calling priv const\n";
}
};
/*main.cpp file */
#include"samp.h"
using namespace std;
int main(int argc, char **argv)
{
test::const_caller();
}
when I do
g++ samp.cpp main.cpp -o main.out
I get this error
/usr/bin/ld: /tmp/ccHZVIBK.o: in function `main':
main.cpp:(.text+0x14): undefined reference to `test::const_caller()'
which I'm unable to resolve since quite some time now.
In the samp.cpp file you define test class again.
You need to include samp.h header and implement methods of test class:
#include "samp.h"
using namespace std;
test::test()
{
cout << "priv cont called\n";
}
void test::const_caller()
{
cout << "calling priv const\n";
}
With your posted code, the .cpp file contains its own definition of the class that has the same name as the class in the .h file but it is really a different class.
In the .cpp file, you need to use:
test::test()
{
cout<<"priv cont called\n";
}
void test::const_caller()
{
cout<<"calling priv const\n";
}
Related
I am learning C++ and currently testing inline functions. If I run my code now I will have linking error, but if I change
inline void Test::print40()
to
void Test::print40()
everything would be fine. Could you explain to me why I have an error and how to use inline function in this case.
// main.cpp file
#include "Test.h"
using namespace std;
int main()
{
Test obj1;
obj1.print40();
}
// Test.cpp file
#include <iostream>
#include "Test.h"
inline void Test::print40()
{
std::cout << "40";
}
// Test.h file
#pragma once
class Test
{
public:
void print40();
};
Inline function definition shall be in each compilation unit where it is ODR used.
On the other hand in your project the compilation unit main does not know that the function is an inline function. So it can not find its definition.
Move this definition from Test.cpp
#pragma once
class Test
{
public:
void print40();
};
inline void Test::print40()
{
std::cout << "40";
}
to the header Test.h.
The module Test.cpp is redundant.
As the function is very simple and short then it could be defined in the class definition as for example
class Test
{
public:
void print40()
{
std::cout << "40";
}
};
In this case it will be an inline function by default.
I have a programming assignment where I'm supposed to write up the code for inserting and removing linked lists. However I haven't used C++ in a while and am struggling remember certain things.
Right now, I am simply trying to put a prototype method in a header file, define it in my cpp file, and then call it in my main method. this is what I have.
LinkedList.h
#include <iostream>
using namespace std;
class LinkedList {
public:
void testPrint();
};
LinkedList.cpp
#include "LinkedList.h"
int main() {
LinkedList::testPrint();
}
void LinkedList::testPrint() {
cout << "Test" << endl;
}
I am getting the following errors
a nonstatic member reference must be relative to a specific object
'LinkedList::testPrint': non-standard syntax; use & to create a pointer to member
LinkedList::testPrint() is a member function.
It is not declared static, so that means it must be called on a particular object, defined as LinkedList linked_list, for example. Then use linked_list.testPrint().
Option 1 - static member function declaration
#include <iostream>
using namespace std;
class LinkedList {
public:
static void testPrint();
};
int main() {
LinkedList::testPrint();
}
void LinkedList::testPrint() {
cout << "Test" << endl;
}
Option 2 - Instantiated object with call to member function
#include <iostream>
using namespace std;
class LinkedList {
public:
void testPrint();
};
int main() {
LinkedList linked_list;
linked_list.testPrint();
}
void LinkedList::testPrint() {
cout << "Test" << endl;
}
**PROBLEM SOLVED. It appears that i had created an extra header by mistake, and since i deleted him , it worked. **
So i am trying to understand about classes and headers and how i can make them work together.
I am following an online tutorial but it seems that something is going wrong in my code.
The problem is that when i try to run the main it gives me this error:
multiple definition of Cat::speak() and all the other functions.
main.cpp
#include <iostream>
#include "class.h"
using namespace std;
int main()
{
Cat jim;
jim.makehappy();
jim.speak();
Cat george;
george.makesad();
george.speak();
return 0;
}
class.cpp
#include <iostream>
#include "class.h"
using namespace std;
void Cat::speak()
{
if (happy)
{
cout << "meoww" << endl;
}
else
{
cout << "sssss" << endl;
}
}
void Cat::makehappy()
{
happy = true;
}
void Cat::makesad()
{
happy = false;
}
class.h
#ifndef CLASS_H_INCLUDED
#define CLASS_H_INCLUDED
class Cat
{
private:
bool happy;
public:
void makehappy();
void makesad();
void speak();
};
#endif // CLASS_H_INCLUDED
From what you have shown here there should be no problems. What you could do to temporarily resolve this to find out if you are actually defining this function in several places is to wrap your class in a namespace.
class.h
#ifndef CLASS_H_INCLUDED
#define CLASS_H_INCLUDED
namespace myNamespace {
class Cat {
private:
bool happy;
public:
void makehappy();
void makesad();
void speak();
};
} // namespace myNamespace
#endif // CLASS_H_INCLUDED
class.pp
#include <iostream>
#include "class.h"
// using namespace std; // Don't Use - This is Bad Practice
// Can cause name clashing when trying to resolve name lookup
namespace myNamespace {
void Cat::speak() {
if (happy) {
std::cout << "meoww" << std::endl;
} else {
std::cout << "sssss" << std::endl;
}
}
void Cat::makehappy() {
happy = true;
}
void Cat::makesad() {
happy = false;
}
} // namespace myNamespace
main.cpp
#include <iostream>
#include "class.h"
// using namespace std; // Again -Bad Practice
int main() {
using namespace myNamespace;
Cat jim;
jim.makehappy();
jim.speak();
Cat george;
george.makesad();
george.speak();
return 0;
}
Try this to see if you are getting the same compiler error. This should help you to see if you are defining this function in multiple spaces. Also by removing the using namespace std; and just using the scope resolution operator to the std:: namespace will help to eliminate any possible problems and any possible future problems.
How are you compiling the code? You need to make sure that you are building the specific "class.o" and "main.o" files separately before linking them together. Here is an example Makefile.
all: main
main: main.o class.o
g++ main.o class.o -o main
main.o: main.cpp class.h
g++ -c main.cpp
class.o: class.cpp class.h
g++ -c class.cpp
It looks like you are using double inclusion guards so I don't think that is the problem. Check out this answer for a more in-depth explanation of what is happening: Error with multiple definitions of function
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.
Please excuse me but I didn't know to give a name to the title in a short way.
Why do I need to declare an overloaded operator inside the header to make it work in this example:
HEAD.H
#pragma once
namespace test {
class A {
public:
A() : x(0) {}
int x;
};
A& operator++(A& obj); //this is my question
}
HEAD.CPP
#include "head.h"
namespace test {
A& operator++(A& obj) {
++obj.x;
return obj;
}
}
MAIN.CPP
#include <iostream>
#include "head.h"
using namespace std;
using namespace test;
int main() {
A object;
++object; //this won't work if we delete declaration in a header
return 0;
}
operator++ is defined and declared in a namespace inside "head.cpp" so why do I need to declare it one more time in a header?
Thank you.
The CPP files are compiled independently of each other, and they only see the header files they've included (which are in fact textually added to the source code of the CPP before compilation). As such you'll use the header file to inform the compiler that a function exists with that signature (be it an operator overload).
Then the output from your CPP files is put together by the linker, which is when you'd find out if for instance you had declared a function in a header file but never taken the trouble to implement it.
Simple example with namespaces:
#include <iostream>
namespace test{
int f() { return 42; }
int g() { return -1; }
}
namespace other{
int f() { return 1024; }
}
using namespace other;
int main(){
//error: 'g' was not declared in this scope
//std::cout << g() << std::endl;
std::cout << test::f() << std::endl; //42
std::cout << f() << std::endl; //1024
return 0;
}