I am getting the following error with g++ 4.9:
basis.cpp:16: undefined reference to `Basis::foo(int, int)'
This is the header file:
#ifndef BASIS_H
#define BASIS_H
#include "common.h"
#include <math.h>
#include "xdouble.h"
using namespace std;
class Basis {
private:
int rank;
int dim;
public:
Basis(); //Empty constructor
Basis(int r, int d); //Default constructor
void foo(int a, int b);
void bar(int a, int b);
};
#endif
The basis.cpp file is the following:
#include "basis.h"
Basis::Basis()
{
rank = 0;
dim = 0;
}
Basis::Basis(int r, int d) // Default constructor
{
rank = r;
dim = d;
}
void Basis::bar(int a, int b)
{
void foo(int a, int b);
}
void Basis::foo(int a, int b)
{
}
Even though I'm including the basis.h file I get the undefined reference error and I can't understand why this is happening. What am I doing wrong?
Thanks
It looks like a copy and paste error. Try this:
void Basis::bar(int a, int b)
{
foo(a, b);
}
You made a mistake because you copied and pasted the definition of the function foo in the place where you wanted to call this function.
Related
I have two different header file and one main file.
headerfile 1 : env.h
#include <math.h>
struct env
{
env(int a, int b)
{
/*data*/
}
auto add(int a, int b)
{
return a+b;
}
};
headerfile 2 : Myclass.h
#include <random>
class myclass
{
static auto dot(int a, int b, env& E) -> int;
}
myclass::dot(int a, int b, env& E) -> int
{
int temp = E.add(a,b);
return temp;
}
main file : main.cpp
#include <env.h>
int main(){
int a = 5;
int b = 6;
env E(a, b);
int c = myclass::dot(a, b, E)
return 0;
}
What i would like to do is to parse the class definition(env E) in main file into the construction(myclass::dot()) of other class(myclass). But i am getting the error as "declaration is incompatible with myclass::dot". What i think is that Myclass.h does not know the value type of struct env. So how to define the class in Myclass.h.
Thanks in advance.
I just noticed something when creating functions. In the code:
#include <iostream>
using namespace std;
int add(int a, int b = 20)
{
int r;
r = a + b;
return (r);
}
int main()
{
int result;
result = add(20);
cout<<result;
return 0;
}
it will work because the function being called is on top of the caller, but if I put the function add() below the calling function in main() it won't work.
#include <iostream>
using namespace std;
int main()
{
int result;
result = add(20);
cout<<result;
return 0;
}
int add(int a, int b = 20)
{
int r;
r = a + b;
return (r);
}
and the compiler will tell me that the identifier add() cannot be found.
so why do we declare functions anyway? like this:
#include <iostream>
using namespace std;
int add(int a, int b = 20);
int main()
{
int result;
result = add(20);
cout<<result;
return 0;
}
int add(int a, int b)
{
int r;
r = a + b;
return (r);
}
A definition is implicitly a declaration. And a declaration must come ahead of the use.
All functions need to be declared before they are used.
You can do that by either (1) writing a declaration, or (2) writing a definition.
Relying solely on (2) can be tempting but then you are bound to order your program in a particular way, and is occasionally impossible. For example, the following will not compile unless the comment is removed.
//void bar(int);
void foo(int n)
{
if (!n){
bar(n);
}
}
void bar(int n)
if (n){
foo(n);
}
}
int main()
{
foo(1);
}
No.
If the function definition appears before the function call, then prototype is not mandatory. Otherwise function prototype is necessary to let compiler know how to respond to a function when it is called.
A function declaration tells the compiler about a function's name, return type, and parameters. A function definition provides the actual body of the function.
if the function definition appears after the function call then prototype is mandatory. because it tells the compiler to how to respond the function when it is called.
check the following example.
/* C++ Function Prototype and C++ Function Definition */
#include<iostream.h>
#include<conio.h>
#include<stdlib.h>
int add(int, int); // function prototype
void main()
{
clrscr();
int a, b;
cout<<"Enter any two number: ";
cin>>a>>b;
cout<<"\nSummation = "<<add(a, b);
getch();
}
int add(int x, int y) // function definition
{
int res;
res = x + y;
return res;
}
and if the function definition is made before the function call then it is not mandatory to declare function prototype.
consider example.
/* C++ Function Prototype and C++ Function Definition */
#include<iostream.h>
#include<conio.h>
#include<stdlib.h>
int add(int x, int y) // function definition
{
int res;
res = x + y;
return res;
}
void main()
{
clrscr();
int a, b;
cout<<"Enter any two number: ";
cin>>a>>b;
cout<<"\nSummation = "<<add(a, b);
getch();
}
I have the following problem.
I have a base abstract class with a pure virtual method, and I want to pass it as an argument to another member function(so not a normal function). Yet I have an error when trying to call the method with specified function. Code speaks better than words so bellow I have posted the code that generates the problem
class BaseClass
{
public:
BaseClass();
int add(int, int);
virtual void op(void (*f)(int, int), string s, int a, int b) = 0;
~BaseClass();
};
#include "BaseClass.h"
class ClasaDerviata:public BaseClass
{
public:
ClasaDerviata();
void testNumere(int a, int b);
void op(void(*f)(int, int), string s, int a, int b);
~ClasaDerviata();
};
#include "BaseClass.h"
BaseClass::BaseClass()
{
}
int BaseClass::add(int a, int b)
{
return a + b;
}
BaseClass::~BaseClass()
{
}
#include "ClasaDerviata.h"
#include <iostream>
using namespace std;
ClasaDerviata::ClasaDerviata()
{
}
void ClasaDerviata::testNumere(int a, int b)
{
cout << a + b << "\n";
cout << " suma " << add(a,b) << "\n";
}
void ClasaDerviata :: op (void (*f)(int, int), string s, int a, int b)
{
f(a, b);
cout << s << "\n";
}
ClasaDerviata::~ClasaDerviata()
{
}
#include "ClasaDerviata.h"
#include <iostream>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
ClasaDerviata *a;
a = new ClasaDerviata();
int x, y;
cin >> x >> y;
a->op(&ClasaDerviata::testNumere, "test metoda", x, y);
system("pause");
return 0;
}
Thank you for your time!
void ClasaDerviata::testNumere(int a, int b); is not of type void (*)(int, int) but void (ClasaDerviata::*)(int, int)
You may add static to testNumere and add to fix your problem or change signature of your function (and change internal code too).
Remember when you make a call to a member function a hidden parameter 'this' is passed. So your ClasaDerviata::testNumere(int a, int b); function actually takes three parameters.
I would suggest to read Joseph Garvin comment in
How can I pass a class member function as a callback?
he has explained it very well.
I have a simple class which I cannot instantiate and I don't know why...
Please help me !
-------Test.cpp-------
#include<iostream>
using namespace std;
#include "meteo.h"
int main()
{
Meteo meteo;
}
-------meteo.h---------
#ifndef METEO_H
#define METEO_H
class Meteo
{
public:
Meteo();
int Get(int i);
private:
char *list[];
};
#endif
-------meteo.cpp--------
#include "meteo.h"
Meteo::Meteo()
{
list[]("Sec","Venteux","Humide");
}
int Meteo::Get(int i)
{
return list[i];
}
I get the error: "undefined reference to `Meteo::Meteo()'"
It seems that the problem is that the compiler issued an error when was compiling the constructor
Meteo::Meteo()
{
list[]("Sec","Venteux","Humide");
}
and did not generate the object module.
This record
list[]("Sec","Venteux","Humide");
is invalid.
Try to change the class definition like
class Meteo
{
public:
Meteo();
int Get(int i);
private:
const char *list[3];
};
and define the constructor like
Meteo::Meteo() : list { "Sec","Venteux","Humide" }
{
}
The other reason might be that you did not include object module meteo in the project.
Take into account that this member function
int Meteo::Get(int i)
{
return list[i];
}
is also wrong. The type of elements of the array is const char * not int.
I got an error while compiling C++:
/tmp/ccqs6UN2.o: In function main': PowerModulus.cpp:(.text+0x194): undefined reference to takeModulusLOOP(int, int, int)' collect2: ld returned 1 exit status
The source code:
#include "PowerModulus.h"
#include <iostream>
int modint(int x, int moduint);
int takeModulusLOOP(int x, int n, int moduint);
int main() {
std::cout << takeModulusLOOP(5348, 700, 335);
}
int PowerModulus::takeModulusLOOP(int x, int n, int moduint) {
int total = modint(x, moduint);
n--;
while (--n) {
total = modint(total * x, moduint);
}
return total;
}
int PowerModulus::modint(int x, int moduint) {
while (x < 0) // Deal with negative
x += moduint;
return x % moduint; // Comes out positive now -> %
}
PowerModulus::PowerModulus() {
// TODO Auto-generated constructor stub
}
PowerModulus::~PowerModulus() {
// TODO Auto-generated destructor stub
}
Header file:
#ifndef POWERMODULUS_H_
#define POWERMODULUS_H_
int modint(int x, int moduint);
int takeModulusLOOP(int x, int n, int moduint);
class PowerModulus {
public:
int takeModulusLOOP(int x, int n, int moduint);
int modint(int x, int moduint);
PowerModulus();
virtual ~PowerModulus();
};
#endif /* POWERMODULUS_H_ */
Where is the error?
You have declared a global takeModulusLOOP function, then call it in main, without ever defining it. This is a different function than PowerModulus::takeModulusLOOP.
// main.cpp
#include "PowerModulus.h"
#include <iostream>
int main(){
std::cout << PowerModulus::takeModulusLOOP(5348,700,335) << '\n';
return 0;
}
Changed to a namespace instead of a class, and separated into header and implementation (instead of grouping in main.cpp):
// PowerModulus.cpp
#include "PowerModulus.h"
namespace PowerModulus {
int takeModulusLOOP(int x, int n, int moduint){
int total = modint(x, moduint) ;
n--;
while (--n){
total = modint( total * x, moduint );
}
return total;
}
int modint(int x, int moduint){
while ( x < 0) // deal with negative
x += moduint;
return x % moduint;//comes out positive now -> %
}
}
Header:
// PowerModulus.h
#ifndef POWERMODULUS_H_
#define POWERMODULUS_H_
namespace PowerModulus {
int modint(int x, int moduint);
int takeModulusLOOP(int x, int n, int moduint);
}
#endif
This line:
std::cout << takeModulusLOOP(5348,700,335);
is calling the non-class takeModulusLOOP, which you haven't defined anywhere.
You should either call the class version, by providing an object of the class type and using something like:
PowerModulus p;
std::cout << p.takeModulusLOOP(5348,700,335);
(most likely) or providing a non-class version (least likely).
You could also consider making the function static since it doesn't seem to require an object at all. Then you don't need to instantiate one.
You receive the error, because you do not have such a function.
Actually, you have it in PowerModulus class, so you should call the function from PowerModulus instance.
PowerModulus pM;
pM.takeModulusLoop(5348,700,335);
You do not need to claim the function in the beginning of your .h file or in the beginning of your .cpp file.
If you intended to use the takeModulusLoop function of the PowerModulus class then you need not declare a global function again...
But, if you intended to use a different global function, then you need to define it in its context...