I can't seem to get the errors to go away. The errors are below. I have looked on Google Search and still I can't figure it out. It is not like I am new to C++, but I have not fooled around with it in a while.
The weird thing is it worked with g++ on Windows...
Errors using:
g++ main.cpp
Output:
/tmp/ccJL2ZHE.o: In function main': \ main.cpp:(.text+0x11): undefined reference to Help::Help()'
main.cpp:(.text+0x1d): undefined reference to Help::sayName()' \ main.cpp:(.text+0x2e): undefined reference to Help::~Help()'
main.cpp:(.text+0x46): undefined reference to `Help::~Help()'
collect2: ld returned 1 exit status
File main.cpp
#include <iostream>
#include "Help.h"
using namespace std;
int main () {
Help h;
h.sayName();
// ***
// ***
// ***
return 0;
}
File Help.h
#ifndef HELP_H
#define HELP_H
class Help {
public:
Help();
~Help();
void sayName();
protected:
private:
};
#endif // HELP_H
File Help.cpp
#include <iostream>
#include "Help.h"
using namespace std;
Help::Help() { // Constructor
}
Help::~Help() { // Destructor
}
void Help::sayName() {
cout << " ***************" << endl;
cout << " ************************************" << endl;
cout << " ************" << endl;
cout << " *********************" << endl;
}
Use
g++ main.cpp Help.cpp
You have to tell the compiler all the files that you want it to compile, not just the first one.
You should add help.o to your g++ line:
g++ -c help.cpp -o help.o
g++ help.o main.cpp
By splitting it to two lines you can save compilation time (in case of larger projects), because you can compile help.cpp only when it was changed. make and Makefile used well will save you a lot of headache:
#Makefile
all: main
main: help main.cpp
g++ -o main help.o main.cpp
help: help.cpp
g++ -c -o help.o help.cpp
I had the same problem with my Linux Lubuntu distribution and it was creating the problem for my constructor and destructor. It was not recognizing them.
Actually, this goes off if you just compile all of the three files together. So, once you saved all your files, just do this:
g++ main.cpp Help.h Help.cpp
./a.out
./a.out is the executable file for the Linux. Sorry, but I don't know about the Windows. And your program would run smoothly.
Related
hope you guys are doing well. I am just getting linker error in C++ , I don't know why? Everything is correct....
Check below testing.h file
#ifndef __MYClass__
#define __MYClass__
#include<iostream>
using namespace std;
class Abc {
private:
int a;
public:
void input();
void display();
};
#endif
and here's implementation of these functions in Functions.cpp file.
#include"testing.h"
void Abc::input() {
cout<<"Enter any value : ";
cin>>a;
}
void Abc::display() {
cout<<"You Entered : "<<a;
}
And now, in main.cpp
#include<iostream>
#include"testing.h"
using namespace std;
int main() {
Abc obj;
obj.input();
obj.display();
return 0;
}
All files are compiled successfully.
In main.cpp Linker says....
g++ -Wall -o "main" "main.cpp" (in directory: /home/Welcome/C++ Practices/testingLinux)
/usr/bin/ld: /tmp/ccYI9LAy.o: in function main': main.cpp:(.text+0x10): undefined reference to Abc::input()'
/usr/bin/ld: main.cpp:(.text+0x1c): undefined reference to `Abc::display()'
collect2: error: ld returned 1 exit status
Compilation failed.
I'm using built-in linux compiler...
There are multiple ways you can fix this but before that please read up on Translation Unit.
Coming to your problem.
When you write
g++ -Wall -o main main.cpp
The compiler will pick up main.cpp for compilation and expand testing.h that includes the declaration for class ABC and with this header file it can determine what is the size of ABC and be able to generate instructions reserving space for obj on the stack. It can't see the definition for input() and display() hence defers that task to the linker. Note that testing.cpp is not in the picture at all since the compiler doesn't know that the implementation of ABC is in testing.cpp. Now when the linker tries to resolve the symbols input() it fails to find the definition for it and throws the error
undefined reference to Abc::input()
So, to fix this you can tell explicitly upfront that it also needs to take in testing.cpp while compiling main.cpp by
g++ -o main main.cpp testing.cpp
Another way is to create a dynamic library out of testing.h and testing.cpp
g++ -shared -fPIC testing.cpp -o libtest
and then link it against main.cpp
g++ -o main main.cpp -I. -L. libtest
What this does is that the compiler still can't figure out the definition of input() and display() but the linker can since now the library containing the definitions is provided to it.
You are not compiling Functions.cpp file.
This should fix your issue:
g++ main.cpp Functions.cpp
this my log.cpp
file.
#include <iostream>
using namespace std;
void log(){
cout << "OMG, nothing is working...";
}
this my header file : log.h
void log();
this's my main.cpp file
#include "log.h"
int main(){
log();
return 0;
}
I want to precompile the header file I use this command
g++ log.h I get log.h.gch file
then I compile the main.cpp file using
g++ main.cpp
I get this Error :(
/tmp/cc9YGzwo.o: In function `main':
main.cpp:(.text+0x5): undefined reference to `log()'
collect2: error: ld returned 1 exit status[![help me please][1]][1]
The header declared void log(), main wants to use it, but it's missing the implementation. Link log.o to main.
g++ -c log.cpp
Then
g++ main.cpp -o main log.o
Output:
OMG, nothing is working...
I moved from Windows to Ubuntu and I wanted to try some C++ programming on Ubuntu. So here is very simple code and very stupid error which I can't resolve:
horse.h
#ifndef _horse_
#define _horse_
class Horse{
int speed;
public:
void saySomething();
};
#endif
horse.cpp
#include "horse.h"
#include <iostream>
using namespace std;
void Horse::saySomething(){
cout << "iiiihaaaaaaa brrrrr."<<endl;
}
and Main.cpp
#include "horse.h"
int main(){
Horse h;
h.saySomething();
}
After I compile (compilation is successful) and run this I get this error message:
/tmp/ccxuDyrd.o: In function `main':
Main.cpp:(.text+0x11): undefined reference to `Horse::saySomething()'
collect2: ld returned 1 exit status
Please help me somehow.
Try
g++ -c main.cpp horse.cpp (to compile)
g++ -o a.out main.o horse.o (to link)
It seems you only compiled your code but did not link the resulting object files. You probably invoked the compiler like this:
g++ main.cpp
You should instead compile every *.cpp file separately and then link each resulting *.o file. And you should do this with a Makefile.
Actually, the basic idea is the same on Windows with MSVC. The compiler produces object files, the linker links them together.
I can't seem to get the errors to go away. The errors are below. I have looked on Google Search and still I can't figure it out. It is not like I am new to C++, but I have not fooled around with it in a while.
The weird thing is it worked with g++ on Windows...
Errors using:
g++ main.cpp
Output:
/tmp/ccJL2ZHE.o: In function main': \ main.cpp:(.text+0x11): undefined reference to Help::Help()'
main.cpp:(.text+0x1d): undefined reference to Help::sayName()' \ main.cpp:(.text+0x2e): undefined reference to Help::~Help()'
main.cpp:(.text+0x46): undefined reference to `Help::~Help()'
collect2: ld returned 1 exit status
File main.cpp
#include <iostream>
#include "Help.h"
using namespace std;
int main () {
Help h;
h.sayName();
// ***
// ***
// ***
return 0;
}
File Help.h
#ifndef HELP_H
#define HELP_H
class Help {
public:
Help();
~Help();
void sayName();
protected:
private:
};
#endif // HELP_H
File Help.cpp
#include <iostream>
#include "Help.h"
using namespace std;
Help::Help() { // Constructor
}
Help::~Help() { // Destructor
}
void Help::sayName() {
cout << " ***************" << endl;
cout << " ************************************" << endl;
cout << " ************" << endl;
cout << " *********************" << endl;
}
Use
g++ main.cpp Help.cpp
You have to tell the compiler all the files that you want it to compile, not just the first one.
You should add help.o to your g++ line:
g++ -c help.cpp -o help.o
g++ help.o main.cpp
By splitting it to two lines you can save compilation time (in case of larger projects), because you can compile help.cpp only when it was changed. make and Makefile used well will save you a lot of headache:
#Makefile
all: main
main: help main.cpp
g++ -o main help.o main.cpp
help: help.cpp
g++ -c -o help.o help.cpp
I had the same problem with my Linux Lubuntu distribution and it was creating the problem for my constructor and destructor. It was not recognizing them.
Actually, this goes off if you just compile all of the three files together. So, once you saved all your files, just do this:
g++ main.cpp Help.h Help.cpp
./a.out
./a.out is the executable file for the Linux. Sorry, but I don't know about the Windows. And your program would run smoothly.
I cannot get this simple piece of code to compile without including the TestClass.cpp file explicitly in my main.cpp file. What am I doing wrong? Thanks in advance!
Here is the code:
TestClass.h
#ifndef TESTCLASS_H_
#define TESTCLASS_H_
class TestClass
{
public:
static int foo();
};
#endif
TestClass.cpp
#include "TestClass.h"
int TestClass::foo() { return 42; }
main.cpp
#include <iostream>
#include "TestClass.h"
using namespace std;
int main()
{
cout << TestClass::foo() << endl;
return 0;
}
Here is the error:
g++ main.cpp -o main.app
/tmp/ccCjOhpy.o: In function `main':
main.cpp:(.text+0x18e): undefined reference to `TestClass::foo()'
collect2: ld returned 1 exit status
Include TestClass.cpp into the commandline, so the linker can find the function definition:
g++ main.cpp TestClass.cpp -o main.app
Alternatively, compile each to their own object file, then tell the compiler to link them together (it will forward them to the linker)
g++ -c main.cpp -o main.o
g++ -c TestClass.cpp -o TestClass.o
g++ main.o TestClass.o -o main.app
You're not compiling and linking against TestClass.cpp (where the implementation of foo() is). The compiler is thus complaining that your trying to use an undefined function.