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...
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
I've created a source file that contains a number of data structures (maps, vector, array). Its header file is #included in the main-file.
The main file looks like this:
#include "reachability.h" //Where monkey() and vector<int> int_req are declared
main()
{
monkey(int_req); // Calling monkey(int_req) here is OK! Bar is visible
...
ifstream fp("foo.txt");
if(fp.is_open())
{
std::string line;
while( getline(fp,line) )
{
monkey(int_req); //'int_req' is an undefined reference!
}
}
}
And reachability.h
#ifndef REACHABILITY_H
#define REACHABILITY_H
extern std::vector<int> int_req;
void monkey(std::vector<int> feces);
#endif
And reachability.cc
std::vector<int> int_req;
void monkey(std::vector<int> thrown_obj)
{
... //Iteration and dereferencing of "thrown_obj"
}
I've accessed data structures that are declared in reachability.cc in a for-loop in the scope of main and that was fine. Something wonky is happening in this if-statement though.
Compiler Error:
lab1.o: In function `main':
/home/ubuntu/workspace/ECE597/Lab1/lab1.cc:105: undefined reference to `int_req'
collect2: error: ld returned 1 exit status
Edited: reachability.cc is included in compiliation:
elusivetau:~/XXXX/XXXX/XXXX $ g++ lab1.cc parser.cc gate.cc reachability.cc -o run
/tmp/ccJK4O9q.o: In function `main':
lab1.cc:(.text+0x489): undefined reference to `int_req'
collect2: error: ld returned 1 exit status
Edited: makefile for this program:
all: lab1.o parser.o gate.o reachability.o
g++ -g lab1.o parser.o gate.o reachability.o -o run
lab1.o: lab1.cc
g++ -g -c lab1.cc
parser.o: parser.cc
g++ -g -c parser.cc
gate.o: gate.cc
g++ -g -c gate.cc
reachability.o: reachability.cc
g++ -g -c reachability.cc
clean:
rm *o run
Whatever it is, you're not giving us the correct information.
I added includes and removed non-code to make this compile. And voila, it also links:
test.cpp:
#include "reachability.h" //Where monkey() and vector<int> int_req are declared
#include <string>
#include <iostream>
#include <fstream>
main()
{
monkey(int_req); // Calling monkey(int_req) here is OK! Bar is visible
std::ifstream fp("foo.txt");
if(fp.is_open())
{
std::string line;
while( getline(fp,line) )
{
monkey(int_req); //'int_req' is an undefined reference!
}
}
}
reachability.h:
#ifndef REACHABILITY_H
#define REACHABILITY_H
#include <vector>
extern std::vector<int> int_req;
void monkey(std::vector<int> feces);
#endif
reachability.cpp:
#include "reachability.h"
std::vector<int> int_req;
void monkey(std::vector<int> thrown_obj)
{
}
This compiles and links just fine. You are leading us on a wild goose chase by not bothering to create a mvce
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.
This question already has answers here:
creating classes link error
(2 answers)
Closed 8 years ago.
I'm trying to learn how to make classes in C++ where I use a header file, a .cpp file that contains the class function definitions, and a main .cpp file. Here is what I have (taken from an example)
in class.h
class MyClass
{
public:
void foo();
int bar;
};
in class.cpp
#include "class.h"
using namespace std;
void MyClass::foo()
{
cout<< "test";
}
in main.cpp
#include "class.h"
using namespace std;
int main()
{
MyClass a;
a.foo();
return 0;
}
Compiling the main.cpp results in this error:
[Linker error] C:\:(.text+0x16): undefined reference to `MyClass::foo()'
collect2: ld returned 1 exit status
Do I need to compile the class.cpp or class.h? Am I missing a way of linking class.h with class.cpp? If so how do I link them?
You need to compile the implementation files into object files and link them together. The following is an example for when you are using g++:
g++ -c class.cpp -o class.o
g++ -c main.cpp -o main.o
g++ class.o main.o -o main
./main
In reality, you would add more options like -std=c++11 -O3 -Wall -Wextra -Werror etc.
You can try this on Linux shell using g++
Compile Create object files of main.cpp and class.cpp called main.o and class.o
g++ -c class.cpp
g++ -c main.cpp
Linking the object codes main.o and class.o to create executable file called program
g++ -o program main.o class.o
then run the program executable file
./program
You are likely to be compiling only main.cpp and not class.cpp.
What command are you using to generate the output ?
This should work fine :
g++ class.cpp main.cpp -o class
Its working fine
I tried the code in my Compiler
MyClass.h
#include <iostream>
class MyClass
{
public:
void foo();
int bar;
};
MyClass.cpp
#include "MyClass.h"
using namespace std;
void MyClass::foo()
{
cout<< "test";
}
Main.cpp
#include <iostream>
#include "MyClass.h"
int main(int argc, const char * argv[])
{
MyClass a;
a.foo();
return 0;
}
Ive tried the code in Xcode.
Its working just fine.
Use compiler option -I<dir of .h file> while compiling .cpp file. Compile both the .cpp files
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.