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.
Related
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 have 3 files; main.cpp (which contains main()), FileWriter.h, and FileWriter.cpp. I'm using g++ (version Debian 4.9.2-10) on Debian Jessie. My project contains .cpp files in '/root/dev/Practice/src/', and a single header (FileWriter.h) in '/root/dev/Practice/include/'. The compilation of the two object files works, but the linking to an executable complains about undefined reference to main(), although I do indeed have a seemingly valid one defined in 'main.cpp'.
Here's the output of my make file (which is in the root '/root/dev/Practice/' directory):
g++ -c -g -Wall -o src/FileWriter.o src/FileWriter.cpp
g++ -c -g -Wall -o src/main.o src/FileWriter.cpp
g++ src/FileWriter.o src/main.o -o bin/Practice
/usr/lib/gcc/i586-linux-gnu/4.9/../../../i386-linux-gnu/crt1.o: In function '_start'"
/build/glibc-J1NNmk/glibc-2.19/csu/../sysdeps/i386/start.S:111: undefined reference to 'main'
collect2: error: ls returned 1 exit status
Makefile:10: recipe for target 'bin/Practice' failed
Here's the contents of my main.cpp file:
#include <string>
#include <iostream>
#include "/root/dev/Practice/include/FileWriter.h"
int main() {
std::cout << "Hello!" << std::endl;
FileWriter * fw = new FileWriter("foofile");
fw->AddLine("CRAP!");
fw->AddLine("NO!");
return 0;
}
My FileWriter.h:
#ifndef FILEWRITER_H_
#define FILEWRITER_H_
#include <string>
#include <iostream>
class FileWriter{
public:
FileWriter(std::string);
~FileWriter();
void AddLine(std::string);
private:
std::string fileLocation;
std::ofstream *filestream;
};
#endif /* FILEWRITER_H_ */
...and my FileWriter.cpp:
#include "/root/dev/Practice/include/FileWriter.h"
#include <fstream>
// g++ linker error if 'inline' not included - why?
inline FileWriter::FileWriter(std::string fileName)
{
this->fileLocation = fileName;
const char * x = this->fileLocation.c_str();
this->filestream = new std::ofstream();
this->filestream->open(x, std::ios::out | std::ios::app);
}
inline FileWriter::~FileWriter()
{
this->filestream->close();
}
inline void FileWriter::AddLine(std::string line)
{
*this->filestream << line << std::endl;
}
This line:
g++ -c -g -Wall -o src/main.o src/FileWriter.cpp
should be:
g++ -c -g -Wall -o src/main.o src/main.cpp
I don't have access to this compiler, but in the past if you had main() in a C++ file you needed to "decorate" it with __cdecl
int __cdecl main() {
Try that? Or:
extern "C" int main() {
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 made a program to test my knowledge on class but I had some troubles.
foo.h:
#include <iostream>
using namespace std;
class foo
{
private:
int a;
public:
foo();
};
foo.cc:
#include <iostream>
#include "foo.h"
using namespace std;
foo::foo()
{
a = 0;
}
And main.cc:
#include<iostream>
#include "foo.h"
int main()
{
foo a;
return 0;
}
I compiled this with g++ main.cc -o main. Then I got
-bash-4.1$ g++ main.cc -o main
/tmp/cc5Hnes8.o: In function `main':
main.cc:(.text+0x10): undefined reference to `foo::foo()'
collect2: ld returned 1 exit status
I think there should be a really stupid mistake here but I really cannot find it. I've been struggling on this whole night...
Appreciate any help!
You are asking the compiler to not only translate main.cc but also perform the final link to produce the executable main. This second step cannot be done because main.cc references the function foo::foo whose definition is in foo.cc and therefore not available to the compiler. You can do this:
g++ main.cc -c -o main.o
g++ foo.cc -c -o foo.o
g++ main.o foo.o -o main
The -c flag makes the compiler perform translation only, so this separately compiles main.cc and foo.cc and then links the objects together to obtain the executable. In this way, the definition of foo::foo will end up inside foo.o and will be available at link time.
Or, you can just provide both .cc files. This basically does the same thing as the three commands above:
g++ main.cc foo.cc -o main
You should compile all source (.cc in your case) files:
g++ main.cc foo.cc -o main
When you realize the constructor of foo in foo.cc， you should compile it.
use g++ main.cc foo.cc -o main.
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