This is a tutorial I've been following and I've done everything that it tells but it doesn't work. I have three files: the main.cpp, burrito.h (the class), and burrito.cpp.
And here are the three files respectively.
main.cpp
#include <iostream>
#include "Burrito.h"
using namespace std;
int main() {
Burrito bo;
return 0;
}
Burrito.h
#ifndef BURRITO_H
#define BURRITO_H
class Burrito {
public:
Burrito();
};
#endif // BURRITO_H
Burrito.cpp
#include <iostream>
#include "Burrito.h"
using namespace std;
Burrito::Burrito() {
cout << "Hello World" << endl;
}
When I build and run I get the following error:
...undefined reference to `Burrito::Burrito()'
collect2: ld returned 1 exit status
Process terminated with status 1 (0 minutes, 6 seconds)
1 errors, 0 warnings
I'm compiling using CodeBlocks.
I'm using CodeBlocks
This is the issue.
If you’re starting to learn C++ it’s (unfortunately) essential to learn about translation units. An IDE like Code::Blocks hides this detail from you – and does it wrong, in this case (this isn’t really the fault of Code::Blocks though, it can’t automatically guess what to do in this case without configuation).
In the beginning, drop the IDE, go to the command line for compiling. Compile the two translation units separately and link them together explicitly.
g++ -o burrito.o burrito.cpp
g++ -o main.o main.cpp
g++ -o main main.o burrito.o
Every good beginners’ C++ book will explain how this works.
When you're linking objects together to get the final executable file you're forgetting to link the compiled-object from burrito.cpp file correctly
If you're building with a Makefile, your final output rule should have something like "-o main main.o burrito.o"
Using Code Blocks 13.12 I right clicked on the Burritto.cpp file chose Properties, then chose the Build tab and checked the compile file and link file check boxes then clicked ok saved everything then ran and it worked great.
Related
I am trying to write a C++ class in a separate header and cpp file using VS Code as my IDE with the 'run' and 'C++' extensions.
main.cpp
#include "Fan.h"
int main() {
Fan fan1;
return 0;
}
Fan.h
#ifndef FAN_H
#define FAN_H
class Fan {
public:
Fan();
};
#endif
Fan.cpp
#include "Fan.h"
#include <iostream>
using namespace std;
Fan::Fan() {
cout << "Fan Class" << endl;
}
I really can't seem to find anything popping out as obviously wrong. I am wondering if it is a setup problem with VS Code.
If I change #include "Fan.h" in main.cpp to "Fan.cpp" it works so it makes me think that the code works but that the linker is not setup right.
Would appreciate any help!
EDIT: Ok so I've tried the code in a different IDE and it worked. It's something to do with VS Code. Here is the error:
[Running] cd "c:\Users\<USER>\Desktop\Fan\" && g++ tempCodeRunnerFile.cpp -o tempCodeRunnerFile && "c:\Users\<USER>\Desktop\Fan\"tempCodeRunnerFile
C:\Users\<USER>\AppData\Local\Temp\cclMFKxO.o:tempCodeRunnerFile.cpp:(.text+0x57): undefined reference to `Fan::Fan()'
collect2.exe: error: ld returned 1 exit status
It sounds like the IDE is only compiling main.cpp. You need to find the command that is compiling main.cpp and ensure that it also compiles fan.cpp into fan.obj. You will also need to ensure that both main.obj and fan.obj are passed to the linker (which produces the executable program, main.exe or whatever).
There are two steps involved here:
cpp -> obj (compiling each source file into a matching object file)
obj -> exe (linking many object files into an executable)
I would say to make a CMakeLists.txt file and add main.cpp and fan.cpp into the add_executable section. Then VS can handle and run files through CMake.
I am just learning c++ and began to watch a youtube tutorial by thenewboston. Unfortunately he is using Code::Blocks while I am using gcc and I do not have the option to create new class files with a button click and so had to manually create them.
I dont understand why the same code in Code::Blocks and gcc will work in Code::Blocks but not gcc. Does gcc require different coding for the same language?
EDIT: I have downloaded and tested in Code::Blocks myself
Other questions talk of how I need to give windows an entry point, but I dont know how to do that.
Test.cpp Code:
#include <iostream>
#include "ClassTest.h"
using namespace std;
int main() {
ClassTest bo;
}
ClassTest.h Code:
#ifndef CLASSTEST_H
#define CLASSTEST_H
class ClassTest {
public:
ClassTest();
};
#endif // CLASSTEST_H
ClassTest.cpp Code:
#include <iostream>
#include "ClassTest.h"
using namespace std;
ClassTest::ClassTest() {
cout << "blah blah" << endl;
}
I'm not quite sure I understand what the question is; I'm going to take it as "how do I get these three files to build into a .exe that I can run from the Windows commmand line?"
The answer is to run something like this on the command line, in the folder with the files:
g++ -c Test.cpp -o Test.o
g++ -c ClassTest.cpp -o ClassTest.o
g++ Test.o ClassTest.o -o Test.exe
The first two commands build each CPP file into an "object file", which isn't a whole program by itself but which contains the compiled version of the code in that CPP file. The last command tells the compiler to paste together the two object files into a program, and resolve all the cross-references between them. (For example, the part where Test.cpp constructs a ClassTest object needs to end up calling the ClassTest constructor code from ClassTest.cpp.)
Code::Blocks is an IDE and works out how to build each source file in your project and link them together by itself. But if you aren't using an IDE, you need to do that in another way. You can either do it manually like this, or you can write a Makefile that will check which code files have changed and rebuild and re-link everything that depends on them when you run the make command, which is how most people do it.
As for "giving Windows an entry point", that probably refers to GUI applications that want to display windows on the screen. For console programs like the one you have written, the "entry point" is main(), and you just print stuff to the command line window. To make actual Windows-style GUI windows of your own, you need to use the Windows API, which I can't tell you much about.
main.cpp
#include <iostream>
#include <string>
using namespace std;
void echo(string);
int main()
{
echo("hello");
cout << "Hello world!" << endl;
return 0;
}
print.cpp
#include <iostream>
#include <string>
void echo(string code){
cout << code;
}
After compiling the code in code blocks 12.11, it gives me that error:
undefined reference to `echo(std::string)
I use windows 7 x64.
I have added the directory; Project>build options > search directories and added the current working directory.
All the files are in one console project in code blocks
I believe you should read up a bit more on namespaces usage. You are missing std in print.cpp.
Generally, while starting to learn cpp or getting a grip of the language you should always try writing full names of the classes along with the namespaces. Eventually with practice and some oversights (like now) you will learn why you really need them. In a nutshell namespaces are great:
When you are writing code over multiple files
Compartmentalize your code into separate blocks.
Also, using namespace std; should be used within cpp files mostly (otherwise headers get mangled up.
Anyways, try changing your code to this:
#include <iostream>
#include <string>
void echo(std::string code){
std::cout << code;
}
Then your results will look like this:
> g++ main.cpp print.cpp -o a.out
> ./a.out
helloHello world!
You should get more than that linker error, since you use string without any namespace in your print.cpp file. And if that source file doesn't compile it can't be linked with, and you will get the linker error you have.
Change to e.g.
void echo(std::string code) { ... }
And you do try to link with the object file created from print.cpp ?
I know this is old, but for anyone looking to solve this issue, the following may be a solution for you. If you have g++ follow c++ 11 under project->build options (check your options anyway) then you must check that box for all files you make in the project for the error to be cleared up. I had that annoying undefined reference thing too but now it is gone!
Try "Project/Properties/Build Targets tab". There you should find "Build target files" field. In that filed find "print.cpp" and click the checkbox (now the compiler will build print.cpp).
Some usefull information on Project management in CB
http://www.codeblocks.org/docs/main_codeblocks_en.html
When dealing with strings in C++ its best to sue std::string and your code seems to be wrong with a changes like using std::cout instead of plain cout another thing you need to be careful is linking your files especially files in different directories you need to tell code blocks were to find this print.cpp by going to build option and go for the search tab directory and point to where print.cpp is other wise the other approach is to just build a project which will have the main.cpp and and then add print.cpp class to current project I hope this will be of some help
I have two files:
hello.h and hello.cpp
hello.h
#ifndef __HELLO_H__
#define __HELLO_H__
using namespace std;
void PrintMessage();
#endif
hello.cpp
#include <iostream>
#include "hello.h"
using namespace std;
void PrintMessage()
{
cout << "I want to be displayed!";
}
Now, I want to use PrintMessage() in a new .cpp file, but I keep getting an error message. This is what I'm doing:
printingmessage.cpp
#include <iostream>
#include "hello.h"
using namespace std;
int main()
{
PrintMessage();
return 0;
}
Am I just doing something blatantly wrong? I do have all of them in the same folder; I assume it has something to do with Dev-C++ (what I'm using to write/compile/run), but I can't figure it out. Anyone have any ideas?
I created a folder on my desktop, put all three files inside, and I tried to compile my printingmessage.cpp file exactly as it is. This is the error I'm getting:
[Linker error] Undefined reference to 'PrintMessage()'
i don't know dev C++ , but i would strongly advise if you do any serious coding to learn/move to the terminal and use make files, or a newer IDE such as visual studios.
heres a short script you can run save it as bash.sh
something like this
g++ hello.cpp -O2 -g -c
g++ hello.o printmessage.cpp -Wall -O2 -o print
then run it with ./print
I assume it has something to do with Dev-C++ (what I'm using to
write/compile/run), but I can't figure it out.
I guess so, too. Behind the scenes, the following things have to happen:
Both files get compiled. This creates a *.obj file for every *.cpp file, and uses the header.
The object files are linked against one another and possibly against required libraries.
Your problem lies in the “one another” part of the second step: the code compiles all right, but linking fails. The header file is irrelevant at that point. More precisely, the linker invocation for printingmessage.obj contains a reference to a function which isn't defined in that object file or any of the default libraries. Most likely the problem is due to the *.cpp files not being part of the same project. You need to create a multi-source-file project where you can link multiple object files. How you do that with Dev-C++ is probably somewhere in their manuals.
I'm having a linking issue with a basic C++ program. No, I'm not including .cpp files!
This is what's happening.
main.cpp:
#include "header.h"
#include <iostream>
int main() {
std::cout << "Hello!";
}
header.h:
#ifndef _HEADER_H
#define _HEADER_H
class Something {
public:
printContents();
};
#endif
something.cpp:
#include "header.h"
#include <iostream>
Something::printContents() {
cout << "This class's Contents!!";
}
What's happening is that I get a compiler error going: multiple definitions of some standard C function, such as strtod:
g++ -o ... main.o
build/....main.o: In function
`strtod':
../MinGW/bin/../lib/gcc/mingw32/3.4.5/../../../../include/stdlib.h:318:
multiple definition of `strtod'
build/..something.o:...something.cpp:(.text+0x0):
first defined here collect2: ld
returned 1 exit status
If I get rid of #include <iostream> in one of the two occasions and get rid of the couts, it will compile. What's going on? I'm using g++ and NetBeans to compile.
I tried in the command line:
g++ *.h *.cpp -o program
and the same thing happened.
Please note that _HEADER_H is an illegal name in C++ user code - names beginning with the underscore and an uppercase letter are reserved for the C++ implementation. This does not normally cause noticeable problems, but when you use what may be a common name in the implementation like HEADER in this context, it well might.
Modify,
Something::printContents()
{
std::cout << "This class's Contents!!";
}
NOTE: Specify the return datatype.
One of your problems is right here:
I tried in the command line: g++ *.h
*.cpp -o program
Don't pass your header files... Try something like this:
g++ *.cpp -o program
I could not reproduce your exact problem. I get this to compile and link nicely with the following few notes:
Add a void return type to the printContents-function (So it says void printContents(); in the header and void Something::printContents() { in the implementation-file)
Use std::cout rather than just cout. cout is not defined in the scope it is used
Make sure header.h ends with a blank line
Use HEADER_H rather than _HEADER_H (like Neil Butterworth says)
I use the command line g++ main.cpp something.cpp to compile.
I see a couple of problems. You shuold define the returning value of the function
printContents()
and you must write
std::cout
if you don't write
using namespace std;
The problem was in a multi-installation of MinGW. I had one already installed, and when I got Qt on my computer, it had installed it's own MinGW. Bummer, I ported the code to my university's servers and it ran OK.
Bummer!!
Thanks everybody for the help, I will definitely follow your guidelines in the future.
Header names - no underscores
Correct return type
Real code in the forums!
Leo Bruzzaniti