I have made a c++ project in CodeBlocks. Now I started using Visual Studio Code and I can't figure out how to connect files. I have main.cpp with my main code, then I have sortlib.cpp with some sorting functions and I have sortlib.h. My question is how do I connect these files, so I can #include "sortlib.h" in my main.cpp file and use the functions.
I have tried including sortlib.h in my sortlib.cpp program and then my sortlib.h in my main.cpp program, but it didn't work.
I'm on windows so I just compiled my sortlib.cpp program by typing g++ sortlib.cpp and it showed me this error message
c:/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../../mingw32/bin/ld.exe: c:/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../libmingw32.a(main.o):(.text.startup+0xc0): undefined reference to 'WinMain#16'
Minimal code structure
main.cpp
// Other header files
#include "sortlib.h"
int main(void) {
...
}
sortlib.h
void someFunction();
...
sortlib.cpp
// Include headers that are required
void someFunction() {
...
}
The minimal required command
g++ -g main.cpp sortlib.cpp
There is no such thing as "connecting" files in programming. You have to make sure that your compiler is compiling all the .cpp files into .o/.obj files and that they are all getting linked together to produce your final executable.
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.
Trying to create dll.
So first I created a .java file as follows:
class Main
{
static
{
System.loadLibrary("sample_dll");
}
static native void sritest();
public static void main(String [] a)
{
sritest();
}
}
Then I compile it with no error to .class.
Then using javah I created Main.h.
Then I write following code in c++.
#include <jni.h>
#include <Main.h>
JNIEXPORT void JNICALL Java_Main_sritest(JNIEnv *env,jobject obj)
{
printf("hi");
}
Then I compiled this using MinGw by the following code
g++ -c sample_dll.cpp
g++ -shared -o sample_dll.dll sample_dll.o
Then I place this in java library path.
Then I run Main.java but the following exception occurs
Unstatisfied link error; sritest ()V
I find an answer . It is i do three mistakes. When compiling with c++ we must declare my jni function in extern "C"{} block. Second when compiling in minGW compiler we should use following code and implement include folder of jdk . The code now worked and my program runs smoothly without problem in jni.
The command line code for compiling .o to .dll code is after creating sample_dll.o we must do
g++ -Wall -D_JNI_IMPLEMENTATION -Wl,--kill-at -Ic:/path_of_include_folder_in_jdk_without_drive_letter -Ic:/path_of_win32_folder_in_include_folder_in_jdk_without_drive_letter -shared -o sample_dll.dll sample_dll.o
The last mistake is i want to include Main.h compiled by javah utlity that created from my java code.
This is done by
Javac Main.java
Javah Main
Then take the header file Main.h created and place it in the c++ compiler's include folder. That in my computer c:\minGW\include .
In c++ code add additional preprocessor
#include<Main.h>
All done create dll and place it in one of default java library path . The paths can be getted by using the following function in java
System.out.println (System.getProperty ("java.library.path"));
I'm trying to call C code from C++. I have 3 files: pubsub.cpp, pubsublib.c & pubsublib.h.
I know I have to use extern "C" in order to call a C function from C++.
I've literally tried everything, but I am still getting the following LNK2019 unresolved external symbol error:
LNK2019 unresolved external symbol _thisIsATestFunction referenced in
function _main
pubsublib.c
#include "pubsublib.h"
void thisIsATestFunction()
{
// do something
}
pubsublib.h
#ifndef pubsublib_H
#define pubsublib_H
void thisIsATestFunction();
#endif
pubsub.cpp
#include <string>
#include <iostream>
#ifdef __cplusplus
extern "C"{
#endif
#include "pubsublib.h"
#ifdef __cplusplus
}
#endif
using namespace std;
int main() {
thisIsATestFunction();
return 0;
}
I have also tried to just include the functions but I'm getting the same error. I'm really lost at the moment and have searched a lot... Any help would be greatly appreciated.
It works perfectly fine when you actually link with the necessary file.
When you compile pubsub.cpp you have to add pubsublib.obj to the command line. For example, this solved the problem for me using Visual Studio 2015:
cl -c pubsublib.c
cl pubsub.cpp pubsublib.obj
If you're building with the IDE, you simply need to make sure that pubsublib.c is a dependency and pubsublib.obj is specified as input to the link step.
You have to add a reference to the library in your application.
If you have both projects in one solution in Visual C++ 2015 you
right click your application project
select "Add..." from the drop down menu
select "Reference" from the menu
check you library in the list
If you have each project in its own solution you
right click you application project
select "Properties"
open "Linker" section "Input" page
add your .lib file to the "additional dependencies"
Your application should compile without LNK2019 after doing so.
There are also "build dependencies" to manage, but these do not affect the libraries linked to your project (only the build order).
(I am using a german edition of Visual Studio so please fix the translations if some of them are wrong)
Your declaration works fine, as proves the error message (_thisIsATestFunction is indeed a C-undecorated name).
Now two possibilities remain
the file pubsublib.c was not compiled as C, causing the compiled function to get decorated;
the file pubsublib.c was compiled as C, but didn't take part to the linking.
Only your solution/project(s) file can tell the truth. Can we see a screen copy of the Solution Explorer ?
This linkage error is produced when "pubsublib.c" file is compiled as C++ file (in g++). Please change your project options so that all .cpp files are compiled with g++, and all .c files are compiled with gcc.
After changing settings make sure that "pubsublib.c" file is really compiled with gcc. It can be found in compilation output like following:
g++.exe -c main.cpp -o main.o
gcc.exe -c pubsublib.c -o pubsublib.o
g++.exe main.o pubsublib.o -o Project1.exe
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.