I know there are several questions like this, no answer I have found so far seems to solve my problem.
I am using eclipse.
I coded something in the main function, and it worked fine.
I then an external function with the code in the main and now I get funny mistakes.
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <random>
#include <ctime>
#include <cstdlib>
using namespace std;
using namespace cv;
void createSaltandPepper();
int main(int argc, char** argv) {
createSaltandPepper();
return 0;
}
No, as I am trying not to give to extensive an example again, here is the outside of the function:
void createSaltandPepper() {
//mycode
}
At least it does not seem to be a spelling mistake.
However, the error is:
make all
make: *** No rule to make target 'SaltPepper.o', needed by 'Display'.
I do wonder why it is trying to make a tagert called SaltPepper.o if my function is called createSaltandPepper.
Can somebody help me?
Edit: I did not conciously create a makefile, as I said I am working with eclipse.
And again, the code works fine as long as it is inside the main function instead of inside createSaltandPepper().
My file is called DisplayImage.cpp, the code above is in this file, including the function createSaltandPepper();
The only two function in this file are the main function and createSaltandPepper();
There are no other source files in the project.
I am sorry if I come across as rather stupid: I am a Java programmer and have not a clue about makefiles and such.
See this screenshot:
I now created a new project and added my old file into it, this time calling it Display.cpp
"build all" resulted in an error in subdir.mk which reads:
subdir.mk:18: recipe for target 'Display.o' failed
make: *** [Display.o] Error 1
The complete Error message for the build is as follows:
make all
Building file: ../Display.cpp
Invoking: GCC C++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0-std=c++11 -MMD -MP -MF"Display.d" -MT"Display.d" -o"Display.o" "../Display.cpp"
subdir.mk:18: recipe for target 'Display.o' failed
g++: error: argument to ‘-fmessage-length=’ should be a non-negative integer
make: *** [Display.o] Error 1
Update
I switched to Netbeans.
It now works.
First, this error has nothing to do with compilers, this error message is produced by the build system (make in your case). Basically, eclipse seems to call make, which figures out what are dependencies between files and which of them need recompiling and in turn calls the compiler to compile them. Every C++ source file is then compiled to an object file .o (typically with the same name: SaltPepper.cpp -> SaltPepper.o). Then all the object files are linked together with the libraries to form the final executable.
This particular error message tells you that your executable is specified to depend on the object file SaltPepper.o, but the build system does not know how to produce it. Most likely there is no corresponding SaltPepper.cpp file. So check if such file exists. If not, check the settings of your project (or the Makefile if you created it manually) and see if all the cpp filenames are specified correctly. You should add all the cpp files with your code to the project, and remove all the extraneous cpp files.
Update: Note that build system operates on the file level. It does not know anything about functions etc., only source files. Maybe this is the source of the confusion.
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'm learning SDL2 right now and I'm working in XCode for the most part as I code. However, I want to run my program in terminal to use valgrind, but whenever I try, I get this error:
fatal error: 'SDL2/SDL.h' file not found
I'm compiling in a really simple way as follows:
g++ Camera.cpp LTexture.cpp LTimer.cpp LWindow.cpp Player.cpp Tile.cpp TileMap.cpp main.cpp -o main
I know that I'm supposed to be including the SDL2 library somehow, but I'm unsure of how to do that. Right now, the framework is sitting in the folder /Library/Frameworks/SDL2.framework
Any help on this would be greatly appreciated. Thanks in advance.
Add
-I/Library/Frameworks/SDL2.frameworks/Headers
to your g++ command and change
'SDL2/SDL.h'
include to just
'SDL.h'
in your header/(s) since /Library/Frameworks/SDL2.frameworks/Headers doesn't contain an SDL2 folder (usually)
Now that you changed the #include "SDL2/SDL.h" to #include "SDL.h" you want to go open your Xcode project, select your target, go to build settings and add /Library/Frameworks/SDL2.frameworks/Headers to Header Search Paths in order to fix Xcode's 'Couldn't find 'SDL.h'' error message.
Update:
Another way would be linking (using ln) /Library/Frameworks/SDL2.frameworks/Headers to /usr/local/include/SDL2, add -I/usr/local/include/SDL2 to your g++ command
and leave the #include as is ('SDL2/SDL.h')
this will probably a dumb question for you guy's but I have no experience in C++ what so ever. I'm using an open source project osrm (which is awesome). Still to request a route, you have make an http request. To reduce the running time, I would like to build a wrapper around the code and call it using the command line. So I googled a bit and found that osrm already creates a static lib (.a file) when compiling the project. I also found a piece of code that points me in the right directions for building a wrapper. So to begin I build a simple hello world program (see below) that includes some files from that static lib. To compile I followed this tutorial.
My directory structure looks like this:
./helloWorld.cpp
./libs/libOSRM.a
And the command to compile is this:
gcc –static helloworld.cpp –L ./libs –l libOSRM.a
The code it selve:
#include "Router.h"
#include "boost/filesystem/path.hpp"
#include "ServerPaths.h"
#include "ProgramOptions.h"
#include <InternalDataFacade.h>
#include <viaroute.hpp>
#include <iostream.h>
main()
{
cout << "Hello World!";
return 0;
}
the exact error I got:
fatal error: ServerPaths.h: No such file or directory #include "ServerPaths.h"
Add the -IPathToTheHeaderFiles to the compiler options. So it will find the files to be included. Replace PathToTheHeaderFiles with the path where your file ServPaths.h resides.
Edit: Add as many -I as you need for further header files.
Additionally it would be worth to read a book about C++ or/and the GCC manual1
1 Section 3.11 will help.
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.