I've installed boost, so i'm trying to run compiler like this:g++ -LC:\MinGW\boost_1_55_0\stage\lib -lboost_regex-mgw49-mt-1_55 test.cpp
My programm test.cpp is not very complicated:
#include <iostream>
int main()
{
std::cout << "Hello, world!" << std::endl;
boost::regex rex("[test]");
}
I'm of course failed: error: 'boost' has not been declared. I can't understand what I must write in my test.cpp file next to #include <iostream>? #include <boost> doesn't work, i'm getting error fatal error: boost: No such file or directory.
#include <boost/regex.hpp> also yield this error, maybe #include <boost_regex-mgw49-mt-1_55>? But it still doesn't work.
You need to include regex.hpp in your main. You hint that you tried to, but it apparently didn't work.
Make sure regex.hpp is where you tell the compiler it is relative to one of your search directories. It's not good enough to tell the compiler to include boost/regex.hpp, the file has to actually exist where the compiler is looking for it to be able to find it.
You will need to copy that file from wherever you downloaded it to somewhere the compiler will know to look for it. Once you do that, it should find it and that error should go away.
Also note that the same applies to the object file you're trying to link in. If the linker can't find that file, you'll just get a linker error once you clear up this compiler error.
Related
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.
In my makefile on this project, I am specifying 3 location for the compiler to find #includes.
INCLUDES=-I. -I/home/kelly/xerces/xerces-c-3.1.1/src -I/home/kelly/Utilities_New
When I compile the following sample code with the command line found in the comment:
#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
#include <xercesc/util/XMLString.hpp>
using namespace std;
/*
g++ -I. -I/home/kelly/xerces/xerces-c-3.1.1/src -I/home/kelly/Utilities_New test.cpp
*/
int main(int argc, char* argv[])
{
cout << "this works" << endl;
}
In file included from /home/kelly/Utilities_New/string.h:5:0,
from /home/kelly/xerces/xerces-c-3.1.1/src/xercesc/framework/XMLBuffer.hpp:28,
from /home/kelly/xerces/xerces-c-3.1.1/src/xercesc/util/XMLString.hpp:26,
from test.cpp:7:
/home/kelly/Utilities_New/defs.h:26:21: fatal error: windows.h: No such file or directory
compilation terminated.
Clearly the compiler has decided that when it processes the Xerces #includes and finds string.h in the Utilities_New directory, it has found what it needs and stops there.
This other string.h was written by another programmer and I am attempting to use his library.
I thought that the standard locations were searched first. I'm a little lost here. I may be missing something super obvious to you all.
Also, wasn't there some rule about #include files that had <> vs. "" around them and where the compiler was supposed to look?
The standard locations are searched last.
#include "blah" is identical to #include <blah> unless blah is found in the same directory as the file that tries to include it. (And unless you use the rare and gcc-specific -iquote option).
For more information see here.
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