For one reason or another, I am messing around with the exit() function in c++. I am getting all kinds of strange errors from my mac running lion (64 bit). I am compiling using g++ -o -g -Wall.
Exhibit A:
#include <iostream>
int main(int arc, char *argv[]){
exit(1);
}
The Terminal output looks like this
$ g++ -o -g -Wall test main.cpp
ld: in test, can't link with a main executable for architecture x86_64
collect2: ld returned 1 exit status
but $ g++ -o test main.cpp compiles fine.
using #include<stdio.h> or #include<stdlib.h> result in the same compilation error.
I am just wondering if anyone might be able to see immediately what is going on here?
test is the name of the binary to produce, your first argument list should be:
> g++ -g -Wall -o test main.cpp
^^^^^^^ -o has test for an argument
-o is meant to be followed immediately by the name of the output file. It is probably trying to use your old binary 'test' as a source file, incorrectly.
Try this:
g++ -o test -g -Wall main.cpp
Related
I am a very new to programming and have a very basic question that may be answered in other threads however I think they are far too advanced for me to understand how. I have actually found many answers so far on this site but this is the first problem that forced me to create an account and ask.
Anyway i am running a very basic example program on linux mint 18.3. Now I have seen this exact code work on a machine with windows 8 I believe so I was wondering if that could be the problem. I have created a class and when i plug in my object then build and run I get:
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o||In function _start':|
(.text+0x20)||undefined reference tomain'|
This is the entire code:
#include <iostream>
#include "Gladius.h"
using namespace std;
int main()
{
Gladius io;
return 0;
}
Thats it very basic. here is the .h
#ifndef GLADIUS_H
#define GLADIUS_H
class Gladius
{
public:
Gladius();
};
#endif // GLADIUS_H
and the .cpp for the class.
#include "Gladius.h"
#include <iostream>
using namespace std;
Gladius::Gladius()
{
cout << "The Gladius is a short sword" << endl;
}
I know this seems extremely simple but I am just learning to code and i have been looking all over for an explanation why this isn't working yet I see it work on another pc exactly as is. Anyway any explanation would be greatly appreciated.
Here is what i found in command line If this answers your questions about what was in the cmd.
g++ -Wall -fexceptions -g -std=c++11 -Wall -I -c /home/gator/Documents/Spartan1/Gladius.cpp -o obj/Debug/Gladius.o
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o: In function _start':
(.text+0x20): undefined reference tomain'
collect2: error: ld returned 1 exit status
Know the compiler options(gcc/g++ compiler):
-c : Compile and assemble, but do not link
-o file : Place the output into file
So when you run
g++ filename.cpp -o executable_name
, you generate an application which can be executed.
The problem is you are compiling, assembling as well as linking when you are trying to compile "Gladius.cpp" and compiler is trying to search for main() definition.
So in your case, the compilation steps would be:
First compile "Gladius.cpp" and generate object file "Gladius.o":
g++ -Wall -fexceptions -g -std=c++11 -c Gladius.cpp
Next compile "main.cpp" and generate object file "main.o":
g++ -Wall -fexceptions -g -std=c++11 -c main.cpp
Generate executable by linking "main.o" and "Gladius.o"
g++ -Wall -fexceptions -g -std=c++11 -o main main.o Gladius.o
Now you can run "main":
./main
Your compiler's command line contains -I -c sequence.
This -I option "swallows" your -c option. -I requires an additional argument, which is an include directory name. You failed to supply that argument, which is why -I assumes that -c that follows it is the directory name. So that -I consumes that -c.
The compiler never sees that -c. Without -c it assumes that you want to compile and link your program. Since Gladius.cpp does not have main in it, you get the error at linking stage.
Here 's a simple demo of the same problem: http://coliru.stacked-crooked.com/a/8a37cd3e90a443e2
You need to figure out why you have an orphaned -I in your command line.
If you are compiling this code using a command line like:
g++ -Wall -Wextra -Werror -O gladius.cpp -o output.exe
then make sure that you include all the .cpp files (not .h files) that contain code that your program needs.
g++ -Wall -Wextra -Werror -O gladius.cpp main.cpp -o output.exe
I explain this to beginners all the time as each .cpp being a bag of Lego's in a kit. You need all the bags that came with the box in order to build the kit. If you omitted main.cpp (or the file that contains main) then you will get the linker error that you are currently getting.
What command are you using to compile, link, and then execute? It should look something like
$ g++ main.cpp gladius.cpp -odemo
$ ./demo
check your command line for linking step.. You may forgot file with main as input, or you had forgot output file name after -o (and masked main.o in result)
I had this very kind of problem myself, and though it may not be the conventional, "proper" solution, I simply renamed the ".c" file to ".cpp", and it all worked.
After all, I was compiling both c and c++ together with a c++ compiler (recommended by the library), and the c code already had the proper c++ #extern flags (see here for more on that).
Also related:
C++ Error: undefined reference to `main'
Including C Code in C++
Why do you need an explicit `-lm` compiler option
Compilation on Linux - In function '_start': (.text+0x20): undefined reference to 'main'
I'm trying to make a C++ script that will run some simple Python code:
// t.cpp
#include <Python.h>
int main(int argc, char* argv[])
{
Py_Initialize();
PyRun_SimpleString("print('TEST PASSED')");
Py_Finalize();
return 0;
}
Upon running g++ t.cpp, I get the error:
t.cpp:1:20: fatal error: Python.h: No such file or directory
compilation terminated
I've found many similar questions, all specific to an IDE or other development software, or were solved by installing python3-dev. The python3-dev package is already installed, and I even tried manually including the header when attempting to compile:
g++ t.cpp -I ~/.virtualenvs/MainEnv/include/python3.5m/Python.h
g++ t.cpp -I /usr/include/python3.5m/Python.h
Neither changes anything.
How can I fix this error?
UPDATE: I found that using g++ t.cpp -I /usr/include/python3.5/ seems to include the header, but then it runs into more errors:
t.cpp:(.text+0x10): undefined reference to `Py_Initialize'
t.cpp:(.text+0x1f): undefined reference to `PyRun_SimpleStringFlags'
t.cpp:(.text+0x24): undefined reference to `Py_Finalize'
collect2: error: ld returned 1 exit status
I've set up a similar example on my github
g++ t.cpp is missing a few things:
Tell g++ where the headers are for cpython (by -I/path/to/headers/)
Tell g++ to link against libpython (by -lpython3.5m)
You can also retrieve these flags with pkg-config
$ pkg-config python-3.5 --libs --cflags
-I/usr/include/python3.5m -I/usr/include/x86_64-linux-gnu/python3.5m -lpython3.5m
Your commandline should look something like g++ -I/usr/include/python3.5m t.cpp -lpython3.5m
#include <...> is for includes that come with the compiler.
Use #include "Python.h" for any other includes.
Run the following commands to compile your code:
mytest.cpp:
#include <Python.h>
int main(int argc, char* argv[])
{
Py_Initialize();
PyRun_SimpleString("print('TEST PASSED')");
Py_Finalize();
return 0;
}
Compile:
$ g++ mytest.cpp `pkg-config python3-embed --libs --cflags` -o mytest
$ ./mytest
I am using Netbeans for my C++ project. I compiled my program using make and ran into this error:
collect2: error: ld terminated with signal 11 [Segmentation fault], core dumped
Makefile:4: recipe for target 'barn' failed
make: *** [barn] Error 1
Whereas, when I compiled it in a linux environment(Ubuntu to be precise), it compiled fine. What could have possibly gone wrong?
This is what I got when I typed make -n:
g++ -c main.cc
g++ -c Animal.cc
g++ -c Bird.cc
g++ -c Chicken.cc
g++ -c Cat.cc
g++ -c Pig.cc
g++ -o barn main.o Animal.o Bird.o Chicken.o Cat.o Pig.o Random.o
PS I prefer using Netbeans
A segment fault in the linker suggests a bug with that. This is what I would try if I were to run into this problem.
At the command line do
g++ -o barn main.cc Animal.cc Bird.cc Chicken.cc Cat.cc Pig.cc Random.cc
If that does not work, try variations like:
g++ -o barn main.cc Pig.cc Random.cc Animal.cc Bird.cc Chicken.cc Cat.cc
The order should not matter. This is just the kind of thing I would try with a mystery-meat problem like this.
Yes this question has been asked before ... I've tried everything mentioned in the previous answers. My setup is really straightforward so this shouldn't be so hard.
I just want to program against mysql using C++. My source code is taken verbatem from the 'hello world' type example here:
http://dev.mysql.com/doc/refman/5.1/en/connector-cpp-examples-complete-example-1.html
I am on Ubuntu 12.10. I am trying:
g++ -Wall -o firsttry_prog -I/usr/include/mysqlcppconn -I/usr/local/boost_1_53_0 -L/usr/lib/x86_64-linux-gnu -l:libmysqlclient_r.so.18 -L/usr/lib/mysqlcppconn -lmysqlcppconn firsttry.cpp
It compiles (if I use -c option) but won't build, giving me the infamous:
/tmp/ccn768hj.o: In function `main':
firsttry.cpp:(.text+0x3a): undefined reference to `get_driver_instance'
A few details:
'firsttry.cpp' is just what I named the source code file, again taken verbatem from the official example
As you can see I AM linking in the mysqlclient library and the mysqlcppconn library. Many times when this question has been asked previously, the answer was to link those.
Some other historical answers suggest the sample source code is wrong and that the function in question needs to be in the sql::mysql namespace etc. I am pretty sure the source code is fine. Again, it compiles, and changing the namespaces in the source code just seems to make it worse.
Thank you in advance for any help you can provide.
So I have now had this problem for a week now and I became very frustrated with it as well. I just now was able to finally build a program that does nothing except login to mysql and I literally squealed with joy. Here is what I have and I hope it helps.
I first compiled the c++ connector library from source but after a while I thought maybe I did something wrong so I then just used apt to get it with:
sudo apt-get install libmysqlcppconn-dev
And here is my simple tester source file "tester.cpp"
#include <stdlib.h>
#include <iostream>
#include <mysql_connection.h>
#include <driver.h>
#include <exception.h>
#include <resultset.h>
#include <statement.h>
using namespace sql;
int main(void){
sql::Driver *driver;
sql::Connection *con;
driver = get_driver_instance();
con = driver->connect("tcp://127.0.0.1:3306","root","YOURPASSWORD");
return 0;
}
And finally g++ compile command:
g++ -Wall -I/usr/include/cppconn -o testapp tester.cpp -L/usr/lib -lmysqlcppconn
This worked for me and I hope it helps you solve your problem!
For me simply swapping the order of the last two arguments fixed this problem. I don't know why but the linker is able to find the function get_driver_instance if I specify the -lmysqlcppconn option at the end after the source file.
g++ -Wall -o firsttry_prog -I/usr/include/mysqlcppconn -L/usr/lib/mysqlcppconn firsttry.cpp -lmysqlcppconn
Also note that I took out the following options as I think they are redundant
-I/usr/local/boost_1_53_0 -L/usr/lib/x86_64-linux-gnu -l:libmysqlclient_r.so.18
In case you are as forgetful as me and didn't link the library in CMakeLists.txt:
target_link_libraries(<target> mysqlcppconn)
If all the paths are included throw param -I. You would see whether there is a problem if you compile like this:
g++ -g -o0 -I/usr/local/include -I/usr/local/boost/include -c main.cpp -o main.o
g++ -g -o0 -L/usr/local/lib -L/usr/local/mysql/lib -lmysqlcppconn main.o -o test
the problem will appear:
main.o: In function `main':
/home/huangxw/workspace/public/soal/test/main.cpp:165: undefined reference to `get_driver_instance'
collect2: ld returned 1 exit status
Now you must adjust the order of -lmysqlcppconn and main.o:
g++ -g -o0 -I/usr/local/include -I/usr/local/boost/include -c main.cpp -o main.o
g++ -g -o0 -L/usr/local/lib -L/usr/local/mysql/lib main.o -o test -lmysqlcppconn
That is all!!
The reason is simple. You can find out using the web or ask me to elaborate.
Why this does not work, file test.c:
#include <event.h>
int main(void)
{
event_init();
return 0;
}
Then:
gcc -o test.o -c test.c runs OK, but
Link:
g++ -o test -levent test.o produces
test.o: In function `main':
test.c:(.text+0x5): undefined reference to `event_init'
collect2: ld returned 1 exit status
So it cannot be linked as C++. How to solve this? I need to link it as C++ and compile as C.
This question has been asked many times. On Linux, you should put libraries after object and source files in the compilation command. So try
g++ -Wall -g -c mytest.cc
g++ -Wall -g mytest.o -levent -o mytest
Avoid calling your test program test which is an existing utility or shell builtin.
As a newbie, remember to always compile with all warnings asked -Wall and for debugging -g and learn to use gdb