I write simple testing program in C++, which will tell Hello, Alex and exit.
Here it's code:
main.cpp:
#include <iostream>
#include <dlfcn.h>
int main()
{
void* descriptor = dlopen("dll.so", RTLD_LAZY);
std::string (*fun)(const std::string name) = (std::string (*)(const std::string)) dlsym(descriptor, "sayHello");
std::cout << fun("Alex") << std::endl;
dlclose(descriptor);
return 0;
}
dll.h:
#ifndef UNTITLED_DLL_H
#define UNTITLED_DLL_H
#include <string>
std::string sayHello(const std::string name);
#endif
dll.cpp:
#include "dll.h"
std::string sayHello(const std::string name)
{
return ("Hello, " + name);
}
makefile:
build_all : main dll.so
main : main.cpp
$(CXX) -c main.cpp
$(CXX) -o main main.o -ldl
dll.so : dll.h dll.cpp
$(CXX) -c dll.cpp
$(CXX) -shared -o dll dll.o
But when I build my code with make, I have such error:
/usr/bin/ld: dll.o: relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; recompile with -fPIC
dll.o: error adding symbols: Bad value
collect2: error: ld returned 1 exit status
makefile:8: recipe for target 'dll.so' failed
make: *** [dll.so] Error 1
What did I make not correct?
P.S. I use GNU Make 3.81 on Ubuntu Server 14.04.3 with GNU GCC 4.8.4
Update
If I link dll.so file with -fPIC param, I have the same error
Firstly, a bit off topic, but in your makefile, it would be better to specify build_all as a phony target
.PHONY: build_all
Next, you are compiling dll.cpp without relocatable code. You need to add -fpic or -fPIC (see here for an explanation of the difference).
$(CXX) -c dll.cpp -fpic
Lastly, unix doesn't automatically add file suffixes, so here you need to specify .so:
$(CXX) -shared -o dll.so dll.o
Related
I tried to compile my c++ class with sqltie3 include.
I run Ubuntu 20.04.
For this I use the i686-w64-mingw32-g++ cross compiler, I also tested it with g++ and it works perfectly but not with the i686-w64-mingw32-g++ compiler.
I always get the same error:
/usr/bin/i686-w64-mingw32-ld: DBWrapper.o:DBWrapper.cpp:(.text+0x61): undefined reference to `sqlite3_open'
/usr/bin/i686-w64-mingw32-ld: DBWrapper.o:DBWrapper.cpp:(.text+0x12c): undefined reference to `sqlite3_close'
My Makefile:
mingw = i686-w64-mingw32-g++
SQLCOMPILE = -I/usr/local/sqlite/include
CFLAGS = -Wall
SRCFILES = *.cpp
OBJFILES = *.o
TARGETWIN = progwx.exe
all: $(TARGETWIN)
$(TARGETWIN): $(OBJFILES)
$(mingw) $(CFLAGS) $(OBJFILES) $(SQLCOMPILE) -o $(TARGET) -l sqlite3
$(OBJFILES): $(SRCFILES)
$(mingw) $(CFLAGS) $(SQLCOMPILE) -c $(SRCFILES)
.PHONY: clean
clean:
rm -f *.o
I put the sqlite source code in $(SQLCOMPILE) and the compiler can include everything unless I call the sqlite3_open() function.
I also compiled the source code to a library (libsqlite3.a) so that the -l tag can find it.
Because the g++ compiler brings also the same "undefined reference" error if I don't put the -lsqlite3 tag in.
$ i686-w64-mingw32-gcc -c sqlite3.c
$ ar rcs libsqlite3.a sqlite3.o
Here is my Headerfile (DBWrapper.h):
#pragma once
#include <string>
#include <stdexcept>
#include <sqlite3.h>
class DBWrapper {
sqlite3 *db_;
const int errCode;
public:
DBWrapper(const std::string &dbname);
DBWrapper(const DBWrapper&) = delete;
DBWrapper& operator=(const DBWrapper&) = delete;
sqlite3* operator*();
~DBWrapper();
};
Here is my CPP-File (DBWrapper.cpp):
#include "DBWrapper.h"
DBWrapper::DBWrapper(const std::string &dbname) : db_(nullptr), errCode(sqlite3_open(dbname.c_str(), &db_)){
if(errCode) {
throw std::runtime_error("ERROR at opening database!");
}
}
DBWrapper::~DBWrapper() {
sqlite3_close(db_);
}
sqlite3* DBWrapper::operator *() {
return db_;
}
(sorry for my bad english)
I figured it out I just needed sqlite3 as a compiled object file (sqlite3.o) for the compiler.
I created my Makefile for a simple program but it returns undefined reference for class functions constantly:
g++ -c src/main.cpp -o lib/main.o
g++ -c src/functions.cpp -o lib/functions.o
g++ -c src/Circular.cpp -o lib/Circular.o
g++ lib/main.o -o bin/app.exe
c:/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../../mingw32/bin/ld.exe: lib/main.o:main.cpp:(.text+0x20): undefined reference to `Circular::Circular()'
collect2.exe: error: ld returned 1 exit status
make.exe: *** [app.exe] Error 1
Here is my Makefile:
app.exe: lib/main.o lib/Circular.o lib/functions.o
g++ lib/main.o -o bin/app.exe
lib/functions.o: src/functions.cpp
g++ -c src/functions.cpp -o lib/functions.o
lib/Circular.o: src/Circular.cpp
g++ -c src/Circular.cpp -o lib/Circular.o
lib/main.o: src/main.cpp
g++ -c src/main.cpp -o lib/main.o
Here is a short snippet of main.cpp:
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <fstream>
#include <string>
#include "../include/Circular.h"
#include "../include/functions.h"
using namespace std;
int main(int argc, const char * argv[]) {
Circular item;
return 0;
}
Circular.h:
#include "node.h"
class Circular
{
public:
Circular();
node *start;
node *last;
int counter;
}
Circular.cpp:
#include "../include/Circular.h"
#include <iostream>
using namespace std;
Circular::Circular()
{
start = NULL;
last = NULL;
}
and node.h:
struct node
{
int data;
struct node *next;
struct node *prev;
};
I know the problem is about linker and with Makefile but even though I tried different possible solutions, somehow it doesn't work. Therefore, maybe someone can see the mistake I am making. Thanks!
I managed to create a Makefile from this source .
The Makefile looks like this:
CXX = g++
CXXFLAGS = -std=c++17 -Wall
LXXFLAGS = -std=c++17
OBJECTS = main.o Circular.o functions.o
TARGET = main
$(TARGET): $(OBJECTS)
$(CXX) $(LXXFLAG) $(OBJECTS) -o $(TARGET)
main.o: main.cpp Circular.cpp Circular.h functions.cpp functions.h
$(CXX) $(CXXFLAGS) -c main.cpp
Circular.o: Circular.cpp
$(CXX) $(CXXFLAGS) -c Circular.cpp
functions.o: functions.cpp
$(CXX) $(CXXFLAGS) -c functions.cpp
clean:
rm -f $(TARGET) $(OBJECTS)
And also added cout to you Circular constructor to check the execution as below:
#include "Circular.h"
#include <iostream>
using namespace std;
Circular::Circular()
{
start = NULL;
last = NULL;
cout << "Yes!" << endl;
}
Here's the result:
Output
Don't forget to put a semicolon for your Circular class in your Circular.h.
NOTE: If you aren't able to use make in cmd,use choco install make.
The Makefile should be structured to build the dependencies, then the final assembly into a .exe. Each path should be specified exactly as it is, not approximated:
app.exe: lib/main.o lib/Circular.o lib/functions.o
g++ lib/main.o lib/Circular.o lib/functions.o -o app.exe
lib/main.o: src/main.cpp
g++ -c src/main.cpp -o lib/main.o
lib/functions.o: src/functions.cpp
g++ -c src/functions.cpp -o lib/functions.o
lib/Circular.o: src/Circular.cpp
g++ -c src/Circular.cpp -o lib/Circular.o
The key here is be consistent and that includes things like the order of things specified in this file. Whatever order you pick, stick to it. This makes tracking down problems way easier.
If this project gets more complex you probably want to pivot to using a dependency tracking Makefile template instead of this homebrew one. Note how in those you don't need to specify a rule for each file, but instead a rule for each type of file, as in .cpp -> .o, and the rest happens automatically.
I need to access a C++ function from C but I get some error like :-
/tmp/ccUqcSZT.o: In function `main':
main.c:(.text+0x5): undefined reference to `load_alert_to_db'
collect2: error: ld returned 1 exit status
My main.c code is:-
#include <stdio.h>
extern void load_alert_to_db(void);
int main(void){
/* Create empty queue */
load_alert_to_db();
return 0;
}
C++ code implementation db_manager.cpp is:-
#include <sstream>
#include <iostream>
#include <sstream>
#include <string>
#include <ctime>
#include <cstdlib>
#include <algorithm>
#include <time.h>
#include <cstring>
#include <fstream>
//using namespace oracle::occi;
#include <iostream>
using namespace std;
extern "C" void load_alert_to_db(void)
{
cout<<"db occi"<<endl;
}
makefile is:-
CC= g++
all:
$(CC) -c -Wall -Werror -fPIC db_manager.cpp
$(CC) -shared -o libdb_manager.so db_manager.o
gcc -L/home/oracle/Desktop/storage/ -Wall main.c -o data -ldb_manager
gcc -o data main.c
clean:
rm -f *.o data
so please help me which one is my problem. I am also include
export LD_LIBRARY_PATH=/home/oracle/Desktop/storage/:$LD_LIBRARY_PATH
environmental variable in .bash_profile
gcc -o data main.c
Not sure why you have this line in your makefile since it will compile main.c without reference to the previously created library and hence cause an undefined-symbol error such as the one you're seeing.
This is especially so, since you appear to have done it the right way on the preceding line:
gcc -L/home/oracle/Desktop/storage/ -Wall main.c -o data -ldb_manager
However, the entire point of using makefiles is so that it figures out the minimum necessary commands for you, based on dependencies. Lumping a large swathe of commands into a single rule tends to defeat that purpose. You would be better off making your rules a little more targeted, such as (untested but should be close):
all: data
data: main.o libdb_manager.so
gcc -o data main.o -ldb_manager
main.o: main.c
gcc -o main.o main.c
libdb_manager.so: db_manager.cpp
g++ -c -Wall -Werror -fPIC -o db_manager.o db_manager.cpp
g++ -shared -o libdb_manager.so db_manager.o
That way, if you make a small change to one part (like main.c), it doesn't have to go and compile/link everything in your build tree.
Your makefile seems to be completely broken and random, and you're not even linking the required object files. You can simplify this:
all:
$(CC) -c -Wall -Werror -fPIC db_manager.cpp
$(CC) -shared -o libdb_manager.so db_manager.o
gcc -L/home/oracle/Desktop/storage/ -Wall main.c -o data -ldb_manager
gcc -o data main.c
to just this:
all:
gcc -Wall -c main.c
g++ -Wall -c db_manager.cpp
g++ main.o db_manager.o -o data
this is what I needed to do:
Supposing the C++ function is called Debug::Write(str)
Then in your hpp file do the following:
#ifdef __cplusplus
extern "C" void DebugTmp(char *str);
#endif
Then in the corresponding cpp file do this:
void DebugTmp(char *str)
{
Debug::Write(str);
}
Then in your C file where you call DebugTmp define the prototype:
void DebugTmp(char *str);
then call it as below:
static void MyFunction( void )
{
DebugTmp("This is debug trace\n");
}
I have no clue why boost::filesystem::copy_file is making trouble for me.
undefined reference to `boost::filesystem::detail::copy_file
// g++ -std=c++11 test.cpp -lboost_filesystem -lboost_system -lrt -lboost_wave
#include <boost/filesystem.hpp>
int main()
{
boost::filesystem::create_directory("aaa");
// ok
boost::filesystem::copy_file("f1","f2");
// /tmp/ccNWZltB.o: In function `boost::filesystem::copy_file(boost::filesystem::path const&, boost::filesystem::path const&)':
// test.cpp:(.text._ZN5boost10filesystem9copy_fileERKNS0_4pathES3_[_ZN5boost10filesystem9copy_fileERKNS0_4pathES3_]+0x26): undefined reference to `boost::filesystem::detail::copy_file(boost::filesystem::path const&, boost::filesystem::path const&, boost::filesystem::copy_option, boost::system::error_code*)'
// collect2: error: ld returned 1 exit status
return 0;
}
I got no inspiration from the source code of boost or its help:
inline
void copy_file(const path& from, const path& to, // See ticket #2925
BOOST_SCOPED_ENUM(copy_option) option, system::error_code& ec)
{detail::copy_file(from, to, option, &ec);}
Even such a simple example does not work for me.
Platform: Linux Ubuntu 64
There is a workaround for this problem, replace
#include <boost/filesystem.hpp>
with
#define BOOST_NO_CXX11_SCOPED_ENUMS
#include <boost/filesystem.hpp>
#undef BOOST_NO_CXX11_SCOPED_ENUMS
Or, preferably, add -DBOOST_NO_CXX11_SCOPED_ENUMS to your compiler flags
If you run into this problem make sure to include both -lboost_system and -lboost_filesystem in your call to g++
Example working Makefile
BINARY = output
FILE_OBJECTS = main.o fileLoader.o
BOOST = -lboost_system -lboost_filesystem
GCC = g++ -std=c++17
FLAGS = -Wall -pedantic -Wextra
build: $(FILE_OBJECTS)
$(GCC) $(FLAGS) $(FILE_OBJECTS) -o $(BINARY) $(BOOST)
main.o: main.cpp fileLoader.o
$(GCC) $(FLAGS) -c main.cpp
fileLoader.o: fileLoader.cpp
$(GCC) $(FLAGS) -c fileLoader.cpp
clean:
rm -rf *.o $(BINARY)
Example working code
#include <boost/filesystem.hpp>
void create_data_file(std::string file_path)
{
boost::filesystem::path p(file_path);
boost::filesystem::create_directory(p);
}
I could not compile a file that included the header boost/filesystem.hpp either. This is how I solved it: I commented out the line boost/filesystem.hpp and all the lines that were using Boost, and then compiled the file. I then uncommented all the lines in the files and compiled again, and then it worked. I was compiling with the flag -lboost_system both times!
In older boost versions it is BOOST_NO_SCOPED_ENUMS, not BOOST_NO_CXX11_SCOPED_ENUMS
see boost::filesystem::copy_file() missing symbol in c++11
lib.h:
#include <iostream>
namespace lib {
template <class T>
void f(T t)
{
std::cout << "lib f " << t << std::endl;
}
}
client.cpp:
#include "lib.h"
// explicit instantiation
template
void lib::f(char);
int main()
{
lib::f('x');
}
libmock.h:
#include <iostream>
#include "lib.h"
namespace lib {
template <>
void f(char c)
{
std::cout << "libmock f " << c << std::endl;
}
}
Makefile:
run: prod test
./prod
./test
prod: client.o
${CXX} -o $# $^
test: client.o libmock.o
${CXX} -o $# $^
clean:
-rm *.o prod test
Using GCC 4.3.2 (and also "IBM XL C/C++ for AIX, V11.1 (5724-X13)"), I get the results that I expect:
$ make
g++ -c -o client.o client.cpp
g++ -o prod client.o
g++ -c -o libmock.o libmock.cpp
g++ -o test client.o libmock.o
./prod
lib f x
./test
libmock f x
That is, I've injected new functionality into the client by linking it with an object that provides a more-specialized function template than the one offered by the library.
However, if I use "CC: Sun C++ 5.12 SunOS_sparc Patch 148506-14 2013/09/24", then I get this error:
$ CXX=CC make
CC -c -o client.o client.cpp
CC -o prod client.o
CC -c -o libmock.o libmock.cpp
CC -o test client.o libmock.o
ld: fatal: symbol 'void lib::f<char>(__type_0)' is multiply-defined:
(file client.o type=FUNC; file libmock.o type=FUNC);
Makefile:9: recipe for target 'test' failed
make: *** [test] Error 2
My solution must work with all three of these compilers. Am I just getting lucky with some undefined behavior in GCC and AIX? Are there some options I could pass to the Sun compiler to get this to work? Does what I'm trying to do show that I'm not fully understanding these template concepts? Enlighten me, please!
Your test binary that links libmock.o and client.o together violates the one definition rule (in the client translation unit it uses the default version and in the libmock translation unit it uses the specialized version) and thus both linker behaviors are ok.
I will continue thinking about alternatives but right now the only solutiion I can think of is to conditionally include libmock.h in client.cpp based on whether you're doing the mock test build or not.