this is my code:
#include <boost/thread.hpp>
#include <iostream>
using namespace boost;
void task1()
{std::cout << "This is task1!" << std::endl;}
void task2()
{std::cout << "This is task2!" << std::endl;}
int main ()
{
thread thread_1 = thread(task1);
thread thread_2 = thread(task2);
thread_2.join();
thread_1.join();
return 0;
}
and I compile with:
g++ test.cc -o test -lboost_thread -lpthread -lboost_system
compile failed:
/tmp/ccN9cPiI.o: In function `boost::system::generic_category()':test.cc(.text._ZN5boost6system16generic_categoryEv[_ZN5boost6system16generic_categoryEv]+0x7):
undefined reference to `boost::system::detail::generic_category_instance'
collect2: error: ld returned 1 exit status
What's wrong with that?
My system is Ubuntu 18.04,boost is 1_68.0.
I just tried your example and it works. I tried with boost_1_66_0 and boost_1_65_1 on Ubuntu.
The actual problem is boost itself, not your installation. You can check open bug here:
https://github.com/boostorg/system/issues/24
Related
I am trying to compile & link a simple C++ program using threads on an aarch64 based linux host. The simple program is as follows:
#include <iostream>
#include <thread>
#include <atomic>
using namespace std;
#define ITERATIONS 1000
// to be called for multi threaded execution
void increment_atomic_thread (atomic<int>& a)
{
for (int i = 0; i < ITERATIONS; i++)
{
a++;
}
}
int main (int argc, char* argv[])
{
atomic<int> a, b, c, d;
thread t1 ( [&]() { increment_atomic_thread(a); } );
thread t2 ( [&]() { increment_atomic_thread(b); } );
thread t3 ( [&]() { increment_atomic_thread(c); } );
thread t4 ( [&]() { increment_atomic_thread(d); } );
t1.join();
t2.join();
t3.join();
t4.join();
return 0;
}
This code compile fine on an x86-64 machine, however I am getting an ld error in the aarch64 machine as follows (the output is last few lines when compiling with --verbose):
attempt to open /usr/lib/gcc/aarch64-linux-gnu/7/../../../aarch64-linux-gnu/crtn.o succeeded
/usr/lib/gcc/aarch64-linux-gnu/7/../../../aarch64-linux-gnu/crtn.o
libm.so.6 needed by /usr/lib/gcc/aarch64-linux-gnu/7/libstdc++.so
found libm.so at /usr/lib/gcc/aarch64-linux-gnu/7/../../../aarch64-linux-gnu/libm.so
/usr/bin/ld: /usr/lib/aarch64-linux-gnu/libpthread.a(pthread_create.o): relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol `__stack_chk_guard##GLIBC_2.17' which may bind externally can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: /usr/lib/aarch64-linux-gnu/libpthread.a(pthread_create.o)(.text+0x9cc): unresolvable R_AARCH64_ADR_PREL_PG_HI21 relocation against symbol `__stack_chk_guard##GLIBC_2.17'
/usr/bin/ld: final link failed: Bad value
collect2: error: ld returned 1 exit status
The compile command is:
g++ -g -std=c++17 -lpthread -Xlinker --verbose -o pthread_basic.app pthread_basic.cpp /usr/lib/aarch64-linux-gnu/libpthread.a
Thanks #Some programmer dude. Pasting his comment here:
You don't need both -lpthread and /usr/lib/aarch64-linux-gnu/libpthread.a. Remove
the last and keep -lpthread but put it at the end of the command line (order matters for libraries).
I am trying to use a vector of threads. I will receive an int as a parameter, which will be the number of threads I will have to create.
I tried something like this:
#include <iostream>
#include <thread>
#include <vector>
void credo()
{
std::cout << "threads" << std::endl;
}
void threads_creation()
{
int i;
std::vector<std::thread> threads_tab;
i = 0;
while(i < 2)
{
threads_tab.push_back(std::thread(credo));
i++;
}
}
int main()
{
threads_creation();
return (0);
}
But I get this compilation error:
/tmp/ccouS4PY.o: In function `std::thread::thread<void (&)()>(void (&)())':
threads.cpp:(.text._ZNSt6threadC2IRFvvEJEEEOT_DpOT0_[_ZNSt6threadC5IRFvvEJEEEOT_DpOT0_]+0x21): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
by compiling using the following command:
g++ -W -Wall -Werror -Wextra threads.cpp
What's wrong here?
The std::thread class utilizes pthreads in Linux, so you need to add the -pthread compiler flag to your command;
g++ -W -Wall -Werror -Wextra -pthread threads.cpp
I have some troubles trying to compile a program with multi-threading from the standard template library.
It return me a obscure error when i try to compile the following program :
#include <iostream>
#include <thread>
void foo()
{
std::cout << "Thread 1\n";
}
int main(int argc, char** argv)
{
std::thread tr(foo);
std::cout << "Main thread\n";
tr.join();
return 0;
}
I don't understand the error :
/tmp/ccE8EtL1.o : In the function « std::thread::thread<void (&)()>(void (&)()) » :
file.cpp:(.text._ZNSt6threadC2IRFvvEJEEEOT_DpOT0_[_ZNSt6threadC5IRFvvEJEEEOT_DpOT0_]+0x21) : undefined reference to « pthread_create »
collect2: error : ld has return 1 execution status code
I compile it with :
g++ -std=c++14 file.cpp -o test -Wall
Can anyone help me please ?
Pass -pthread to the compiler. This flag combines what is necessary to compile and link the pthread library (-lpthread is not always enough). See this question.
This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 7 years ago.
I am having a problem calling functions from my test_dll.dll in an outside c++ main. Working on eclipse cdt luna sr2 64, Windows 7. Using the MinGW toolchain for compilation.
The dll .cpp code :
#include <iostream>
#include "MyClass.h"
namespace myNamespace {
MyClass::MyClass() :a(1) {
std::cout << "MyClass():a(" << this->a << ")"<<std::endl;
}
MyClass::~MyClass() { }
void myFunc() {
std::cout << "myFunc() has been called !" << std::endl;
}
}
and it is compiled within eclipse with the following lines :
g++ -O0 -g3 -Wall -c -fmessage-length=0 -o MyClass.o "..\\MyClass.cpp"
g++ -shared -o libtest_dll.dll MyClass.o
My main code is the following :
#include <iostream>
#include "MyClass.h"
using namespace std;
int main() {
cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
myNamespace::MyClass *instance = new myNamespace::MyClass;
instance->myFunc();
return 0;
}
and it is compiled with the following
g++ "-IC:\\Users\\nxa02192\\Desktop\\MY_WORKSPACE\\test_dll" "-includeC:\\Users\\nxa02192\\Desktop\\MY_WORKSPACE\\test_dll\\MyClass.h" -O0 -g3 -Wall -c -fmessage-length=0 -o "src\\test_main.o" "..\\src\\test_main.cpp"
g++ "-LC:\\Users\\nxa02192\\Desktop\\MY_WORKSPACE\\test_dll\\Debug" -o test_main.exe "src\\test_main.o" -llibtest_dll
src\test_main.o: In function `main':
C:\Users\nxa02192\Desktop\MY_WORKSPACE\test_main\Debug/../src/test_main.cpp:20: undefined reference to `myNamespace::MyClass::myFunc()'
collect2.exe: error: ld returned 1 exit status
However, what i don't get is that if i just instanciate the class, it will output the correct a=1 value, as specified in the constructor.
I already specified the include paths to the compiler and the library path and file to the linker, as you can see in the compiling commands. Any Ideas ? Thanks !
Change
void myFunc() {
std::cout << "myFunc() has been called !" << std::endl;
}
to
void MyClass::myFunc() {
std::cout << "myFunc() has been called !" << std::endl;
}
omp.cpp
#include <iostream>
#include <omp.h>
int main() {
std::cout << "Start" << std::endl;
#pragma omp parallel
{
std::cout << "Hello ";
std::cout << "World! " << std::endl;
}
std::cout << "End" << std::endl;
}
I've tried to compile the above code with g++ omp.cpp -fopenmp but I get the error:
c:/mingw/bin/../lib/gcc/mingw32/4.8.1/../../../../mingw32/bin/ld.exe: cannot find -lpthread
collect2.exe: error: ld returned 1 exit status
I've tried googling what -lpthread is but I couldn't find anything. The closest thing I found was another thread in which someone compiled his/her code like this: g++ omp.cpp -fopenmp -lpthread ... but the result is the same for me.
Am I missing something? Much appreciated in advance.
pthread is the POSIX thread library.
-lpthread is a linker argument, meaning you are trying to link your binary with pthread.
The error means that this library is not available on your OS.
It looks like you are using mingw on Windows.
No surprise pthread isn't available on Windows, as it's a POSIX library.
But you may find some ways to have it on the MinGW website:
http://www.mingw.org/wiki/pthreads_library
Looks like you'll have to install a third-party library called pthreads-win32:
https://sourceware.org/pthreads-win32/