I picked up the following demo off the web from https://computing.llnl.gov/tutorials/pthreads/
#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5
void *PrintHello(void *threadid)
{
long tid;
tid = (long)threadid;
printf("Hello World! It's me, thread #%ld!\n", tid);
pthread_exit(NULL);
}
int main (int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc;
long t;
for(t=0; t<NUM_THREADS; t++){
printf("In main: creating thread %ld\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
pthread_exit(NULL);
}
But when I compile it on my machine (running Ubuntu Linux 9.04) I get the following error:
corey@ubuntu:~/demo$ gcc -o term term.c
term.c: In function ‘main’:
term.c:23: warning: incompatible implicit declaration of built-in function ‘exit’
/tmp/cc8BMzwx.o: In function `main':
term.c:(.text+0x82): undefined reference to `pthread_create'
collect2: ld returned 1 exit status
This doesn't make any sense to me, because the header includes pthread.h
, which should have the pthread_create
function. Any ideas what's going wrong?
This question is related to
c
linux
multithreading
pthreads
Both answers to this question so far are incorrect.
For Linux the correct command is:
gcc -pthread -o term term.c
In general, libraries should follow sources and objects on command line, and -lpthread
is not an "option", it's a library specification. On a system with only libpthread.a
installed,
gcc -lpthread ...
will fail to link.
I believe the proper way of adding pthread
in CMake
is with the following
find_package (Threads REQUIRED)
target_link_libraries(helloworld
${CMAKE_THREAD_LIBS_INIT}
)
you need only Add "pthread" in proprieties=>C/C++ build=>GCC C++ Linker=>Libraries=> top part "Libraries(-l)". thats it
Since none of the answers exactly covered my need (using MSVS Code), I add here my experience with this IDE and CMAKE build tools too.
Step 1: Make sure in your .cpp, (or .hpp if needed) you have included:
#include <functional>
Step 2 For MSVSCode IDE users: Add this line to your c_cpp_properties.json file:
"compilerArgs": ["-pthread"],
Step 2 For CMAKE build tools users: Add this line to your CMakeLists.txt
set(CMAKE_CXX_FLAGS "-pthread")
Note: Adding flag -lpthread (instead of -pthread) results in failed linking.
Compile it like this : gcc demo.c -o demo -pthread
For Linux the correct command is:
gcc -o term term.c -lpthread
Sometimes, if you use multiple library, check the library dependency. (e.g. -lpthread -lSDL... <==> ... -lSDL -lpthread)
If you are using cmake, you can use:
add_compile_options(-pthread)
Or
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
In Anjuta, go to the Build menu, then Configure Project. In the Configure Options box, add:
LDFLAGS='-lpthread'
Hope it'll help somebody too...
in eclipse
properties->c/c++Build->setting->GCC C++ linker->libraries in top part add "pthread"
You need to use the option -lpthread
with gcc.
In Visual Studio 2019 specify -pthread
in the property pages for the project under:
Linker -> Command Line -> Additional Options
Type in -pthread
in the textbox.
check man page and you will get.
Compile and link with -pthread.
SYNOPSIS
#include <pthread.h>
int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg);
Compile and link with -pthread.
....
Acutally, it gives several examples of compile commands used for pthreads codes are listed in the table below, if you continue reading the following tutorial:
Running from the Linux terminal, what worked for me was compiling using the following command (suppose the c file I want to compile is called test.c):
gcc -o test test.c -pthread
Hope it helps somebody!
Source: Stackoverflow.com