Home/ Questions/''Undefined reference to pthread create'' - How to solve it?
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martinakertzmann
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Asked: 2022-06-15T01:09:46+00:00 In:

”Undefined reference to pthread create” – How to solve it?

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Hey, guys! I’m back here. I have a trouble with the error: ”undefined reference to pthread create” while I am running this program:

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);
}

Then I get an error:

[email protected]:~/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

I don’t know where is wrong and how to fix it. Please help me.

undefined reference to pthread create
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1 Answer

  1. Best Answer
    Expert

    The cause:

    After looking over your program, I found that while you were compiling a C program with GCC on Linux, and you used the wrong compilation command. You only set up:

    gcc -lpthread ...

     -lpthread is a library specification, not an option. Therefore, the error happened. Solution: You must use pthread flag, so let’s change to this correct command for Linux:

    add_compile_options(-pthread)

    When you add pthread to your IDE’s linker libraries, you will no longer get pthread reference errors. Navigate to libraries in Eclipse by using the following sequences: Properties > C/C++ Build > Setting > GCC C++ linker > libraries. Add pthread once you’ve arrived. However, if you can’t find the C/C++ Build option, you can use the CMakeLists.txt file in Eclipse as a solution. Before the add executable command, add the following to the CMakeLists.txt file:

    SET(CMAKE_EXE_LINKER_FLAGS “${CMAKE_EXE_LINKER_FLAGS} -pthread”)

    This will allow Eclipse to support CMake pthreads. It will also tell the linker the way to do the same. Another way is using the -pthread argument in add compile options like follows:

    add_compile_options(-pthread)

    If you follow above suggestions, you will eliminate ”Undefined reference to pthread_create” error.

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