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Undefined reference to pthread_create [FIXED]

C++

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In this article, we have explored the reason behind the error "Undefined reference to pthread_create" and presented two fixes in the compilation command to fix this compilation error.

Table of contents:

  1. Reason for the error
  2. Fix 1: pthread
  3. Fix 2: lpthread

In short, the fix is to use pthread flag in compilation:

gcc -pthread -o code code.c

Reason for the error

While compiling a C code using the function pthread_create(), you may face this compilation error:

code.c: In function β€˜main’:
/tmp/cc8BMzwx.o: In function `main':
term.c:(.text+0x82): undefined reference to `pthread_create'
collect2: ld returned 1 exit status

This issue can come when you are not linking the pthread library during compilation.

Following is a sample C code where pthread_create is used and where the compilation error will be faced:

#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS  64

void *run(void * id)
{
   // ... Do computation
   pthread_exit(NULL);
}

int main (int argc, char *argv[])
{
   pthread_t threads[NUM_THREADS];
   for(iter=0; iter < NUM_THREADS; ++iter){
      pthread_create(&threads[t], NULL, run, (void *)iter);
   }
   pthread_exit(NULL);
}

Error if you compile using the command:

gcc -o code code.c

We will explore 2 fixes.

Fix 1: pthread

pthread option is used to add multi-threading support in C code with pthread library. It links both preprocessor and linker.

gcc -pthread -o code code.c

Fix 2: lpthread

Another fix is to add lpthread option to the compilation command. It adds pthread library in the linker. Depending on your system, this may fix the error while -pthread option is a complete solution.

gcc -o code code.c -lpthread

With these fixes in this article at OpenGenus, you must have the complete idea of how to fix this compilation error "Undefined reference to pthread_create".

Geoffrey Ziskovin

Geoffrey Ziskovin

Geoffrey Ziskovin is an American Software Developer and Author with an experience of over 30 years. He started his career with Haskell and has interviewed over 700 candidates for Fortune 500 companies

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OpenGenus Foundation OpenGenus Foundation
Undefined reference to pthread_create [FIXED]
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