Why do I get “undefined reference” errors even when I include the right header files?

Question

When I tried to compile this program, it failed:

#include 
#include 
#include 
#include 

voi         


        

Answer 1

Do

gcc -pthread -o name filename.c (cpp)

to compile the program, then

./name

to run the program.

Answer 2

You need to link pthread library to your binary, like this:

cc -o myapp myapp.c -lpthread

Answer 3

You probably forgot to link with the Pthreads library (using -lpthread on the command line).

Answer 4

For folks looking for the csapp solution. Compile "csapp.c" first, then

gcc -o filename filename.c csapp.o -lpthread

Answer 5

Others have mentioned that you haven't linked with the pthread library using the -lpthread flag. Modern GCC (not sure how modern, mine is 4.3.3) allows you to use just -pthread. From the man page:

-pthread
Adds support for multithreading with the pthreads library. This option sets flags for both the preprocessor and linker.