即使使用lpthread也有未定义的对“ pthread_join”错误的引用

Question

I am using linux on ubuntu. However, I am having problem even using pthread and lpthread. Please help! Thank you in advance!

yuki@ubuntu:~/NetBeansProjects/csci212A3$ g++ Path.o Maze.o SubmitMazeSoln.o TestSubmitMazeSoln.cpp -o -lpthread
In file included from Maze.h:12:0,
             from TestSubmitMazeSoln.cpp:11:
Assignm3_Utils.h: In constructor ‘Point::Point()’:
Assignm3_Utils.h:17:19: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null]
Point ()    { x = NULL; y = NULL; }
               ^
Assignm3_Utils.h:17:29: warning: converting to non-pointer type ‘int’ from NULL [-Wconversion-null]
Point ()    { x = NULL; y = NULL; }
                         ^
/tmp/ccMQbyoO.o: In function `newThread()':
TestSubmitMazeSoln.cpp:(.text+0x3ab2): undefined reference to `pthread_create'
TestSubmitMazeSoln.cpp:(.text+0x3b0a): undefined reference to `pthread_create'
TestSubmitMazeSoln.cpp:(.text+0x3b53): undefined reference to `pthread_join'
TestSubmitMazeSoln.cpp:(.text+0x3b79): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status

Answer 1

Is this really an accurate copy of your command line:

g++ Path.o Maze.o SubmitMazeSoln.o TestSubmitMazeSoln.cpp -o -lpthread

The -o option specifies the output file, and expects an argument. As written above, this argument is -lpthread . So -lpthread is not an argument (and the pthread library will not be searched); it is the name of your output file. (And you don't really want an executable, or any file, with the name -lpthread ; filenames which start with a - cause no end of problems under Unix.)

With regards to the warnings: I would guess from them that x and y in Point have type int . NULL is the conventional way of specifying a null pointer, and using it as an int is obfuscation in the first degree. So g++ warns. (Of course, from C++11 on, one should prefer nullptr for a null pointer, rather than NULL .)