即使我包含正确的头文件，为什么还会出现“未定义的引用”错误？

When I tried to compile this program, it failed:

当我尝试编译这个程序时，它失败了：

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>

void *WriteNumbers(void *threadArg)
{
    int start, stop;

    start = atoi((char *)threadArg);
    stop = start + 10;

    while (start < stop)
    {
         printf("%d\n", start++);
         sleep(1);
    }
    return 0;
}

int main(int argc, char **argv)
{
        pthread_t thread1, thread2;

        // create the threads and start the printing
        pthread_create(&thread1, NULL, WriteNumbers, (void *)argv[1] );
        pthread_create(&thread2, NULL, WriteNumbers, (void *)argv[2]);

        pthread_join(thread1, NULL);
        pthread_join(thread2, NULL);

        return 0;
}

It gave me the following errors:

它给了我以下错误：

tmp/ccrW21s7.o: In function `main':
pthread.c:(.text+0x83): undefined reference to `pthread_create'
pthread.c:(.text+0xaa): undefined reference to `pthread_create'
pthread.c:(.text+0xbd): undefined reference to `pthread_join'
pthread.c:(.text+0xd0): undefined reference to `pthread_join'
collect2: ld returned 1 exit status

Why does it give me these undefined reference errors even though I had included pthread.h, which declares these functions?

为什么它给了我这些未定义的引用错误，即使我已经包含pthread.h，它声明了这些函数？

4 个解决方案

#1

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

您可能忘记链接Pthreads库（在命令行上使用-lpthread）。

#2

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:

其他人提到你没有使用-lpthread标志与pthread库链接。现代GCC（不确定现代，我的4.3.3）允许你只使用-pthread。从手册页：

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

-pthread使用pthreads库添加对多线程的支持。此选项为预处理器和链接器设置标志。

#3

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

您需要将pthread库链接到二进制文件，如下所示：

cc -o myapp myapp.c -lpthread

#4

做

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

to compile the program, then

然后编译程序

./name

to run the program.

运行程序。

#1