c - netfilter 队列 undefined reference `nfq_open'

Question

我已经写了这段代码:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <linux/types.h>
#include <linux/netfilter.h>
#include <libnetfilter_queue/libnetfilter_queue.h>
int main(int argc, char **argv)
{
    struct nfq_handle *h;
    printf("opening library handle\n");
    h = nfq_open();
    nfq_close(h);
    exit(0);
}

当我尝试编译时它说:

/tmp/ccEv9MYS.o: In function `main':
test1.c:(.text+0x1a): undefined reference to `nfq_open'
test1.c:(.text+0x2a): undefined reference to `nfq_close'
collect2: ld returned 1 exit status

我尝试检查该库是否被 gcc 找到并且它是(当我修改 libnetfilter_queue 的包含时出现错误)，我重新编译了该库并确认我正在调用的函数在其中。

如果你有任何线索，谢谢你的帮助

我用这个编译:

gcc -o test test1.c

我也试过:

gcc -o test -lnetfilter_queue test1.c
gcc -o test -L/usr/local/lib test1.c

Answer 1

嗯，来自 gcc manual page , 对于 -llibrary 链接选项

It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, ‘foo.o -lz bar.o’ searches library ‘z’ after file foo.o but before bar.o. If bar.o refers to functions in ‘z’, those functions may not be loaded.

也就是说，链接器从左到右工作，因此需要将依赖项放在左侧。

你需要把你的编译语句改成

 gcc -o test test1.c -lnetfilter_queue