Linux 即使 nm 指示此符号存在于共享库中，也未定义对符号的引用
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原文地址: http://stackoverflow.com/questions/10456581/
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undefined reference to symbol even when nm indicates that this symbol is present in the shared library
提问by user389238
What could be wrong here? I have the following simple class:
这里可能有什么问题？我有以下简单的类：
#include "libmnl/libmnl.h"
int main() {
struct mnl_socket *a = mnl_socket_open(12);
}
And after running a simple gcccompile (gcc -lmnl main.c) I get the following errors:
在运行一个简单的gcccompile ( gcc -lmnl main.c) 后，我收到以下错误：
/tmp/cch3GjuS.o: In function `main':
main.c:(.text+0xe): undefined reference to `mnl_socket_open'
collect2: ld returned 1 exit status
Running nm on the shared library shows that it's actually found:
在共享库上运行 nm 显示它确实找到了：
aatteka@aatteka-Dell1:/tmp$ nm -D /usr/lib/libmnl.so | grep mnl_socket_open
0000000000001810 T mnl_socket_open
This is happening on Ubuntu 12.04. The libmnl-devand libmnl0packages are installed. The straceoutput of gccindicates that ldis using exactly that *.so file:
这发生在 Ubuntu 12.04 上。该libmnl-dev的和libmnl0包安装。的strace输出gcc表明ld正在使用该 *.so 文件：
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.so", 0x7fff2a39b470) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.so", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.a", 0x7fff2a39b4d0) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/libmnl.a", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.so", 0x7fff2a39b470) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.so", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.a", 0x7fff2a39b4d0) = -1 ENOENT (No such file or directory)
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libmnl.a", O_RDONLY) = -1 ENOENT (No such file or directory)
[pid 10988] stat("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libmnl.so", {st_mode=S_IFREG|0644, st_size=18608, ...}) = 0
[pid 10988] open("/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../lib/libmnl.so", O_RDONLY) = 7
采纳答案by geekosaur
Libraries must be listed after the objects that use them (more precisely, a library will be used only if it contains a symbol that satisfies an undefined reference known at the time it is encountered). Move the -lmnlto the end of the command.
库必须在使用它们的对象之后列出（更准确地说，只有当库包含满足在遇到时已知的未定义引用的符号时才会使用库）。将 移动-lmnl到命令的末尾。
