链接器告诉我它无法解析符号，但它们在那里? [英] linker tells me it can't resolve symbols, but they're there?

问题描述

我正在尝试使用我编写的库来编译一个简单的测试应用程序.这在其他机器上编译并运行良好.

I am trying to compile a simple test app using a library I've written. This compiles and runs fine on other machines.

我在/usr/lib 有 libroller.so.我正在编译一个 main.cpp:

I have libroller.so available at /usr/lib. I'm compiling a main.cpp as such:

g++ -g3 -Wall -I"../../" -lrt -lroller -o rap main.o

它抱怨许多错误，例如:

It complains of numerous errors such as:

/....../main.cpp:51: undefined reference to `Log::i(char const*, ...)'

但是，我知道这些存在于这里:

However, I know that these exist in this so:

nm -Ca /usr/lib/libroller.so | grep "Log::i"            
00000000001f5d50 T Log::i(char const*, ...)
0000000000149530 W Log::i(std::string const&)

两者都是 64 位:

file /usr/lib/libroller.so           
/usr/lib/libroller.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, not stripped

file main.o   
main.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped

不同于 GCC 和 ld 找不到导出的符号...但它们就在那里！ 我很确定这些符号是已定义的.相同的 .so 使用一些相同的符号与另一个一起使用.

Unlike GCC and ld can't find exported symbols...but they're there! I'm pretty sure these symbols are defined. The same .so works with another using some of the same symbols.

编辑/回答:对象的顺序很重要.必须在库之前放置 main.o.我猜链接器在到达 main.o 之前没有要处理的未解析符号——这是其列表中的最后一个对象.我仍然有点困惑为什么这在其他机器上工作了好几个月......

EDIT/ANSWER: The order of objects is important. Placing main.o before the libraries was necessary. I'm guessing the linker had no unresolved symbols to deal with until it got to main.o -- which was the last object in its list. I'm still a little confused as to why this worked on other machines for many months...

推荐答案

更改:

g++ -g3 -Wall -I"../../" -lrt -lroller -o rap main.o

到:

g++ -g3 -Wall main.o -lroller -lrt -o rap 

链接顺序很重要(在这种情况下，-I 是多余的).

Link order matters (and the -I is redundant in this instance).

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