链接时LD_LIBRARY_PATH和-L有什么区别？ [英] What is the difference between LD_LIBRARY_PATH and -L at link time?

问题描述

我在 link 时发现 LD_LIBRARY_PATH 存在问题（此问题与运行时间无关）。

b
$ b

当我运行make（这是一个使用g ++版本4.1.x的Linux系统）时，链接线看起来像这样：

  g ++ ao bo co -o myapp \ 
 -L ​​/ long / path / to / libs / \ 
 -L ​​/ another / long / path / \ 
 -labc -ldef -lghi 
  

-l <​​/ code> options引用共享库（如libabc.so），它们存在于 -L 选项指定的目录中。这些目录也出现在 LD_LIBRARY_PATH 中。如果我从> LD_LIBRARY_PATH 目录中删除这些目录，则可以使用该配置文件，并且可以运行该应用程序。 >，那么我得到一个错误行，如：

$ p $ / usr / bin / ld：找不到-labc


另一方面，如果我从 -L options，然后我得到很多警告，例如：

$ p $ / usr / bin / ld：warning：libabc。所以，需要/long/path/to/libs/libxyz.so，找不到
（尝试使用-rpath或-rpath-link）


以及更多错误，例如：



  / long / path /to/libs/libdef.so：对'Foo :: Bar< Baz> :: junk（Fred *）''
  


的未定义引用


有人可以解释 LD_LIBRARY_PATH 和 -L 之间的区别吗？我想深入了解这个东西，所以引用非常感谢！

另外，我必须添加到链接行以避免使用 LD_LIBRARY_PATH ？

编辑： < -L ，编译器建议尝试使用-rpath或-rpath-link。我以前从未见过makefile中的这些选项。你有吗？不知道这是否会帮助 LD_LIBRARY_PATH 问题。

LD_LIBRARY_PATH 的设置优先级最高，因此设置时，首先搜索由 LD_LIBRARY_PATH 提及的目录集甚至在目录的标准集合
之前。因此，在你的情况下，设置 LD_LIBRARY_PATH 会影响到查找

的库，这些库用 -l <​​/ code >选项。如果没有 LD_LIBRARY_PATH ，某些依赖关系

可能已从标准目录集中解析出来。



尽管设置 LD_LIBRARY_PATH 有助于调试并尝试更新版本的

a库在通用开发环境设置和部署中的使用被认为是不好的。



另请参阅来自Linux文档的这份HOWTO 了解共享库的更多详细信息

I'm having problems with LD_LIBRARY_PATH at link time (this question has nothing to do with run time).

The link line looks like this when I run make (this is a Linux system using g++ version 4.1.x):

g++ a.o b.o c.o -o myapp \
 -L/long/path/to/libs/ \
 -L/another/long/path/ \
 -labc -ldef -lghi

The -l options reference shared libraries (e.g., libabc.so) which exist in the directories specified by the -L options. Those directories also appear in LD_LIBRARY_PATH. With that configuration, the link is successful, and I can run the application.

If I remove the directories from LD_LIBRARY_PATH, then I get a single error line such as:

/usr/bin/ld: cannot find -labc

On the other hand, if I remove the directories from the list of -L options, then I get many warnings such as:

/usr/bin/ld: warning: libabc.so, needed by /long/path/to/libs/libxyz.so,
    not found (try using -rpath or -rpath-link)

and then many more errors, such as:

/long/path/to/libs/libdef.so: undefined reference to `Foo::Bar<Baz>::junk(Fred*)'

Can someone explain the difference between LD_LIBRARY_PATH and -L? I would like to understand this stuff in depth, so references are greatly appreciated!

Also, what do I have to add to the link line to avoid using LD_LIBRARY_PATH?

EDIT: When directories were missing from -L, the compiler suggested to "try using -rpath or -rpath-link". I don't think I've ever seen those options in a makefile before. Have you? Not sure if that would help the LD_LIBRARY_PATH problem though.

解决方案

The settings of LD_LIBRARY_PATH has the highest precedence, so when it is set, the set of directories mentioned by LD_LIBRARY_PATH are searched first even before the standard set
of directories. So in your case setting of LD_LIBRARY_PATH is influencing the lookup of
the libraries mentioned with -l option. Without LD_LIBRARY_PATH some of the dependencies
might have been resolved from the standard set of directories.

Though setting of LD_LIBRARY_PATH help with debugging and to try out a newer version of
a library its usage in the general development environment setup and deployment is considered bad.

Also refer this HOWTO from Linux Documentation for more details on Shared Libraries

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