编译器libstdc ++版本与系统版本

根据根据我对ABI向前兼容性的理解，我可以使用g ++ 4.1.2构建，并期望代码能够在系统上运行，而系统的libstdc ++版本高于6.0.8，而不是早期版本，因为那样会有一个旧版本的ABI。

在同一台机器上，在/ usr / lib中有一个旧版本的libstdc ++：

任何见解都会被赞赏。

目录搜索列表。你可以这样看：

然而，列表通常会优先选择特定于编译器版本的库，如果有的话。

链接时间选择可能与运行时选择不同。

如果链接器命令包含 -rpath 选项（一些工具链供应商可能包含一个非标准的供应商），那么动态链接器将使用它在运行时找到合适的库。否则，系统将使用其默认库。

如果两个库不匹配，那么可能会发生不好的事情。 C库（通常是glibc）一直很小心地保持兼容性。 C ++库并不总是有这种奢侈品。近些年来这样更安全，但许多人仍然推荐不是混合和匹配。

I'm trying to understand how g++ selects which version of libstdc++ it links against and what it means when the "system" version of the library is different.

I'm using gcc/g++ 4.1.2, which according to the ABI Guidelines doc, includes libstdc++.so.6.0.8, and sure enough:

Based on my understanding of the ABI forward-compatibility, I can build with g++ 4.1.2 and expect the code to run on a system with a later version of libstdc++ than 6.0.8, but not on one with an earlier version, because that will have an older version of the ABI.

On the same machine there is an older version of libstdc++ in /usr/lib:

If I compile code using g++ 4.1.2 on this machine, then ldd it, I see the version of libstdc++ in /usr/lib referenced, which is 6.0.3:

This is expected, as /usr/lib is checked first. And the application runs fine.

My question is: what's happened here?

Has g++ 4.1.2 linked against the version of libstdc++.so that is part of that release (6.0.8)? If so, how come the executable can use the older version in /usr/lib at runtime, when that has an older ABI? Luck?

Or has g++ 4.1.2 picked up the /usr/lib version of libstdc++ (6.0.3) at link time and used that, because it resolves library paths in the same way as executables do at runtime? Can g++ do that, even if the libstdc++ is not its "own" version? What is the purpose of the libstdc++ version in g++4.1.2 (6.0.8)? Has it been used at all in this process?

Any insights appreciated.

GCC selects all libraries according to a directory search list. You can see it like this:

The list usually prefers libraries specific to the compiler version, if there is one.

However, the link-time choice may not be the same as the run-time choice.

If the linker command includes an -rpath option (some toolchain vendors may include a non-standard one) then the dynamic linker will use that to find the right libraries at run-time. Otherwise the system will use its default library.

If the two libraries are not well matches then bad things may happen. The C library (usually glibc) has always been careful to maintain compatibility. The C++ library has not always had this luxury. It's been safer in recent years but many people still recommend not mixing and matching.