Question

I want to statically compile my program against another static library, for this example I'm using zeromq. Here is my CMakeLists.txt

cmake_minimum_required(VERSION 2.6)
add_executable( test test.cpp )
find_library(ZMQ NAMES libzmq.a)
message(STATUS ${ZMQ})
target_link_libraries( test ${ZMQ} )

It finds the .a file when I run mkdir build && cd build && cmake ..

-- /usr/local/lib/libzmq.a

However, if I examine the link.txt file, the library is dynamically linked:

/usr/bin/c++ CMakeFiles/test.dir/test.cpp.o \
    -o test -rdynamic /usr/local/lib/libzmq.a

The weird bit is that if I move the file to a different directory, say /usr/lib and run cmake .. once more, it locates the new path to the library:

-- /usr/lib/libzmq.a

But now it has magically changed to static linking:

/usr/bin/c++ CMakeFiles/test.dir/test.cpp.o \
    -o test -rdynamic -Wl,-Bstatic -lzmq -Wl,-Bdynamic

The same thing applies to other libraries I'm linking to.

Why are all my libraries in /usr/local/lib being dynamically linked?

Answer 1

你不应该直接使用路径，而是创建一个imported target，所以你可以明确地声明它是静态的：

cmake_minimum_required(VERSION 2.6)
add_executable( test test.cpp )

find_library(zmq_location NAMES libzmq.a)
message(STATUS ${zmq_location})

add_library(zmq STATIC IMPORTED)
set_target_properties(zmq PROPERTIES IMPORTED_LOCATION ${zmq_location})

target_link_libraries( test zmq )

这可能会导致库出现以动态关联，但cmake source code has the answer：

如果目标不是静态库，请确保链接类型是共享的。这是因为动态模式链接可以处理共享库和静态库，但静态模式只能处理静态库。如果先前的用户项目将链接类型更改为我们需要确保它回归共享。

基本上，如果当前处于动态模式，它会让链接器处理检测到库是静态的。

Answer 2

关于/usr/local/lib和/usr/lib之间区别的原始问题的答案是，默认情况下，/usr/local/lib不是隐式链接目录之一。因此，快速解决方法是在配置中包含此行：

set(CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES /usr/local/lib ${CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES})

但是，正如本other answer所指出的那样，直接引用文件不是一种方法，而应该使用add_library。

CMake dynamically links `.a` files in `/usr/local/lib`

2 个答案: