C++：链接到两个版本的 opencv。 如何告诉链接器选择特定版本

Question

Description

I have the following problem:

• I am developing the library libmy_code.so

• I need to link against a closed source library libclosed_source.so over which I have no control

• libclosed_source.so is statically linked against opencv 3.2.0

• libclosed_source.so has exported all symbols (also those from opencv 3.2.0 which I do not want)

• My library libmy_code.so also needs the newer version opencv 3.4.11

• I use CMake as the build system

See the following diagram

                                           +-------------+
                                      +--->|libmy_code.so+<-------+
                                      |    +-------------+        |
                                      |                           |
                    Statically linked |                           |dynamically linked
                                      |                           |
                                      |                           |
                                      |                           |
                                      |                           |
                                      |                   +-------+-----------+
                                      |                   |libclosed_source.so|
                                      |                   +-------------------+
                                      |                           ^
                                      |                           | Statically linked
                                      |                           |
                                  +---+---------+           +-----+------+
                                  |OpenCV 3.4.11|           |Opencv 3.2.0|
                                  +-------------+           +------------+

Problem

• My library libmy_code.so uses cv::resize. The CMake build system correctly locates cv::resize in the headers of OpenCV 3.4.11 (I use find_package(OpenCV) and point it to the opencv 3.4.11 install).

• However the linker links cv::resize to libclosed_source.so (which contains the Opencv3.2.0 version of cv::resize statically).

• My build system runs in a docker container which definitely does not have opencv 3.2.0.

• The closest question I have found is this

How can I tell the linker not to linker opencv functions libmy_code.so to libclosed_source.so but directly to Opencv 3.4.11 ??

Answer 1

Solution

My solution to the problem is to load libclosed_source.so dynamically per dlopen with RTLD_DEEPBIND|RTLD_LOCAL into libmy_code.so. This way libmy_code.so can use opencv 3.4.11 and libclosed_source.so can still use opencv 3.2.0.

The executable that was linked against libmy_code.so had to be compiled with -fPIC to prevent problems with libstdc++, more to that in Weird interaction of RTLD_DEEPBIND, Position independent Code (PIC) and C++ STL (std::cout)