如何解决MySQL C++ Connector与OpenSSL的符号重复定义问题？

项目同时引入MySQL C++ Connector和用于套接字的OpenSSL库，编译时触发大量LNK2005符号重复定义错误，具体错误信息如下：

1>libcrypto.lib(libcrypto-lib-x509_d2.obj) : error LNK2005: X509_STORE_load_locations already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-ct_policy.obj) : error LNK2005: CT_POLICY_EVAL_CTX_free already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-ct_policy.obj) : error LNK2005: CT_POLICY_EVAL_CTX_set1_cert already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-ct_policy.obj) : error LNK2005: CT_POLICY_EVAL_CTX_set1_issuer already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-ct_policy.obj) : error LNK2005: CT_POLICY_EVAL_CTX_set_shared_CTLOG_STORE already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-ct_policy.obj) : error LNK2005: CT_POLICY_EVAL_CTX_set_time already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-srp_lib.obj) : error LNK2005: SRP_Calc_A already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-srp_lib.obj) : error LNK2005: SRP_Calc_server_key already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-srp_lib.obj) : error LNK2005: SRP_Verify_A_mod_N already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-srp_lib.obj) : error LNK2005: SRP_Verify_B_mod_N already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-srp_lib.obj) : error LNK2005: SRP_check_known_gN_param already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-srp_lib.obj) : error LNK2005: SRP_get_default_gN already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_INFO_free already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_INFO_get0_CERT already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_INFO_get0_NAME already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_INFO_get_type already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_close already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_eof already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_error already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_load already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)
1>libcrypto.lib(libcrypto-lib-store_lib.obj) : error LNK2005: OSSL_STORE_open already defined in mysqlcppconn-static.lib(libcrypto-1_1-x64.dll)

当前项目配置 #

包含目录 #

\asio-1.24.0\include
\openssl\Lib\x64\Release\include
\MySQL\Connector C++ 8.0\include\jdbc

链接器输入 #

\openssl\Lib\x64\Release\lib\libcrypto.lib
\openssl\Lib\x64\Release\lib\libssl.lib
crypt32.lib
mysqlcppconn-static.lib

可行解决方案 #

1. 替换为动态版MySQL Connector库 #

静态版mysqlcppconn-static.lib确实内置了OpenSSL的符号，换成动态版mysqlcppconn.lib即可，运行时要保证mysqlcppconn.dll在可执行文件路径下。动态版不会把OpenSSL符号打包进去，从根源避免冲突。

2. 调整链接顺序 #

如果必须使用静态版MySQL库，调整链接器输入的顺序：把mysqlcppconn-static.lib放在libcrypto.lib和libssl.lib的前面。链接器会优先使用先出现的库中的符号，这样就不会触发重复定义报错。

3. 使用无SSL版本的MySQL Connector静态库 #

部分版本的MySQL C++ Connector提供了不带SSL支持的静态库（命名通常带有-no-ssl后缀），如果你的场景不需要MySQL的SSL连接，可以选择这类库，彻底规避OpenSSL符号冲突。

4. 统一OpenSSL版本 #

检查MySQL Connector内置的OpenSSL版本和你手动引入的OpenSSL版本是否一致。版本不匹配也会导致符号冲突，可以尝试换成和MySQL内置版本一致的OpenSSL库，或者自行编译MySQL Connector并指定使用你当前的OpenSSL版本。

内容的提问来源于stack exchange，提问作者abdul