How to load C .lib into managed c++/CLI project?

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C++

managed

CLI

Currently I need to load a C lib into my CLR project(managed c++/CLI).
All the header file and lib file have been added. But when compile the project, there are some errors and warning like below:

Errors:
error LNK2001: unresolved external symbol "extern "C" int __stdcall rsslDecodeMsg(struct RsslDecIterator *,union RsslMsg *)" (?rsslDecodeMsg@@$$J18YGHPAURsslDecIterator@@PATRsslMsg@@@Z)

Warning:
warning C4561: '__fastcall' incompatible with the '/clr' option: converting to '__stdcall'


Can someone kindly help me to solve this issue?
Thank you in advance.