Somebody know how to use dynamic link so file in cygwin?
g++ in cygwin cannot recognize the option '-rdynamic'.
If I have a so file(dynamic link), where should I put it in cygwin?
I caanot find any so file in cygwin.

Quote: -rdynamic: Pass the flag -export-dynamic to the ELF linker, on targets that support it. This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. This option is needed for some uses of "dlopen" or to allow obtaining backtraces from within a program.

Windows and Cygwin target PE/COFF rather than ELF. An ELF shared object ("so") would be instead a dynamic-link library (DLL). Here's some documentation on DLLs in Cywgin: Building and Using DLLs.