MSVC build errors > C2011

C2011: type redefinition

error C2011: 'sockaddr': 'struct' type redefinition

The compiler saw the definition of a class, struct, or enum twice in the same file, usually through headers.

Causes and fixes

1. A header has no include guard. Add #pragma once at the top of the header, so that including it twice defines its types once.
2. Two headers define the same type. Keep one definition, in one header, and include it from the other.
3. windows.h is included before winsock2.h. windows.h includes the old winsock.h, which redefines sockaddr: include winsock2.h first, or define WIN32_LEAN_AND_MEAN before windows.h.

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Related errors: C4430. See all guides.