Add note about RC_INVOKED

1 files changed, 13 insertions, 0 deletions

diff --git a/lib/lz4.h b/lib/lz4.h
index 383d9666..491c6087 100644
--- a/lib/lz4.h
+++ b/lib/lz4.h
@@ -311,6 +311,19 @@ LZ4LIB_API int LZ4_decompress_safe_partial (const char* src, char* dst, int srcS
 ***********************************************/
 typedef union LZ4_stream_u LZ4_stream_t;  /* incomplete type (defined later) */
 
+/**
+ Note about RC_INVOKED
+
+ - RC_INVOKED is predefined symbol of rc.exe (the resource compiler which is part of MSVC/Visual Studio).
+   https://docs.microsoft.com/en-us/windows/win32/menurc/predefined-macros
+
+ - Since rc.exe is a legacy compiler, it truncates long symbol (> 30 chars)
+   and reports warning "RC4011: identifier truncated".
+
+ - To eliminate the warning, we surround long preprocessor symbol with
+   "#if !defined(RC_INVOKED) ... #endif" block that means
+   "skip this block when rc.exe is trying to read it".
+*/
 #if !defined(RC_INVOKED) /* https://docs.microsoft.com/en-us/windows/win32/menurc/predefined-macros */
 #if !defined(LZ4_STATIC_LINKING_ONLY_DISABLE_MEMORY_ALLOCATION)
 LZ4LIB_API LZ4_stream_t* LZ4_createStream(void);