Uninitialized bool serialized and used

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#1

Source File:
/Engine/Source/Runtime/NetworkFileSystem/Private/NetworkFileServerConnection.cpp

Description:
bReadOnly has automatic storage duration but is not initialized, then gets serialized and used in a call to SetReadOnly.

Reference:
https://github.com/EpicGames/UnrealEngine/blob/69b5693c869697b828e1f2c24004ff1481b5fb98/Engine/Source/Runtime/NetworkFileSystem/Private/NetworkFileServerConnection.cpp#L557

Reference Line: 557

Notes: Found with the aid of static program analysis (Cppcheck).

#2

Hi rejecht,

Is this causing any errors or crashes for you? If so, could you provide any relevant log files or callstacks?

#3

Hi Tim,

You may dismiss the original bug report. It turns out the classes do the right thing after a closer look at what FArchive does, however, the C++ code tells me the wrong thing semantically.

If the code had read…
In >> bReadOnly;

…it would be clear to a C++ programmer that bReadOnly gets initialized at that point.

The code instead reads…
In << bReadOnly;

Standard C++ language semantics for the above means to take the value of bReadOnly (uninitialized in this case) and write it to In. Since that didn’t make much sense, I had a closer look at FArchive, which rewrites the meaning of the operator <<.

#4

Hi rejecht,

I noticed that oddity as well when I was looking at the code in NetworkFileServerConnection.cpp. Unfortunately I do not think this is something that we will make clearer at some point.