GH-48744: [C++][Parquet] Fix undefined behavior in memcpy with nullptr #48745
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…nullptr When ByteArray has len=0 and ptr=nullptr (the default-constructed state), calling std::memcpy with nullptr is undefined behavior according to the C++ standard, even when size is 0. This commit adds guards to check len > 0 before calling memcpy in: - TypedStatisticsImpl<ByteArrayType>::Copy (statistics.cc) - DictDecoderImpl<ByteArrayType>::SetDict (decoder.cc) - Test utilities (statistics_test.cc, column_writer_test.cc) Claude-Generated-By: Claude Code (cli/claude-opus-4-5=100%) Claude-Steers: 1 Claude-Permission-Prompts: 8 Claude-Escapes: 1
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Rationale for this change
As noted by @wgtmac in #48717 (comment), calling
std::memcpywith a nullptr source is undefined behavior according to the C++ standard, even when the size is 0.When
ByteArrayhaslen=0andptr=nullptr(the default-constructed state pertypes.h:649), the current code invokes UB.What changes are included in this PR?
Added guards to check
len > 0before callingmemcpyin:TypedStatisticsImpl<ByteArrayType>::Copyinstatistics.ccDictDecoderImpl<ByteArrayType>::SetDictindecoder.ccstatistics_test.ccandcolumn_writer_test.ccAre these changes tested?
Existing tests pass. The fix prevents potential UB that sanitizers or optimizing compilers could exploit.
Are there any user-facing changes?
No.