[VL][MINOR] Replace NULL with nullptr

[beliefer]

What changes are proposed in this pull request?

This PR proposes to replace NULL with nullptr.
In C++, nullptr should always be used instead of NULL because:

• Provide better type security
• Avoid overloading and resolving ambiguity
• Better performance in template programming
• The code intent is clearer
• It is a standard practice in modern C++

Only consider using NULL when maintaining very old code repositories or interacting with C interfaces that only accept NULL.

How was this patch tested?

GA tests.

[wForget]

The original code is referenced from https://github.com/jemalloc/jemalloc/wiki/Use-Case%3A-Heap-Profiling. If NULL and nullptr are equivalent, this change looks good to me. @philo-he Could you please take a look?

[beliefer]

@wForget Thanks ! I think https://github.com/jemalloc/jemalloc/wiki/Use-Case%3A-Heap-Profiling just give us an use case.

[FelixYBW]

Can we add it to the https://github.com/apache/incubator-gluten/blob/main/dev/format-cpp-code.sh?

[philo-he]

Looks good. Just verified in my local build with enable_jemalloc_stats set to ON.

@FelixYBW, it seems clang-format doesn't support the check for using nullptr. @beliefer, could you add the following sentence in Constant section of CppCodingStyle.md to make developer aware of this convention?

Always use `nullptr` if you need a constant that represents a null pointer (`T*` for some `T`); use `0` otherwise for a zero value.

Reference:
https://github.com/facebookincubator/velox/blob/main/CODING_STYLE.md#constants

[FelixYBW]

@FelixYBW, it seems clang-format doesn't support the check for using nullptr.

I mean to add a sed like sed -i 's/NULL/nullptr/g'

[philo-he]

@FelixYBW, I feel that using sed command may cause unintentional replacement issue.

I just investigated Velox. It uses clang-tidy to check code style based on a configuration file, where we can set to replace NULL with nullptr, see https://github.com/facebookincubator/velox/blob/8a5a520fba06ab1fc10f124f3eb000bab886cd5d/.clang-tidy#L102.

If this sounds good to you, I can help enable clang-tidy in another PR. It can also cover some other code styles checks.

[FelixYBW]

If this sounds good to you, I can help enable clang-tidy in another PR. It can also cover some other code styles checks.

Thank you, @philo-he good idea.

[beliefer]

@philo-he @FelixYBW @wForget Thank you all