detail::string_impl: zero-initialize union and avoid redundant data() in term()

[Tyagiquamar]

Description

Fixes #1133.

When constructing string_impl via the SBO path (such as string_impl(0, sp) or the default constructor), uninitialized bytes in the union could trigger -Wmaybe-uninitialized compiler warnings or sanitizer reports during inlining of member functions.

• Zero-initializes s_{} in string_impl() and string_impl(std::size_t, storage_ptr const&).
• In term(), directly indexes reinterpret_cast<char*>(p_.t + 1)[n] = 0; in the non-SBO branch instead of invoking data() which performs a redundant branch check.

Testing

• Tested with boost::json unit test suite.

[cppalliance-bot]

An automated preview of the documentation is available at https://1206.json.prtest2.cppalliance.org/libs/json/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-10-04 16:32:55 UTC

[cppalliance-bot]

GCOVR code coverage report https://1206.json.prtest2.cppalliance.org/gcovr/index.html
LCOV code coverage report https://1206.json.prtest2.cppalliance.org/genhtml/index.html
Coverage Diff Report https://1206.json.prtest2.cppalliance.org/diff-report/index.html

Build time: 2026-10-04 16:59:37 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.98%. Comparing base (fc70d23) to head (2964fb7).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1206   +/-   ##
========================================
  Coverage    93.98%   93.98%           
========================================
  Files           85       85           
  Lines         8973     8975    +2     
========================================
+ Hits          8433     8435    +2     
  Misses         540      540           

Files with missing lines	Coverage Δ
include/boost/json/detail/impl/string_impl.ipp	100.00% <100.00%> (ø)
include/boost/json/detail/string_impl.hpp	100.00% <100.00%> (ø)

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[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/1206/pullrequest.html