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# qstring-unneeded-heap-allocations
Finds places with unneeded memory allocations due to temporary `QString`s.
Here's a summary of usages that allocate:
1. `QString s = "foo"; // Allocates, use QStringLiteral("foo") instead`
2. `QString s = QLatin1String("foo"); // Allocates, use QStringLiteral("foo") instead`
2.1 `QString s = QLatin1String(""); // No allocation. QString is optimized for this case, so it's safe for empty literals`
3. `QString s = QStringLiteral("foo"); // No allocation`
4. `QString s = QString::fromLatin1("foo"); // Allocates, use QStringLiteral`
5. `QString s = QString::fromUtf8("foo"); // Allocates, use QStringLiteral`
6. `s == "foo" // Allocates, use QLatin1String`
7. `s == QLatin1String("foo) // No allocation`
8. `s == QStringLiteral("foo") // No allocation`
9. `QString {"append", "compare", "endsWith", "startsWith", "indexOf", "insert",`
` "lastIndexOf", "prepend", "replace", "contains" } // They all have QLatin1String overloads, so passing a QLatin1String is ok.`
10. `QString::fromLatin1("foo %1").arg(bar) // Allocates twice, replacing with QStringLiteral makes it allocate only once.`
#### Fixits
fix-qlatin1string-allocations // To replace QLatin1String with QStringLiteral only where it was allocating before
fix-fromLatin1_fromUtf8-allocations // To replace fromLatin1() and fromUtf8() so it doesn't allocate
fix-fromCharPtrAllocations // To replace raw string literals so it doesn't allocate
Example:
export CLAZY_FIXIT="fix-fromCharPtrAllocations"
#### Pitfalls
- `QStringLiteral` might make your app crash at exit if plugins are involved.
See:
<https://blogs.kde.org/2015/11/05/qregexp-qstringliteral-crash-exit> and
<http://lists.qt-project.org/pipermail/development/2015-November/023681.html>
- Also note that MSVC crashes when `QStringLiteral` is used inside initializer lists. For that reason no warning or fixit is emitted for this case unless you set an env variable:
export CLAZY_EXTRA_OPTIONS="qstring-allocations-no-msvc-compat"
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