# 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 This check supports a fixit to rewrite your code. See the README.md on how to enable it. #### 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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