================
@@ -0,0 +1,227 @@
+.. title:: clang-tidy - portability-avoid-platform-specific-fundamental-types
+
+portability-avoid-platform-specific-fundamental-types
+=====================================================
+
+Finds fundamental types (e.g. `int`, `float`) and recommends using typedefs
+or fixed-width types instead to improve portability across different platforms.
+
+This check detects fundamental types (``int``, ``short``, ``long``, ``float``,
+``char`` and their ``unsigned`` or ``signed`` variants) and warns against
their
+use due to non-standard platform-dependent behavior. For example, ``long`` is
+64 bits on Linux but 32 bits on Windows. There is no standard rationale or
+intent for the sizes of these types.
+
+Instead of fundamental types, use fixed-width types such as ``int32_t`` or
+implementation-defined types with standard semantics, e.g. ``int_fast32_t``
for
+the fastest integer type greater than or equal to 32 bits.
+
+Examples
+--------
+
+.. code-block:: c++
+
+ // Bad: platform-dependent fundamental types
+ int global_int = 42;
+ short global_short = 10;
+ long global_long = 100L;
+ unsigned long global_unsigned_long = 100UL;
+
+ void function_with_int_param(int param) {
+ // ...
+ }
+
+ int function_returning_int() {
+ return 42;
+ }
+
+ struct MyStruct {
+ int member_int;
+ long member_long;
+ };
+
+.. code-block:: c++
+
+ // Good: use fixed-width types or typedefs
+ #include <cstdint>
+
+ int32_t global_int32 = 42;
+ int16_t global_int16 = 10;
+ int64_t global_int64 = 100L;
+ uint64_t global_uint64 = 100UL;
+
+ void function_with_int32_param(int32_t param) {
+ // ...
+ }
+
+ int32_t function_returning_int32() {
+ return 42;
+ }
+
+ struct MyStruct {
+ int32_t member_int32;
+ int64_t member_int64;
+ };
+
+The check will also warn about typedef declarations that use fundamental types
+as their underlying type:
+
+.. code-block:: c++
+
+ // Bad: typedef using fundamental type
+ typedef long long MyLongType;
+ using MyIntType = int;
+
+.. code-block:: c++
+
+ // Good: use descriptive names or fixed-width types
+ typedef int64_t TimestampType;
+ using CounterType = uint32_t;
+
+Rationale
+---------
+
+Fundamental types have platform-dependent sizes and behavior:
+
+- ``int`` is typically 32 bits on modern platforms but is only guaranteed to be
+ 16 bits by the spec
+- ``long int`` is 32 bits on Windows but 64 bits on most Unix systems
+- ``double`` is typically 64-bit IEEE754, but on some microcontrollers without
+ a 64-bit FPU (e.g. certain Arduinos) it can be 32 bits
+- ``char`` is signed on ARM and unsigned on x86
+
+The C++ specification does not define these types beyond their minimum sizes.
----------------
5chmidti wrote:
+- on the wording of this sentence, since the standard partially defines the
behavior of types (e.g., truncation is only defined for some, but still
something that is defined at least for some of these types)
https://github.com/llvm/llvm-project/pull/146970
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