# V2653\. MISRA\. The small integer variants of the minimum\-width integer constant macros should not be used\.

This diagnostic rule is based on the [MISRA](https://misra.org.uk/) \(Motor Industry Software Reliability Association\) software development guidelines\.

This diagnostic rule is relevant only for C\.

According to [C11](https://open-std.org/JTC1/SC22/WG14/www/docs/n1570.pdf#page=308) \(Section 7\.20\.1\.2\), the minimum\-width macros of integer constants should be expanded into an [integer constant expression](https://en.cppreference.com/w/c/language/constant_expression.html)\. According to [C11](https://open-std.org/JTC1/SC22/WG14/www/docs/n1570.pdf#page=312) \(Section 7\.20\.4\.3\), the expression should comply with `#if` directives, and its type should be the same as if [integer promotion](https://en.cppreference.com/w/c/language/conversion.html#Integer_promotions) had been applied to the macro argument\.

Using minimum\-width integer constant macros is not recommended, as it leads to confusion with substituted types\.

The example:

```cpp
void function_u8(uint8_t value){}
void function_int(int value) {}

#define MACRO_U8(Z) _Generic((Z)              \
                     , uint8_t: function_u8   \
                     , default: function_int)(Z)

void foo(void)
{
  MACRO_U8(UINT8_C(8));    // <=
}
```

`UINT8_C` is a C macro defined in standard header files \(e\.g\., `<stdint.h>`\) to denote unsigned 8\-bit integer constants\. It is used to provide cross\-platform and cross\-compiler portability\.

The result of expanding the `UINT8_C` macro is expected to be of `uint8_t` type\. However, after applying integer promotion, since the rank of `uint8_t` is less than `int`, the result will be the same as if the argument had been substituted into the code without changes, as the integer constant `8`\.

As a result, [\_Generic selection](https://en.cppreference.com/w/c/language/generic.html) chooses the `function_int(int value)` association instead of the expected `function_u8(uint8_t value)`\.

The fixed code:

```cpp
void function_u8(uint8_t value){}
void function_int(int value) {}

#define MACRO_U8(Z) _Generic((Z)              \
                     , uint8_t: function_u8   \
                     , default: function_int)(Z)

void foo(void)
{
  MACRO_U8((uint8_t)(8));
}
```