This is a draft version of a MISRA C++ 202x rule proposed for public review.
MISRA Rule 6.9.2
Category: Advisory
Analysis Type: Decidable,Single Translation Unit
Amplification
This rule applies to the names of integral types constructed using the keywords char, short, int,
long, signed and unsigned (ignoring any cv-qualification). It does not apply to the use of plain
char.
Rationale
It is implementation-defined how much storage is required for any object of the standard signed integer types or standard
unsigned integer types. When the amount of storage being used is important, the use of types having specified widths makes it clear how much
storage is being reserved for each object.
The C++ Standard Library header file [1] <cstdint> often provides a suitable set of integer types having specified
widths. If a project defines its own type aliases, it is good practice to use static_assert to validate any size assumptions. For
example:
using torque_t = unsigned short;
static_assert( sizeof( torque_t ) >= 2 );
Notes:
- Adherence to this rule does not prevent integer promotion, which is influenced by the implemented size of
int and the type used
for an alias. For example, an expression of type int16_t will only be promoted if the aliased type has a rank lower than that of
int. The presence or absence of integer promotion may have an influence on overload resolution.
- Strong typing, which may be provided by class or enum types, is more robust than the use of type aliases to represent specific width types.
Exception
- The names of the standard signed integer types and standard unsigned integer types may be used to define a type alias.
- The name
int may be used for:
- The parameter to a postfix operator, which must use that type; and
- The return type of
main; and
- The
argc parameter to main.
Example
#include <cstdint>
int x = 0; // Non-compliant - use of int
int32_t y = 0; // Compliant
int_least32_t z = 0; // Compliant
using torque_t = int; // Compliant by exception #1
torque_t w = 0;
class C
{
public:
C operator++ ( int ); // Compliant by exception #2.1
};
int main() { } // Compliant by exception #2.2
int main( int argc, char * argv[] ) { } // Compliant by exception #2.2 and #2.3
Glossary
[1] Header file
A header file is considered to be any file that is included during preprocessing (for example via the #include directive),
regardless of its name or suffix.
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