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This diagnostic rule is based on the MISRA (Motor Industry Software Reliability Association) software development guidelines.
This diagnostic rule is relevant only for C.
The C language allows much flexibility in conversion between arithmetic types, but it can also lead to hidden problems such as loss of sign, loss value, or loss of precision.
The MISRA C standard defines its own type model, called the essential type model.
Using the essential type model can help avoid many non-obvious issues mentioned above by assigning values of the same essential type to variables. Within this model, a variable of a wider type can be assigned a value of a narrower essential type. Implicit conversions between different essential types are forbidden.
Exceptions:
essential signed type can be assigned to a variable of the essential unsigned type if its value can be represented by this type.{ 0 } initializer can be used to initialize an aggregate type or union.The example:
typedef enum ENUM {ONE} ENUM;
void Positive(signed char x)
{
unsigned char uchr = x; // <=
unsigned short usht = x; // <=
unsigned int uit = x; // <=
unsigned long ulg = x; // <=
unsigned long long ullg = x; // <=
long double ld = 0.0;
double d = ld; // <=
float f = d; // <=
ENUM e = x; // <=
}The fixed code:
enum {ONE = 1, TWO, THREE, FOUR, FIVE, SIX,
MUCH = 123123, MORE = 0x7FFFFFFF-1};
void Negative()
{
signed char c = ONE; // ok
signed short h = TWO; // ok
signed int i = THREE; // ok
signed long long ll = FOUR; // ok
unsigned char uc = FIVE; // ok
unsigned short uh = SIX; // ok
unsigned int ui = MUCH; // ok
unsigned long long ull = MORE; // ok
float f = 0.0f; // ok
double d = f; // ok
long double ld = d; // ok
ENUM e = c; // ok
}This diagnostic rule is classified as:
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