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Integer conversions, including implicit and explicit (using a cast), must be guaranteed not to result in lost or misinterpreted data. The only integer type conversions that are guaranteed to be safe for all data values and all possible conforming implementations are conversions of an integral value to a wider type of the same signedness. From C99 Secttion 6.3.1.3:
When a value with integer type is converted to another integer type other than
_Bool, if the value can be represented by the new type, it is unchanged.Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or subtracting one more than the maximum value that can be represented in the new type
until the value is in the range of the new type.Otherwise, the new type is signed and the value cannot be represented in it; either the result is implementation-defined or an implementation-defined signal is raised.
Typically, converting an integer to a smaller type results in truncation of the high-order btis.
Non-Compliant Code Example
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