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Unboxing is the operation of converting a value of a reference type (previously boxed) into a value of a value type. [15] Unboxing in C# requires an explicit type cast. Example:
The integer is: 16777217 The float is: 16777216.000000 Their equality: 1 Note that 1 represents equality in the last line above. This odd behavior is caused by an implicit conversion of i_value to float when it is compared with f_value. The conversion causes loss of precision, which makes the values equal before the comparison. Important takeaways:
Information about the actual properties, such as size, of the basic arithmetic types, is provided via macro constants in two headers: <limits.h> header (climits header in C++) defines macros for integer types and <float.h> header (cfloat header in C++) defines macros for floating-point types. The actual values depend on the implementation.
In addition to the assumption about bit-representation of floating-point numbers, the above floating-point type-punning example also violates the C language's constraints on how objects are accessed: [3] the declared type of x is float but it is read through an expression of type unsigned int.
If no invalid value can be found for a type (for example in case of an unconstraint integer type), a valid, yet predictable value is chosen instead. ^f In Rust, if no initial value is given to a let or let mut variable and it is never assigned to later, there is an "unused variable" warning .
In the floating-point case, a variable exponent would represent the power of ten to which the mantissa of the number is multiplied. Languages that support a rational data type usually allow the construction of such a value from two integers, instead of a base-2 floating-point number, due to the loss of exactness the latter would cause.
A 2-bit float with 1-bit exponent and 1-bit mantissa would only have 0, 1, Inf, NaN values. If the mantissa is allowed to be 0-bit, a 1-bit float format would have a 1-bit exponent, and the only two values would be 0 and Inf. The exponent must be at least 1 bit or else it no longer makes sense as a float (it would just be a signed number).
A compiler may use the static type of a value to optimize the storage it needs and the choice of algorithms for operations on the value. In many C compilers the float data type, for example, is represented in 32 bits, in accord with the IEEE specification for single-precision floating point numbers.