Conversions from Unsigned Integral Types

An unsigned integer is converted to a shorter unsigned or signed integer by truncating the high-order bits, or to a longer unsigned or signed integer by zero-extending (see the Conversions from Unsigned Integral Types table).

When the value with integral type is demoted to a signed integer with smaller size, or an unsigned integer is converted to its corresponding signed integer, the value is unchanged if it can be represented in the new type. However, the value it represents changes if the sign bit is set, as in the following example.

int j;
unsigned short k = 65533;

j = k;
printf_s( "%hd\n", j );   // Prints -3

If it cannot be represented, the result is implementation-defined. See Type-Cast Conversions for information on the Microsoft C compiler's handling of demotion of integers. The same behavior results from integer conversion or from type casting the integer.

Unsigned values are converted in a way that preserves their value and is not representable directly in C. The only exception is a conversion from unsigned long to float, which loses at most the low-order bits. Otherwise, value is preserved, signed or unsigned. When a value of integral type is converted to floating, and the value is outside the range representable, the result is undefined. (See Storage of Basic Types for information about the range for integral and floating-point types.)

The following table summarizes conversions from unsigned integral types.

Conversions from Unsigned Integral Types

From	To	Method
unsigned char	char	Preserve bit pattern; high-order bit becomes sign bit
unsigned char	short	Zero-extend
unsigned char	long	Zero-extend
unsigned char	unsigned short	Zero-extend
unsigned char	unsigned long	Zero-extend
unsigned char	float	Convert to long; convert long to float
unsigned char	double	Convert to long; convert long to double
unsigned char	long double	Convert to long; convert long to double
unsigned short	char	Preserve low-order byte
unsigned short	short	Preserve bit pattern; high-order bit becomes sign bit
unsigned short	long	Zero-extend
unsigned short	unsigned char	Preserve low-order byte
unsigned short	unsigned long	Zero-extend
unsigned short	float	Convert to long; convert long to float
unsigned short	double	Convert to long; convert long to double
unsigned short	long double	Convert to long; convert long to double
unsigned long	char	Preserve low-order byte
unsigned long	short	Preserve low-order word
unsigned long	long	Preserve bit pattern; high-order bit becomes sign bit
unsigned long	unsigned char	Preserve low-order byte
unsigned long	unsigned short	Preserve low-order word
unsigned long	float	Convert to long; convert long to float
unsigned long	double	Convert directly to double
unsigned long	long double	Convert to long; convert long to double

Microsoft Specific

For the Microsoft 32-bit C compiler, the unsigned int type is equivalent to the unsigned long type. Conversion of an unsigned int value proceeds in the same way as conversion of an unsigned long. Conversions from unsigned long values to float are not accurate if the value being converted is larger than the maximum positive signed long value.

END Microsoft Specific

See Also

Concepts

Assignment Conversions