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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

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