Conversions from Unsigned Integral Types
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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