Conversions from Floating-Point Types

A float value converted to a double or long double, or a double converted to a long double, undergoes no change in value. A double value converted to a float value is represented exactly, if possible. Precision may be lost if the value cannot be represented exactly. If the result is out of range, the behavior is undefined. See Limits on Floating-Point Constants for the range of floating-point types.

A floating value is converted to an integral value by first converting to a long, then from the long value to the specific integral value. The decimal portion of the floating value is discarded in the conversion to a long. If the result is still too large to fit into a long, the result of the conversion is undefined.

Microsoft Specific

When converting a double or long double floating-point number to a smaller floating-point number, the value of the floating-point variable is truncated toward zero when an underflow occurs. An overflow causes a run-time error. Note that the Microsoft C compiler maps long double to type double.

END Microsoft Specific

The following table summarizes conversions from floating types.

Conversions from Floating-Point Types

From	To	Method
float	char	Convert to long; convert long to char
float	short	Convert to long; convert long to short
float	long	Truncate at decimal point. If result is too large to be represented as long, result is undefined.
float	unsigned short	Convert to long; convert long to unsigned short
float	unsigned long	Convert to long; convert long to unsigned long
float	double	Change internal representation
float	long double	Change internal representation
double	char	Convert to float; convert float to char
double	short	Convert to float; convert float to short
double	long	Truncate at decimal point. If result is too large to be represented as long, result is undefined.
double	unsigned short	Convert to long; convert long to unsigned short
double	unsigned long	Convert to long; convert long to unsigned long
double	float	Represent as a float. If double value cannot be represented exactly as float, loss of precision occurs. If value is too large to be represented as float, the result is undefined.
long double	char	Convert to float; convert float to char
long double	short	Convert to float; convert float to short
long double	long	Truncate at decimal point. If result is too large to be represented as long, result is undefined.
long double	unsigned short	Convert to long; convert long to unsigned short
long double	unsigned long	Convert to long; convert long to unsigned long
long double	float	Represent as a float. If double value cannot be represented exactly as float, loss of precision occurs. If value is too large to be represented as float, the result is undefined.
long double	double	The long double value is treated as double.

Conversions from float, double, or long double values to unsigned long are not accurate if the value being converted is larger than the maximum positive long value.

See Also

Concepts

Assignment Conversions