Conversion Expressions

The conversion unary operators string, int, char, float, oid and ident allows us to make the following conversions:

Operator	From	To	Returned Atom
string	any type	string	the string representation of the operand
int	int	int	the int operand
	char	int	the operand casted to an int
	float	int	the operand casted to an int
	string	int	the operand converted to an int
char	char	char	the char operand
	int	char	the operand casted to a char
	float	textttchar	the operand casted to a char
	string	char	the operand converted to a char
float	float	float	the float operand
	char	float	the operand casted to a float
	int	float	the operand casted to a float
	string	float	the operand converted to a float
oid	oid	oid	the oid operand
	string	oid	the string operand converted to an oid
ident	ident	ident	the ident operand
	string	ident	the string operand converted to an ident

These operators are used to perform an explicit conversion such as convert the string "123" to the integer 123, or to perform an explicit cast for numbers such as casting the integer 10 to the float 10.0. These operators evaluate first their operand before performing the conversion. If the operand type is valid, no error is raised even if its format is not valid, for instance: int "alpha" returns 0, while oid "aoaoai" returns NULL. Note that because of the precedence of these operators, parenthesis are necessary to make a conversion of a non-primary operand. For instance, string 1+2 is not valid: you should use string (1+2).

string operator

The string operator evaluates its operand and returns its string representation.

General Information
Operator	string
Syntax	string expr
Type	unary
Operand Type	any type
Result Type	string
Function	returns the string representation of any atom

Expression Examples
string 123.3	"1203.300000"
string 'a'	"a"
string first(select Person)	"71211.13.1486847:oid"
string &alpha	"::alpha"
string list(1, 2, 3+2)	"list(1, 2, 5)"
string (list("hello", 30) + list(10))	"list("hello", 30, 10)"
string (1+3)	"4"
string 1+3	raises an error

int operator

The int operator evaluates its operand and converts or casts it to an integer.
If the operand is the string, it converts it using the atoi C function. If the string is not a valid integer, it returns a 0.
If the operand is a char or float, it casts it to an integer.
If the operand is an integer, it returns it.

General Information
Operator	int
Syntax	int expr
Type	unary
Operand Type	int, char, float or string
Result Type	int
Function	returns the integer conversion or cast of the operand

Expression Examples
int 123.3	123
int 12	12
int 'a'	97
int "123"	123
int ("123" + "12")	12312
int alpha	the value of alpha converted or casted to an integer
int list(1, 2, 3)	raises an error

char operator

The char operator evaluates its operand and converts or casts it to a char.
If the operand is the string of length one, it returns the character of this string. If the string has several characters, it returns a '\000.
If the operand is a integer or float, it casts it to a character.
If the operand is a character integer, it returns it.

General Information
Operator	char
Syntax	char expr
Type	unary
Operand Type	int, char, float or string
Result Type	char
Function	returns the character conversion or cast of the operand

Expression Examples
char 123.3	{
char 'a'	'a'
char alpha	the value of alpha converted or casted to a character
char "a"	'a'
char "hello"	'^@'
char list(1, 2, 3)	raises an error

float operator

The float operator evaluates its operand and converts or casts it to a float.
If the operand is the string, it converts it using the atof C function. If the string is not a valid float, it returns a 0.0.
If the operand is a integer or float, it casts it to a float.
If the operand is a float, it returns it.

General Information
Operator	float
Syntax	float expr
Type	unary
Operand Type	int, char, float or string
Result Type	float
Function	returns the float conversion or cast of the operand

Expression Examples
float 123.0	123.0
float 123.3	123.3
float 'a'	97.000
float "123.0000000"	123.0
float ("123." + "12")	123.12
float "hello"	0.0
float alpha	the value of alpha converted or casted to a float
float list(1, 2, 3)	raises an error

oid operator

The oid operator evaluates its string operand and returns the corresponding oid. If the string does not denote a valid oid, the NULL oid is returned.
If the operand is an oid, it returns it.

General Information
Operator	oid
Syntax	oid expr
Type	unary
Operand Type	oid or string
Result Type	oid
Function	returns the oid denoted by the string operand

Expression Examples
oid "234.34.33:oid"	234.34.33:oid
oid 234.34.33:oid	234.34.33:oid
oid first(select Person)	returns the first person oid
oid 'a'	raises an error

ident operator

The ident operator evaluates its string operand and returns the corresponding identifier. If the operand is an identifier, it returns it.

General Information
Operator	ident
Syntax	ident expr
Type	unary
Operand Type	ident or string
Result Type	string
Function	returns the identifier denoted by the string operand

Expression Examples
ident "alpha"	alpha
ident "alpha#1x"	alpha#1x
ident "alpha" := 123	123, alpha has been assigned to 123
valof &(ident "alpha")	123
ident 'a'	raises an error