S-Lang Run-Time Library Reference: Version 1.4.0: Data-Type Conversion Functions

Next Previous Contents

## 9. Data-Type Conversion Functions

## 9.1 _slang_guess_type

Synopsis

  Guess the data type that a string represents.

Usage

  `DataType_Type _slang_guess_type (String_Type s)`

Description

  This function tries to determine whether its argument `s` represents an integer or a floating point number. If it appears to be neither, then a string is assumed. It returns one of three values depending on the format of the string `s`:

  > `

  >         Integer_Type     :   If it appears to be an integer
  >         Double_Type      :   If it appears to be a double
  >         String_Type      :   Anything else.

  > `

  For example, `_slang_guess_type("1e2")` returns `Double_Type` but `_slang_guess_type("e12")` returns `String_Type`.
See Also

  `integer, string, double`

## 9.2 _typeof

Synopsis

  Get the data type of an object

Usage

  `DataType_Type _typeof (x)`

Description

  This function is similar to the `typeof` function except in the case of arrays. If the object `x` is an array, then the data type of the array will be returned. otherwise `_typeof` returns the data type of `x`.

Example

  > `

  >       if (Integer_Type == _typeof (x))
  >         message ("x is an integer or an integer array");

  > `

See Also

  `typeof, array_info, _slang_guess_type, typecast`

## 9.3 atof

Synopsis

  Convert a string to a double precision number

Usage

  `Double_Type atof (String_Type s)`

Description

  This function converts a string `s` to a double precision value and returns the result. It performs no error checking on the format of the string. The function `_slang_guess_type` may be used to check the syntax of the string.

Example

  > `

  >          define error_checked_atof (s)
  >          {
  >             switch (_slang_guess_type (s))
  >             {
  >                case Double_Type:
  >                  return atof (s);
  >             }
  >             {
  >                case Integer_Type:
  >                  return double (integer (s));
  >             }

  >             verror ("%s is is not a double", s);
  >         }

  > `

See Also

  `typecast, double, _slang_guess_type`

## 9.4 char

Synopsis

  Convert an ascii value into a string

Usage

  `String_Type char (Integer_Type c)`

Description

  The `char` function converts an integer ascii value `c` to a string of unit length such that the first character of the string is `c`. For example, `char('a')` returns the string `"a"`.

See Also

  `integer, string, typedef`

## 9.5 define_case

Synopsis

  Define upper-lower case conversion.

Usage

  `define_case (Integer_Type ch_up, Integer_Type ch_low);`

Description

  This function defines an upper and lowercase relationship between two characters specified by the arguments. This relationship is used by routines which perform uppercase and lowercase conversions. The first integer `ch_up` is the ascii value of the uppercase character and the second parameter `ch_low` is the ascii value of its lowercase counterpart.

See Also

  `strlow, strup`

## 9.6 double

Synopsis

  Convert an object to double precision

Usage

  `result = double (x)`

Description

  The `double` function typecasts an object `x` to double precision. For example, if `x` is an array of integers, an array of double types will be returned. If an object cannot be converted to `Double_Type`, a type-mismatch error will result.

Notes

  The `double` function is equivalent to the typecast operation

  > `

  >          typecast (x, Double_Type)

  > `

  To convert a string to a double precision number, use `atoi` function.
See Also

  `typecast, atoi, int`

## 9.7 int

Synopsis

  Typecast an object to an integer

Usage

  `int (s)`

Description

  This function performs a typecast of `s` from its data type to an object of `Integer_Type`. If `s` is a string, it returns returns the ascii value value of the first character of the string `s`. If `s` is `Double_Type`, `int` truncates the number to an integer and returns it.

Example

  `int` can be used to convert single character strings to integers. As an example, the intrinsic function `isdigit` may be defined as

  > `

  >         define isdigit (s)
  >         {
  >           if ((int (s) >= '0') and (int (s) <= '9')) return 1;
  >           return 0;
  >         }

  > `

Notes

  This function is equalent to `typecast (s, Integer_Type)`;

See Also

  `typecast, double, integer, char, isdigit`

## 9.8 integer

Synopsis

  Convert a string to an integer

Usage

  `Integer_Type integer (String_Type s)`

Description

  The `integer` function converts a string representation of an integer back to an integer. If the string does not form a valid integer, a type-mismatch error will be generated.

Example

  `integer ("1234")` returns the integer value `1234`.

Notes

  This function operates only on strings and is not the same as the more general `typecast` operator.

See Also

  `typecast, _slang_guess_type, string, sprintf, char`

## 9.9 isdigit

Synopsis

  Tests for a decimal digit character

Usage

  `Integer_Type isdigit (String_Type s)`

Description

  This function returns a non-zero value if the first character in the string `s` is a digit; otherwise, it returns zero.

Example

  A simple, user defined implementation of `isdigit` is

  > `

  >         define isdigit (s)
  >         {
  >            return ((s[0] <= '9') and (s[0]  >= '0'));
  >         }

  > `

  However, the intrinsic function `isdigit` executes many times faster than the equivalent representation defined above.
Notes

  Unlike the C function with the same name, the S-lang function takes a string argument.

See Also

  `int, integer`

## 9.10 string

Synopsis

  Convert an object to a string representation.

Usage

  `Integer_Type string (obj)`

Description

  The `string` function may be used to convert an object `obj` of any type to a string representation. For example, `string(12.34)` returns `"12.34"`.

Example

  > `

  >          define print_anything (anything)
  >          {
  >             message (string (anything));
  >          }

  > `

Notes

  This function is not the same as typecasting to a `String_Type` using the `typecast` function.

See Also

  `typecast, sprintf, integer, char`

## 9.11 tolower

Synopsis

  Convert a character to lowercase.

Usage

  `Integer_Type lower (Integer_Type ch)`

Description

  This function takes an integer `ch` and returns its lowercase equivalent.

See Also

  `toupper, strup, strlow, int, char, define_case`

## 9.12 toupper

Synopsis

  Convert a character to uppercase.

Usage

  `Integer_Type toupper (Integer_Type ch)`

Description

  This function takes an integer `ch` and returns its uppercase equivalent.

See Also

  `tolower, strup, strlow, int, char, define_case`

## 9.13 typecast

Synopsis

  Convert an object from one data type to another.

Usage

  `typecast (x, new_type)`

Description

  The `typecast` function performs a generic typecast operation on `x` to convert it to `new_type`. If `x` represents an array, the function will attempt to convert all elements of `x` to `new_type`. Not all objects can be converted and a type-mismatch error will result upon failure.

Example

  > `

  >         define to_complex (x)
  >         {
  >            return typecast (x, Complex_Type);
  >         }

  > `

  defines a function that converts its argument, `x` to a complex number.
See Also

  `int, double, typeof`

## 9.14 typeof

Synopsis

  Get the data type of an object.

Usage

  `DataType_Type typeof (x)`

Description

  This function returns the data type of `x`.

Example

  > `

  >       if (Integer_Type == typeof (x)) message ("x is an integer");

  > `

See Also

  `_typeof, is_struct_type, array_info, _slang_guess_type, typecast`

Next Previous Contents