Conversions

General

Explicit type conversion is performed using the cast operator. If an operation or language construct expects operand of one type and a value of another type is given, implicit (automatic) conversion will be performed. Same will happen with most internal functions, though some functions may do different things depending on argument type and thus would not perform the conversion.

If an expression is converted to its own type, the type and value of the result are the same as the type and value of the expression.

Conversions to resource and null types can not be performed.

Converting to Boolean Type

The [result type] (http://www.php.net/manual/en/language.types.boolean.php#language.types.boolean.casting) is bool.

If the source type is int or float, then if the source value tests equal to 0, the result value is FALSE; otherwise, the result value is TRUE.

If the source value is NULL, the result value is FALSE.

If the source is an empty string or the string “0”, the result value is FALSE; otherwise, the result value is TRUE.

If the source is an array with zero elements, the result value is FALSE; otherwise, the result value is TRUE.

If the source is an object, the result value is TRUE.

If the source is a resource, the result value is TRUE.

The library function boolval allows values to be converted to bool.

Converting to Integer Type

The result type is int.

If the source type is bool, then if the source value is FALSE, the result value is 0; otherwise, the result value is 1.

If the source type is float, for the values INF, -INF, and NAN, the result value is zero. For all other values, if the precision can be preserved (that is, the float is within the range of an integer), the fractional part is rounded towards zero. If the precision cannot be preserved, the following conversion algorithm is used, where X is defined as two to the power of the number of bits in an integer (for example, 2 to the power of 32, i.e. 4294967296):

  1. We take the floating point remainder (wherein the remainder has the same sign as the dividend) of dividing the float by X, rounded towards zero.
  2. If the remainder is less than zero, it is rounded towards infinity and X is added.
  3. This result is converted to an unsigned integer.
  4. This result is converted to a signed integer by treating the unsigned integer as a two’s complement representation of the signed integer.

Implementations may implement this conversion differently (for example, on some architectures there may be hardware support for this specific conversion mode) so long as the result is the same.

If the source value is NULL, the result value is 0.

If the source is a numeric string or leading-numeric string having integer format, if the precision can be preserved the result value is that string’s integer value; otherwise, the result is undefined. If the source is a numeric string or leading-numeric string having floating-point format, the string’s floating-point value is treated as described above for a conversion from float. The trailing non-numeric characters in leading-numeric strings are ignored. For any other string, the result value is 0.

If the source is an array with zero elements, the result value is 0; otherwise, the result value is 1.

If the source is an object, if the class defines a conversion function, the result is determined by that function (this is currently available only to internal classes). If not, the conversion is invalid, the result is assumed to be 1 and a non-fatal error is produced.

If the source is a resource, the result is the resource’s unique ID.

The library function intval allows values to be converted to int.

Converting to Floating-Point Type

The result type is float.

If the source type is int, if the precision can be preserved the result value is the closest approximation to the source value; otherwise, the result is undefined.

If the source is a numeric string or leading-numeric string having integer format, the string’s integer value is treated as described above for a conversion from int. If the source is a numeric string or leading-numeric string having floating-point format, the result value is the closest approximation to the string’s floating-point value. The trailing non-numeric characters in leading-numeric strings are ignored. For any other string, the result value is 0.

If the source is an object, if the class defines a conversion function, the result is determined by that function (this is currently available only to internal classes). If not, the conversion is invalid, the result is assumed to be 1.0 and a non-fatal error is produced.

For sources of all other types, the conversion result is obtained by first converting the source value to int and then to float.

The library function floatval allows values to be converted to float.

Converting to String Type

The result type is string.

If the source type is bool, then if the source value is FALSE, the result value is the empty string; otherwise, the result value is “1”.

If the source type is int or float, then the result value is a string containing the textual representation of the source value (as specified by the library function sprintf).

If the source value is NULL, the result value is the empty string.

If the source is an array, the conversion is invalid. The result value is the string “Array” and a non-fatal error is produced.

If the source is an object, then if that object’s class has a __toString method, the result value is the string returned by that method; otherwise, the conversion is invalid and a fatal error is produced.

If the source is a resource, the result value is an implementation-defined string.

The library function strval allows values to be converted to string.

Converting to Array Type

The result type is array.

If the source value is NULL, the result value is an array of zero elements.

If the source type is scalar or resource and it is non-NULL, the result value is an array of one element under the key 0 whose value is that of the source.

If the source is an object, the result is an array of zero or more elements, where the elements are key/value pairs corresponding to the object‘s instance properties. The order of insertion of the elements into the array is the lexical order of the instance properties in the class-member-declarations list.

For public instance properties, the keys of the array elements would be the same as the property name.

The key for a private instance property has the form “\0class\0name“, where the class is the class name, and the name is the property name.

The key for a protected instance property has the form “\0*\0name“, where name is that of the property.

The value for each key is that from the corresponding property, or NULL if the property was not initialized.

Converting to Object Type

The result type is object.

If the source has any type other than object, the result is an instance of the predefined class stdClass. If the value of the source is NULL, the instance is empty. If the value of the source has a scalar type and is non-NULL, or is a resource, the instance contains a public property called scalar whose value is that of the source. If the value of the source is an array, the instance contains a set of public properties whose names and values are those of the corresponding key/value pairs in the source. The order of the properties is the order of insertion of the source’s elements.