lang • read

READ

Variable = READ [ # Stream ] AS Datatype Variable = READ [ # Stream , ] Length

Reading a specific datatype

The first syntax reads the stream Stream as binary data whose type is specified by the Datatype argument. The binary representation is the one used by the WRITE instruction.

If the stream is not specified, then the standard input is used.

The returned datatype can be one of the following: NULL, Boolean, Byte, Short, Integer, Long, Pointer, Single, Float, Date, String, Variant, any Array, Collection or structure.

When reading a string, the length of the string must precede the string contents in the stream data.

See Binary Data Representation for more information.

Since 3.15
If the Stream.NullTerminatedString property is set, then the length of the string is not read, and the string is read until a null byte is encountered.

If the stream contents cannot be interpreted, an error is raised.

This instruction uses the byte order of the stream to read the data.

Reading any object

Since 3.15

Any object can be unserialized, provided that its class implements the _read special method.

If the object has been previously serialized to the stream in the right way, it is rebuild by calling its constructor with no argument, and then the _read method is called.

You read the object by using one of the following syntax:

Object = READ # Stream As ObjectClass Object = READ # Stream As Object Object = READ # Stream As Variant

If you read the object by using 'As Variant' or 'As Object', you have to have written it by using 'As Variant' or 'As Object'.

Because in that case the needed object class name is written to the stream. Otherwise the READ instruction does not have the class name needed to instanciate the object.

Reading the contents of a string

The second syntax reads from the stream Stream a number of bytes specified by the Length argument, and returns it as a string.

If Length is negative, then at most (- Length) bytes are read until the end of the stream.

If the stream is not specified, then the standard input is used.

Compatibility with Gambas 2

WRITE #Stream, Expression writes the binary form of Expression in Gambas 2.0. In Gambas 3.0 it writes Expression as a string.

So you HAVE to check all your WRITE instructions when converting a Gambas project from 2.0 to 3.0, and specified AS Datatype when need.

By default, the compiler supports the old READ syntax, and the old WRITE syntax as it is compatible.

If you want to detect where you should rewrite your READ / WRITE syntax, you can compile your project by hand with the "--no-old-read-write-syntax" flag. Then the Length argument of WRITE becomes mandatory if the second syntax is used.

Using a Pointer as a stream is not possible anymore. Create a memory stream with the OPEN MEMORY instruction instead.

See also