What are unaligned typecasts in Pascal expressions?

In the Pascal programming language, typecasting enables us to assign values to variables and expressions that are not compatible with the variable's original data type, virtually overriding Pascal's strong typing capabilities.

An unaligned typecast is a special type of typecast. Actually, this is not a true typecast but in such a scenario, the compiler is informed that the expression may be misaligned, or in other words, it's not on an aligned memory address.

By typecasting an expression with the unaligned keyword, the compiler is instructed to access the data byte by byte.

Let's take a deeper look at the following example to improve our understanding of this topic.

Code example

The following example shows how to fetch an unaligned variable:

program hello;
Var
  v_array : packed Array[1..10] of Byte;
  v : LongInt;
 begin
  writeln('Start...');
  For v:=1 to 10 do
      v_array[v]:=v;
      
  writeln('v = ', (PInteger(Unaligned(@v_array[3]))^));
  writeLn('The Binary representation of the byte in string format = ' , binStr(v_array[3], 8));
  writeln('End...');    
end.

Code explanation

  • Line 1: We refer to the program header. It is used for backward compatibility and is ignored by the compiler.

  • Line 4: We declare a packed array called v_array of 10 bytes.

  • Line 5: We declare a LongInt variable v.

  • Lines 8–9: We iterate across a sequence ranging from 1 to 10 and fill out the array v_array with the sequence number.

  • Line 11: Using the @ operator, we get the address of the third element of the array v_array. With PInteger, we convert the typed pointer returned by the @ operator to an integer type and print out the result.

  • Line 13: Using the function binStr, we extract and print out a string that shows the binary representation of the third element of the array v_array.

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