Are delphi variables initialized with a value by default?

Solution 1:

Yes, this is the documented behaviour:

• Object fields are always initialized to 0, 0.0, '', False, nil or whatever applies.

• Global variables are always initialized to 0 etc as well;

• Local reference-counted* variables are always initialized to nil or '';

• Local non reference-counted* variables are uninitialized so you have to assign a value before you can use them.

I remember that Barry Kelly somewhere wrote a definition for "reference-counted", but cannot find it any more, so this should do in the meantime:

reference-counted == that are reference-counted themselves, or directly or indirectly contain fields (for records) or elements (for arrays) that are reference-counted like: string, variant, interface or dynamic array or static array containing such types.

Notes:

• record itself is not enough to become reference-counted
• I have not tried this with generics yet

Solution 2:

Global variables that don't have an explicit initializer are allocated in the BSS section in the executable. They don't actually take up any space in the EXE; the BSS section is a special section that the OS allocates and clears to zero. On other operating systems, there are similar mechanisms.

You can depend on global variables being zero-initialized.

Solution 3:

Class fields are default zero. This is documented so you can rely on it. Local stack varaiables are undefined unless string or interface, these are set to zero.