Difference between revisions of "@"
(add Template:Symbols) |
m (ordinal numbers in syntaxhighlight) |
||
| Line 9: | Line 9: | ||
Here some example to demonstrate, what produces with untyped pointers valid and functional code, but semantically outputs an erroneous result: | Here some example to demonstrate, what produces with untyped pointers valid and functional code, but semantically outputs an erroneous result: | ||
| − | <syntaxhighlight lang="pascal" line | + | <syntaxhighlight lang="pascal" line highlight="12">program untypedAddressDemo(input, output, stderr); |
procedure incrementIntByRef(const ref: PByte); | procedure incrementIntByRef(const ref: PByte); | ||
Revision as of 17:42, 11 April 2018
│
English (en) │
suomi (fi) │
français (fr) │
русский (ru) │
The address operator @ returns the address of a variable, procedure or function.
Normally, the value @ returns is an untyped pointer.
If you are handling pointers a lot, and want to mitigate issues with passing references of wrong type's target, you have use the directive {$typedaddress on}.
Here some example to demonstrate, what produces with untyped pointers valid and functional code, but semantically outputs an erroneous result:
1program untypedAddressDemo(input, output, stderr);
2
3procedure incrementIntByRef(const ref: PByte);
4begin
5 inc(ref^);
6end;
7
8var
9 foo: integer;
10begin
11 foo := -1;
12 incrementIntByRef(@foo);
13 writeLn(foo);
14end.
It was intended, that 0 (zero) gets printed, but the program prints -256 instead.
With {$typedaddress on} compilation fails with an incompatible type error.
You usually want the latter behavior (compile-time failure) instead of wasting time with hours of debugging.
read more
| single characters |
|
| character pairs |
|
