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doc: add section about new/dispose/newOrNil

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slederer 2025-09-19 21:58:44 +02:00
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doc/pascalprogramming.md
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@ -103,6 +103,16 @@ Tridora-Pascal only supports the _break_ statement at the moment.
The _exit_ statement can be used to exit the current procedure or function. If it is a function, the return value of the function is undefined if _exit_ is The _exit_ statement can be used to exit the current procedure or function. If it is a function, the return value of the function is undefined if _exit_ is
used before a return value is assigned. used before a return value is assigned.
## Dynamic Memory Allocation
Memory allocation generally works as expected with the *new* and *dispose* special procedures. The variant of *new* with two parameters that is specified in Wirth Pascal is not supported (partial allocation of a variant record). Instead, there is a variant of *new* that has a second parameter for allocating strings (see above).
If heap allocation fails, *new* does not return and instead causes a runtime error. To avoid this, a different special procedure called *newOrNil* can be used. This procedure sets the pointer
variable to *niL* if heap allocation fails.
The function *MemAvail* returns the number of free bytes on the heap. It does not guarantee that this amount of memory can be allocated with *new*, because heap space can be fragmented.
The function *MaxAvail*, which exists in some versions of Turbo Pascal and returns the size of the largest contiguous block of available heap memory, is not (yet) implemented.
## I/O ## I/O
I/O handling in Tridora Pascal is mostly compatible with other Pascal dialects when reading/writing simple variables from/to the console. There are big differences when opening/reading/writing files explicitly. I/O handling in Tridora Pascal is mostly compatible with other Pascal dialects when reading/writing simple variables from/to the console. There are big differences when opening/reading/writing files explicitly.