On Thursday, 14 September 2023 at 14:21:09 UTC, Vino wrote:
Questions:1
```
char[] invalid = (cast(char*)malloc(char.sizeof *
length))[0..length];
```
The above statement allocate memory for char type and the size
of the allocated memory is char.sizeof * length so what is the
use of this "[0..length]";
The difference between a `char*` and a `char[]` is that the
`char[]` includes both the pointer and the length in the same
variable. The slicing operator `[0 .. length]` is used to combine
the pointer and the length into a single `char[]` variable.
Strictly speaking, you don't *have* to do this--you could leave
the pointer and the length in separate variables, and the program
would still work. Most D programmers prefer to combine them
because it's more convenient and less error-prone (for example,
it makes it much harder to accidentally use the wrong length).
Question:2
```
char[]* invalidptr = &invalid;
```
Is this the right way to create a array pointer.
It depends on what you mean by "array pointer".
A `char[]` contains a pointer and a length. A `char[]*` is a
pointer to a thing that contains a pointer and a length. In order
to get from a `char[]*` to the actual `char` data, you have to
follow *two* pointers. In that sense, you can think of `char[]*`
in D as similar to `char**` in C.
Question: 3
```
ST1: char[] invalid = (cast(char*)malloc(char.sizeof *
length))[0..length];
ST2: char[]* invalid = (cast(char*)malloc(char.sizeof *
length))[0..length];
```
What is the difference between the above to statement.
The first statement is valid code and the second one isn't.
Question: 4
Who do we free the memory allocated.
Code:
[...]
In order to ensure that the memory is freed correctly even when
an exception is thrown, you can use a [`try`/`finally` block.][1]
char[] a = (cast(char*) malloc(char.sizeof * length))[0 ..
length];
try {
doSomethingWith(a);
} finally {
free(a.ptr);
}
However, this by itself will not fix the code in your example
because it has another serious mistake: it does not initialize
the memory allocated by `malloc`. Attempting to read from
uninitialized memory results in [undefined behavior][2], which
may cause your program to crash or behave unpredictably.
[1]: http://ddili.org/ders/d.en/exceptions.html#ix_exceptions.try
[2]: https://c-faq.com/ansi/undef.html
