On Friday, 15 September 2023 at 16:55:34 UTC, Vino wrote:
On Friday, 15 September 2023 at 15:27:00 UTC, Vino wrote:
On Friday, 15 September 2023 at 02:25:09 UTC, Joe wrote:
On Thursday, 14 September 2023 at 14:21:09 UTC, Vino wrote:
[...]
A pointer is a type that points to something. It's literally
that simple. Every piece of data and code exist somewhere in
memory. Every piece of memory has an address. The address is
what a pointer contains. Sometimes we want a type that is the
address itself rather than a value/number.
[...]
Hi Joe,
Thank you very much for the explanation can you please correct
me if my understanding is incorrect
```
byte[] z; // Creates an array of bytes. That is, the compiler
will create a pointer to an array of memory and track it's
length and deal with memory allocation and all that.
```
If we use the above method then :
The compiler takes care of initilizing the array and free the
memory after the usage.
And this is the recommended method.
```
We can use a pointer as an array also, this is the "old school
way of creating arrays".
int qlen = 5;
int* q = cast(int*)malloc(int.sizeof*qlen);
```
If we use the above method then :
We need to manual initilize the array.
Ensure that the memory is freed after the usage using
try/final block.
By default the memory allocation for arrays in D is based on
GC (expect for std.array containers) if we want to
reduce/avoid GC then we need to use the old school way of
creating the arrays.
In case of using the old school ways then can you guide me
what is wrong in my earlier code that I am getting the below
error and how do I correct the same.
Error
```
Invalid Name passed: /T&name
double free or corruption (out)
Error: program killed by signal 6
```
Hi All,
At last was able to resolve the issue, but not sure
whether this is the reight solution.
Code:
```
import std.stdio: writeln;
import std.exception: enforce;
import std.range: empty;
import std.format: format;
auto ref testNames(in string[] names) {
enforce(!empty(names), "Names cannot be Empty or Null");
import core.stdc.stdlib;
import std.algorithm: any, canFind;
string[] _names;
size_t len = 19;
char[] invalid = (cast(char*)malloc(char.sizeof *
len))[0..len];
invalid[0 ..len] = 0; //Array Initlization
try {
version(Posix) {
invalid =
['\'','\"',':',';','*','&','/','[',']','-','+','$','#','<','>','{','}','(',')'];
}
foreach(i; names.dup) {
auto result = i.any!(a => invalid.canFind(a));
if(result) { throw new Exception("Invalid Name
passed: %s".format(i)); }
else {_names = names.dup; return _names; }
}
} catch(Exception e) { writeln(e.msg); }
finally { invalid = null; free(invalid.ptr); } //
added invalid = null resolved the issue
return _names;
}
void main () {
writeln(testNames(["/T&name"]));
}
From,
Vino
char[] invalid = (cast(char*)malloc(char.sizeof * len))[0..len];
This is not the way to go about it. You are mixing "pointer
arrays" with "arrays".
You are creating a pointer array then turning that in to an
array. There is no need to do that. Basically you are copying
what the compiler already does for you.
When you are using arrays([] language) you don't have to worry
about anything. Just use them as arrays directly and let the
compiler deal with memory management. The entire point of
"managed arrays" is to avoid having to manually deal with memory
which can cause problems if one is not careful.
Of course you have to make sure your array used used correctly
but that should be obvious.
char[] invalid = (cast(char*)malloc(char.sizeof * len))[0..len];
is exactly the same as
char[] invalid. EXCEPT that you've forced it to be initialized
with a length of len and went from D in to C then back to D just
to create an array. You are making it much more complex than it
needs to be. There are good tutorials on D arrays that you should
look over. You will see how easy they are.
You could just do char[] invalid = new char[](len); for the same
effect but is nicer. New understands char, malloc only
understands bytes. You should not use malloc in D unless you
explicitly know you need to use it. Malloc is primitive memory
management.
When you use D's symantics for arrays it is much easier... which
is the entire point. You don't even need to free the arrays. D
knows they are local variable sand will free them when out of
scope. It will grow them when they need to grow, etc.
invalid = null; free(invalid.ptr);
That does nothing. you set invalid.ptr to null and are freeing
null so you are not freeing the array.
You don't have to though, the array will be free out of scope(not
in final though so exceptions could cause memory leak) because it
is a D array.
Do not use free or malloc in your D programs until you understand
D arrays. You are making it much harder on yourself. The entire
point of D arrays is to be simpler and take all the trouble out
of pointer arrays.
// This creates an array of chars of length 6(it can change if we
append)
char[] A = new char[](6);
A[0..$] = 'a'; // initializes all entries to 'a'
writeln(A[4]); // shows that the 5th entry is 'a'
We don't have to worry about freeing up the array, D will do it
for us.
https://dlang.org/spec/arrays.html
