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digitalmars.D.learn - Unexpected result with -betterC

reply DLearner <bmqazwsx123 gmail.com> writes:
The two fragments below compiled and ran as expected using dmd 
-betterC under Windows.

```
    string Scrn = "OPO NAM='DspVar1' POS='1,1' 
VAR=('IntVar1','I');E";


    printf("\nWR_Createtest entered.\n");


    OpStructFstPtr = WR_CreateFormatFile(Scrn);

```

```
OpStruct* WR_CreateFormatFile(string parm_Format) {

    import core.stdc.stdio: printf;
    import core.stdc.stdlib: malloc;


    OpStruct* FstOpStructPtr;


    if (parm_Format[0..3] == "OPO"[0..3]) {
       printf("OPO Found.\n");
    } else {
       printf("OPO NOT Found.\n");
    }

    if (parm_Format[$-1..$] == "E"[0..1]) {
       printf("E Found.\n");
    } else {
       printf("E NOT Found.\n");
    }

```

However, the docs say dynamic arrays are not allowed with 
betterC, and 'string' implies a dynamic array.
So I expected DMD to complain that my code was invalid.

Any ideas?
Nov 03 2024
next sibling parent reply monkyyy <crazymonkyyy gmail.com> writes:
On Sunday, 3 November 2024 at 19:00:33 UTC, DLearner wrote:

 The two fragments below compiled and ran as expected using dmd 
 -betterC under Windows.

 ```
    string Scrn = "OPO NAM='DspVar1' POS='1,1' 
 VAR=('IntVar1','I');E";


    printf("\nWR_Createtest entered.\n");


    OpStructFstPtr = WR_CreateFormatFile(Scrn);

 ```

 ```
 OpStruct* WR_CreateFormatFile(string parm_Format) {

    import core.stdc.stdio: printf;
    import core.stdc.stdlib: malloc;


    OpStruct* FstOpStructPtr;


    if (parm_Format[0..3] == "OPO"[0..3]) {
       printf("OPO Found.\n");
    } else {
       printf("OPO NOT Found.\n");
    }

    if (parm_Format[$-1..$] == "E"[0..1]) {
       printf("E Found.\n");
    } else {
       printf("E NOT Found.\n");
    }

 ```

 However, the docs say dynamic arrays are not allowed with 
 betterC, and 'string' implies a dynamic array.
 So I expected DMD to complain that my code was invalid.

 Any ideas?


Id expect this to fail, but nothing I see in yours

```d
string foo="foo";
foo~="bar";
```

[]'s are both slices and dynamic arrays depending on use, theres 
a debate about that decision(im of the opinion a `[?]` should be 
a dynamic array and clean up the api), but the current situation 
will only break on appends
Nov 03 2024
parent reply DLearner <bmqazwsx123 gmail.com> writes:
On Sunday, 3 November 2024 at 19:47:31 UTC, monkyyy wrote:
[...]

 Id expect this to fail, but nothing I see in yours

 ```d
 string foo="foo";
 foo~="bar";
 ```

 []'s are both slices and dynamic arrays depending on use, 
 theres a debate about that decision(im of the opinion a `[?]` 
 should be a dynamic array and clean up the api), but the 
 current situation will only break on appends


Surely the line:

```
    string Scrn = "OPO NAM='DspVar1' POS='1,1' 
VAR=('IntVar1','I');E";
```
creates, by the definition of 'string', a dynamic array?
Nov 03 2024
next sibling parent Juraj <junk vec4.xyz> writes:
On Sunday, 3 November 2024 at 20:04:19 UTC, DLearner wrote:

 On Sunday, 3 November 2024 at 19:47:31 UTC, monkyyy wrote:
 [...]

 Id expect this to fail, but nothing I see in yours

 ```d
 string foo="foo";
 foo~="bar";
 ```

 []'s are both slices and dynamic arrays depending on use, 
 theres a debate about that decision(im of the opinion a `[?]` 
 should be a dynamic array and clean up the api), but the 
 current situation will only break on appends


 Surely the line:

 ```
    string Scrn = "OPO NAM='DspVar1' POS='1,1' 
 VAR=('IntVar1','I');E";
 ```
 creates, by the definition of 'string', a dynamic array?


By default, a string literal is typed as a dynamic array, but the 
element count is known at compile time. So all string literals 
can be implicitly converted to an immutable static array. 
[spec](https://dlang.org/spec/expression.html#string_literals)
Nov 03 2024
prev sibling parent monkyyy <crazymonkyyy gmail.com> writes:
On Sunday, 3 November 2024 at 20:04:19 UTC, DLearner wrote:

 
 Surely the line:

 ```
    string Scrn = "OPO NAM='DspVar1' POS='1,1' 
 VAR=('IntVar1','I');E";
 ```
 creates, by the definition of 'string', a dynamic array?


I believe thats stored in the binary
Nov 03 2024
prev sibling parent Paul Backus <snarwin gmail.com> writes:
On Sunday, 3 November 2024 at 19:00:33 UTC, DLearner wrote:

 However, the docs say dynamic arrays are not allowed with 
 betterC, and 'string' implies a dynamic array.
 So I expected DMD to complain that my code was invalid.

 Any ideas?


The docs are wrong. Dynamic arrays themselves are allowed; you're 
just not allowed to perform any *operations* on them that would 
cause memory allocation.

This includes, for example,

- concatenating two dynamic arrays with the `~` operator.
- appending to a dynamic array with the `~=` operator.
- extending a dynamic array by assigning to its `.length` 
property.
- copying a dynamic array using the built-in `.dup` method.
Nov 03 2024