• areYouSureAboutThat (16/16) Jan 05 2023 I was playing around with betterC, when I discovered, that if i
• areYouSureAboutThat (14/14) Jan 05 2023 On Thursday, 5 January 2023 at 09:10:00 UTC, areYouSureAboutThat
• Mathias LANG (3/6) Jan 05 2023 This is bounds checking happening.
• Richard (Rikki) Andrew Cattermole (5/11) Jan 05 2023 Looks like an exception to me, which is what the default for bounds
• Tejas (27/43) Jan 05 2023 Works on run.dlang.io for me:
• tsbockman (23/27) Jan 05 2023 Note that whether bounds checking is performed depends on

areYouSureAboutThat <areYouSureAboutThat gmail.com> writes:

I was playing around with betterC, when I discovered, that if i 
accidently forget to provide -betterC to the compiler, it will 
still compile this, but, there will be no runtime bounds checking 
occuring.

My question is: why is there no bounds checking occurring if I 
forget to use -betterC?

module test;

extern(C) void main()
{
     import core.stdc.stdio : printf;


     int[5] arr = [ 0, 1, 2, 3, 4];

     for (int i = 0; i < 10; i++) // oops!
     {
         printf("%d\n", arr[i]);
     }
}

areYouSureAboutThat <areYouSureAboutThat gmail.com> writes:

On Thursday, 5 January 2023 at 09:10:00 UTC, areYouSureAboutThat 
wrote:

btw. the output (when you forget to use -betterC):

0
1
2
3
4
src/rt/dwarfeh.d:330: uncaught exception reached top of stack
This might happen if you're missing a top level catch in your 
fiber or signal handler
core.exception.ArrayIndexError test.d(25): index [5] exceeds 
array of length 5
Aborted (core dumped)

Mathias LANG <geod24 gmail.com> writes:

On Thursday, 5 January 2023 at 09:17:28 UTC, areYouSureAboutThat 
wrote:
 core.exception.ArrayIndexError test.d(25): index [5] exceeds 
 array of length 5
 Aborted (core dumped)

This is bounds checking happening.

"Richard (Rikki) Andrew Cattermole" <richard cattermole.co.nz> writes:

On 05/01/2023 10:17 PM, areYouSureAboutThat wrote:
 src/rt/dwarfeh.d:330: uncaught exception reached top of stack
 This might happen if you're missing a top level catch in your fiber or 
 signal handler
 core.exception.ArrayIndexError test.d(25): index [5] exceeds array of 
 length 5
 Aborted (core dumped)

Looks like an exception to me, which is what the default for bounds 
check on error will do.

Because you are not using the druntime entry point, its not being caught 
and made to look nice to you.

Tejas <notrealemail gmail.com> writes:

On Thursday, 5 January 2023 at 09:10:00 UTC, areYouSureAboutThat 
wrote:
 I was playing around with betterC, when I discovered, that if i 
 accidently forget to provide -betterC to the compiler, it will 
 still compile this, but, there will be no runtime bounds 
 checking occuring.

 My question is: why is there no bounds checking occurring if I 
 forget to use -betterC?

 module test;

 extern(C) void main()
 {
     import core.stdc.stdio : printf;


     int[5] arr = [ 0, 1, 2, 3, 4];

     for (int i = 0; i < 10; i++) // oops!
     {
         printf("%d\n", arr[i]);
     }
 }

Works on run.dlang.io for me:
```sh
0
1
2
3
4
dmd_runJFfSJW: onlineapp.d:12: Assertion 'array index out of 
bounds' failed.
Error: program killed by signal 6
```

On my personal ldc 1.27.1:
```sh
(base) [tejasgarhewal fedora ~]$ ldc2 -betterC -run ./D/oob.d
0
1
2
3
4
oob-06265c: ./D/oob.d:9: Assertion 'array overflow' failed.
Error: /tmp/oob-06265c failed with status: -2
        message: Aborted (core dumped)
Error: program received signal 2 (Interrupt)
(base) [tejasgarhewal fedora ~]$
```

tsbockman <thomas.bockman gmail.com> writes:

On Thursday, 5 January 2023 at 09:10:00 UTC, areYouSureAboutThat 
wrote:
 My question is: why is there no bounds checking occurring if I 
 forget to use -betterC?

 module test;

 extern(C) void main()

Note that whether bounds checking is performed depends on 
[compiler 
switches](https://dlang.org/dmd-windows.html#switch-boundscheck), 
and that there is a mode where ` safe` functions are checked, but 
` system` functions (which your `main` appears to be) are not. 
This mode is the default for `-release` builds:
```
-boundscheck=[on|safeonly|off ]
Controls if bounds checking is enabled.
     on: Bounds checks are enabled for all code. This is the 
default.

     safeonly: Bounds checks are enabled only in  safe code. This 
is the default for -release builds.

     off: Bounds checks are disabled completely (even in  safe 
code). This option should be used with caution and as a last 
resort to improve performance. Confirm turning off  safe bounds 
checks is worthwhile by benchmarking.
```
So, if you want bounds checking, make  sure you either have 
`-boundscheck=on`, or use an ` safe` function together with 
`-boundscheck=safeonly`.