Debugger Option to View Pointer as Array.

[skl131313]

For dynamically allocated arrays are simply represented as a pointer, which has no other indicator that it is an array. It would be nice to have a feature to view a pointer as an array as to view more than simply the first element of the array. In the "variables" tab and also when previewing a variable by hovering over it while debugging.

[pieandcakes]

@sprinkle131313 with our 0.9.3 release, we updated to enable gdb's pretty-printing in launch.json as a default. This should resolve this issue. Please comment/reopen with more information if it doesn't

[kevinmoran]

It would make a HUGE difference if I could type "some_pointer,x" in the watch window to view some_pointer as an array with x elements.

As it stands I have to use LLDB's memory read syntax, which I constantly have to google and sometimes doesn't seem to work. I've actually resorted to printf debugging for large arrays the last few days. Could we please reopen this issue or can I open another to look into something like that being implemented? It's my number 1 gripe with VSCode debugging at the moment (one of my only gripes).

[pieandcakes]

@kevinmoran We have updated our version of the shipped LLDB to allow lldb's python pretty printer to work. Your other option is to look at our Natvis visualizer option. The commands you are putting in the watch window are sent to the underlying debugger to evaluate.

[kevinmoran]

Thanks for getting back to me, have a decent solution now. For anyone who found themselves here Googling this same problem, you can put this in the watch window:
*(int(*)[10])some_pointer
to print "some_pointer" as a 10-element array of type int.

Would still argue that having a simpler solution is a basic debugger feature that should be added, this is way too much syntax/thinking/remembering to do something basic. Debuggers should get out of your way, not challenge you when you're trying to think about your actual code.

[salda]

I agree with kevinmoran, that retyping the pointer is too complicated by hand and should be done by debugger.

[pieandcakes]

@salda We will take it as a feature request but the underlying debugger is lldb or gdb so the change would need to happen in the debugger itself and not the extension.

[noobling]

#172 (comment)
Has this feature been added for pointer to pointers? e.g. char**

[creikey]

@noobling Yes, I am having trouble printing pointer to pointers as well

[giuscri]

For anyone who found themselves here Googling this same problem, you can put this in the watch window:
*(int(*)[10])some_pointer
to print "some_pointer" as a 10-element array of type int.

or, even simpler: *some_pointer@3. Bonus point, check out *argv@argc!

[ghost]

If you do what @giuscri suggests and put a breakpoint in the function that computes the pointer, the watch will stall indefinitely and cannot be deleted (Windows 10)

eg *tests()@4 will stall if there is a breakpoint in tests(), a function which returns a pointer to a list of test results.

reloading the window after this happens seems to fix it.

[brunohenriquepj]

or, even simpler: *some_pointer@3. Bonus point, check out *argv@argc!

If you have the array length in a variable (e.g., length) you can do this: *some_pointer@length

[teichert]

Thanks @giuscri!
If anyone else was wanting to use *s@strlen(s) to display a c-string without typing in the length, it turns out that the thing to do in gdb is to use: $_strlen. So if you have a c-string, s, you can display the underlying char array by using the following as a watch expression (the + 1 is for showing the terminating null char): *s@$_strlen(s)+1

[tuket]

For anyone who found themselves here Googling this same problem, you can put this in the watch window:
*(int(*)[10])some_pointer
to print "some_pointer" as a 10-element array of type int.

or, even simpler: *some_pointer@3. Bonus point, check out *argv@argc!

Looks like this doesn't work anymore?

[Gaming32]

For anyone who found themselves here Googling this same problem, you can put this in the watch window:
*(int(*)[10])some_pointer
to print "some_pointer" as a 10-element array of type int.

or, even simpler: *some_pointer@3. Bonus point, check out *argv@argc!

Looks like this doesn't work anymore?

It works fine for me

[tripathics]

or, even simpler: *some_pointer@3. Bonus point, check out *argv@argc!

If you have the array length in a variable (e.g., length) you can do this: *some_pointer@length

Thank you @brunohenriquepj , what would I do without you.. I tried all the suggestions above your answers, none of them worked on my linux machine. But You helped alot.. Will remember this

*some_pointer@length

BTW I have just started coding with C.

[JJJohan]

For anyone who found themselves here Googling this same problem, you can put this in the watch window:
*(int(*)[10])some_pointer
to print "some_pointer" as a 10-element array of type int.

or, even simpler: *some_pointer@3. Bonus point, check out *argv@argc!

Looks like this doesn't work anymore?

For MSVC (i.e. when using cppvsdbg instead of cppdbg) substitute the @ symbol with a comma, and omit the dereferencing, i.e. i.e. some_pointer,10. Only just figured this out myself!

[tripathics]

For anyone who found themselves here Googling this same problem, you can put this in the watch window:
*(int(*)[10])some_pointer
to print "some_pointer" as a 10-element array of type int.

or, even simpler: *some_pointer@3. Bonus point, check out *argv@argc!

Looks like this doesn't work anymore?

For MSVC (i.e. when using cppvsdbg instead of cppdbg) substitute the @ symbol with a comma, and omit the dereferencing, i.e. i.e. some_pointer,10. Only just figured this out myself!

@JJJohan Can I ask what is cppvsdbg? And is it available on Linux?

[JJJohan]

@JJJohan Can I ask what is cppvsdbg? And is it available on Linux?

@tripathics This is referring to the debugger configured in the launch.json file in VS Code. It'll be Windows specific as it's meant for using Visual Studio's toolset as the backend. It's briefly described in the launch json reference.

[tripathics]

@JJJohan Can I ask what is cppvsdbg? And is it available on Linux?

@tripathics This is referring to the debugger configured in the launch.json file in VS Code. It'll be Windows specific as it's meant for using Visual Studio's toolset as the backend. It's briefly described in the launch json reference.

Btw I am having problem with 2d or 3d array in watch.. idk how to use that pointer syntax for multidimensional arrays in watch.. can you help me?

[AmirhosseinR]

For 2d array use this (int pointer_2d[10][15];):
(int()[10][15])pointer_2d
and so on.

[batunpc]

For anyone who having issues still I found this working on my macOS if I put this on my watch window:
pointerName,[size]
(pay attention having no asterisk at the beginning)

[z6m8n7ljw]

For anyone who having issues still I found this working on my macOS if I put this on my watch window: pointerName,[size] (pay attention having no asterisk at the beginning)

The only way by far that works on my VS for mac !

[q1uyj]

All what you said doesn't work for me :(

[z6m8n7ljw]

All what you said doesn't work for me :(
In your case, this would be just like this: arr,[5]

[motla]

All what you said doesn't work for me :(

@Ch1ldr3n What debugger are you using? I presume LLDB cause I got the same issue.

[Ronalyo]

here's what i've gathered, hope this helps

general forms for expanding arrays (of any dimension, with arbitrary length):

1. **...arr@...@len2@len1: same amount of asterisks as dimensions, goes from top to bottom, where order of len is reversed
2. *(type(*)[len1][len2][...])arr: goes from bottom to top, order of len is as specified

there's also one for expanding 2 dimensions specifically:
*arr@len2,len1: len order reversed, seperate lens with comma

• bottom means element level, top means highest level, see examples for more clarity

---

Examples:

1. 1st(top) dimension has len = 4, 2nd has 2, 3rd has 3. unspecified dimensions use default len
   
2. highest shown(not top) dimension has len = 3, next has 2, next(bottom) has 4. unspecified dimensions isn't shown
   
   extra: special 2d expansion is basically method 1. with different syntax
   

[dsabala]

What is the reference of *some_pointer@3 syntax? Where is documentation of such a statements?

[spking11]

What is the reference of *some_pointer@3 syntax? Where is documentation of such a statements?

Here, and the comma syntax is here.

[jackiesogi]

All what you said doesn't work for me :(

I think it is because everyone use different types of debugger, it may look the same on the surface since vscode provides an unified UI, but the underlying debugger tool we are using is not the same. For example, I use LLDB as the debugger(you can search for the extension in vscode), the syntax some_pointer,[N] (no space) works well for me.

So, take a look at the documentation of the debugger(or debugger extension) you're using, and find something like Variable Formatting, you will learn about the syntax !