# Function pointer array crashing **URL:** \ **Category:** Help\ **Created:** [July 25, 2023, 8:08am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215 "2023-07-25T08:08:23Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 8:08am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/1 "2023-07-25T08:08:24Z")
Hello, I am testing function pointers in Fortran. I wonder if this piece of code is legit: ```auto program test_func_array implicit none type pp procedure(func_template), pointer, nopass :: f =>null() end type pp abstract interface function func_template(state) result(dstate) implicit none real, dimension(:,:), intent(in) :: state real, dimension(size(state(:,1)), size(state(1,:))) :: dstate end function end interface type(pp) :: func_array(4) real, dimension(4,6) :: state func_array(1)%f => zero_state print*,func_array(1)%f(state) contains function zero_state(state) result(dstate) implicit none real, dimension(:,:), intent(in) :: state real, dimension(size(state(:,1)), size(state(1,:))) :: dstate dstate = 0. end function zero_state end program test_func_array ``` If I try to compile it with `gfortran`, I get a crash: ```auto 951: internal compiler error: spec_dimen_size(): Bad dimension 0x7f3db2946082 __libc_start_main ../csu/libc-start.c:308 Please submit a full bug report, with preprocessed source if appropriate. Please include the complete backtrace with any bug report. See for instructions. ``` If I use `flang`, it compiles then at run time, I get this: ```auto test_f_array: malloc.c:2379: sysmalloc: Assertion `(old_top == initial_top (av) && old_size == 0) || ((unsigned long) (old_size) >= MINSIZE && pr ev_inuse (old_top) && ((unsigned long) old_end & (pagesize - 1)) == 0)' failed. [1] 118664 abort (core dumped) ./test_f_array ``` The problem seems to relate to the dimensionality of the state variables. If I have just scalars. The code compiles fine on `gfortran`. And in `flang`, even explicit dimensions compile and run fine. Any help on the topic is greatly appreciated (possibly, if someone has an easy access to different compilers, that would be interesting). Thanks! /Eelis ---
**Author:** ![FedericoPerini](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/federicoperini/32/1750_2.png) [@FedericoPerini](https://fortran-lang.discourse.group/u/FedericoPerini)\ **Post date:** [July 25, 2023, 8:15am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/2 "2023-07-25T08:15:37Z")
Welcome to the Discourse @eelis! Proper syntax for your function interface would be ```fortran real, dimension(size(state,1), size(state,2)) :: dstate ``` See the [fortran-lang documentation for size](https://fortran-lang.org/learn/intrinsics/array/#size). ---
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 8:38am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/3 "2023-07-25T08:38:50Z")
Thank you very much @FedericoPerini ! The fix you provide works perfectly on `flang`. However, on `gfortran` it still crashes with the same error message. Even with explicit definition of dimensions it does the same. I wonder if it is a compiler bug? I should test with a newer version. I have `9.4.0`. ---
**Author:** ![FedericoPerini](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/federicoperini/32/1750_2.png) [@FedericoPerini](https://fortran-lang.discourse.group/u/FedericoPerini)\ **Post date:** [July 25, 2023, 9:06am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/4 "2023-07-25T09:06:08Z")
You may have hit a compiler bug. Compiler tests can be done with the [compiler explorer](https://godbolt.org/z/WfzeoE8vx) ---
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 9:27am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/5 "2023-07-25T09:27:48Z")
Oh wow, thanks! I didn’t know about that site, very nice! I will have to report the bug then. Br, Eelis ---
**Author:** ![Pap](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pap/32/1305_2.png) [@Pap](https://fortran-lang.discourse.group/u/Pap)\ **Post date:** [July 25, 2023, 9:32am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/6 "2023-07-25T09:32:14Z")
Hi @eelis, and welcome to the Fortraners’ discourse. There are many people here wanting to help and/or discuss things, I’m sure you will find this very helpful and productive. I was typing my answer, but @FedericoPerini was faster. 😆 Your problem is a very common pitfall people have with the `size` intrinsic. Admittedly, gfortran’s [documentation](https://gcc.gnu.org/onlinedocs/gcc-13.1.0/gfortran/SIZE.html) about `size` doesn’t clarify that, but if you don’t pass the optional (second) argument `dim` to it, `size` will return a _vector_, even if the array is one-dimensional. The frustration probably comes from the fact the `dim` argument was added in Fortran 2003; in Fortran 90 you just had to live with the less flexible version of `size`, where the result is always a vector. Anyway, using `dim` with `size(state,1)` instead of `size(state(:,1))` _should_ fix the problem - except it doesn’t in gfortran (tested with version 12.2.0 and the latest stable release, 13.1.0) This is probably a bug, but I doubt it has to do with `size` iteself. It rather comes from the fact you define and use an _array_ of `type(pp)` elements. If you replace `func_array` with a `type(pp)` _scalar_, it actually works. **Edit** : It’s not relevant, but might worth mentioning: there is no need to add `implicit none` in `zero_state`’s body. The function is contained in the main program, therefore it inherits the `implicit none` from there. ---
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 10:43am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/7 "2023-07-25T10:43:29Z")
Thank you for the very informative answer @Pap! I am very happy about this forum. Also very happy to see the recent development in Fortran infrastructure and community. I am happy to learn the three pieces of information that you provided in your answer. All new to me. Cheers, Eelis ---
**Author:** ![Pap](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pap/32/1305_2.png) [@Pap](https://fortran-lang.discourse.group/u/Pap)\ **Post date:** [July 25, 2023, 11:10am UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/8 "2023-07-25T11:10:24Z")
Also tested with both ifort and ifx compilers. It works, as it should be. This is clearly a gfortran bug worth reporting. For some reason gfortan doesn’t like arrays of a derived type like this one, but doesn’t have any problem when it is a scalar. Weird… ---
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [July 25, 2023, 2:07pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/9 "2023-07-25T14:07:36Z")
> [@FedericoPerini](#): > > `size(x)` will return an 1-dim array if you don’t specify a dimension, e.g., > [@Pap](#): > > if you don’t pass the optional (second) argument `dim` to it, `size` will return a _vector_, These are not correct. `size` always returns a scalar. > 16.9.194 SIZE (ARRAY [, DIM, KIND]) > > **Description.** Size of an array or one extent. > > **Class.** Inquiry function. > > **Arguments.** > > ARRAY shall be assumed-rank or an array. It shall not be an unallocated allocatable variable or a pointer that is not associated. If ARRAY is an assumed-size array, DIM shall be present with a value less than the rank of ARRAY. > > DIM (optional) shall be an integer scalar with a value in the range 1 ≤ DIM ≤ n, where n is the rank of ARRAY. > > KIND (optional) shall be a scalar integer constant expression. > > **Result Characteristics.** Integer scalar. If KIND is present, the kind type parameter is that specified by the value of KIND; otherwise the kind type parameter is that of default integer type. > > **Result Value.** If DIM is present, the result has a value equal to the extent of dimension DIM of ARRAY, except that if ARRAY is assumed-rank and associated with an assumed-size array and DIM is present with a value equal to the rank of ARRAY, the value is −1. > > If DIM is absent and ARRAY is assumed-rank, the result has a value equal to PRODUCT(SHAPE(ARRAY, KIND)). Otherwise, the result has a value equal to the total number of elements of ARRAY. That said, `size(state,dim=1)` is more appropriate clearer than `size(state(:,1))`, and works even if `size(state,dim=2) == 0` where you would get a segfault in the latter case. ---
**Author:** ![Pap](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pap/32/1305_2.png) [@Pap](https://fortran-lang.discourse.group/u/Pap)\ **Post date:** [July 25, 2023, 3:43pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/10 "2023-07-25T15:43:41Z")
I am 1000% sure, not jut 100%, that `size(x)` used to return a vector, even if it was a vector of one element only. If they broke that rule later on, when `dim` was introduced, I don’t know, really. That’s because I always used `dim` since Fortran 2003, exactly because I was fed up with those one-element vectors I used to get all the time before `dim`. So unless I’m terribly wrong here (and I am not,) that breaks backwards compatibility - admittedly, very slightly, but it does. Fortran is notorious for backwards compatibility. ---
**Author:** ![RonShepard](https://avatars.discourse-cdn.com/v4/letter/r/a3d4f5/32.png) [@RonShepard](https://fortran-lang.discourse.group/u/RonShepard)\ **Post date:** [July 25, 2023, 3:56pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/12 "2023-07-25T15:56:50Z")
> [@kargl](#): > > ```auto > Examples. The value of SIZE (A (2:5, ­1:1), DIM=2) is 3. The value of > SIZE (A (2:5, ­1:1) ) is 12. > > ``` In my browser, I think there are some missing minus signs in this text. This ```auto Examples. The value of SIZE (A (2:5,-1:1), DIM=2) is 3. The value of SIZE (A (2:5,-1:1) ) is 12. ``` looks right. ---
**Author:** ![Pap](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pap/32/1305_2.png) [@Pap](https://fortran-lang.discourse.group/u/Pap)\ **Post date:** [July 25, 2023, 3:59pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/13 "2023-07-25T15:59:53Z")
I don’t really care what the standard says, and frankly, I won’t even check it out. That’s because I know what the Fortran 90 compilers I used did. And they did as I said, period. It was so common that I had my own function `ssize` to return a scalar when the array only had one dimension. That’s because `size(x)(1)` won’t work, so I needed to temporarily store the result of `size` and extract its one and only element. ---
**Author:** ![FedericoPerini](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/federicoperini/32/1750_2.png) [@FedericoPerini](https://fortran-lang.discourse.group/u/FedericoPerini)\ **Post date:** [July 25, 2023, 4:38pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/14 "2023-07-25T16:38:22Z")
I do apologize @eelis for the mistake. I believe @Pap and I got confused as this polymorphic behavior is indeed present in other array size functions (such as, for example, `lbound`, `ubound` ), and an error was being discussed, so my mind went immediately to that. Like @Pap suggests, I also like to never use `size(x)` without a dimension on a 1D array because I’m dumb and I know that it’s “safer” to always specify it. ---
**Author:** ![Pap](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pap/32/1305_2.png) [@Pap](https://fortran-lang.discourse.group/u/Pap)\ **Post date:** [July 25, 2023, 4:49pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/15 "2023-07-25T16:49:59Z")
@FedericoPerini If you used Fortran compilers back when `dim` didn’t exist, they always returned a vector (yes, I insist that’s a _fact_, not an opinion.) So you aren’t dumb. It is quite plausible to assume they will always do the same, given Fortran’s backwards compatibility. I actually found old projects of mine, where a custom `ssize` function is used instead of `size`, just to dodge the fact `size(x)` returned a vector no matter what. ---
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 5:33pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/18 "2023-07-25T17:33:56Z")
Thanks man! I will try to report it. Unfortunately, I don’t remember my password to their bugzilla. I tried to recover it but the recovery email does not come through… ---
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 5:35pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/19 "2023-07-25T17:35:28Z")
Thank you for the clarification. btw. I like your Youtube channel. Waiting for more content 😉 ---
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 5:40pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/20 "2023-07-25T17:40:48Z")
@FedericoPerini All good! I appreciate the help and quick response. The code got better with your fixes. Thanks! ---
**Author:** ![eelis](https://avatars.discourse-cdn.com/v4/letter/e/c6cbf5/32.png) [@eelis](https://fortran-lang.discourse.group/u/eelis)\ **Post date:** [July 25, 2023, 5:42pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/21 "2023-07-25T17:42:43Z")
And obviously you are not dumb! ---
**Author:** ![everythingfunctional](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/everythingfunctional/32/176_2.png) [@everythingfunctional](https://fortran-lang.discourse.group/u/everythingfunctional)\ **Post date:** [July 25, 2023, 6:21pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/22 "2023-07-25T18:21:22Z")
> [@eelis](#): > > Waiting for more content 😉 My content is ending up on the NERSC YouTube channel lately: > **[NERSC](https://www.youtube.com/@theRealNERSC)** > > The National Energy Research Scientific Computing Center (NERSC) provides high-performance scientific computing to power the basic research missions of the U.S. Department of Energy's Office of Science (DOE-SC). As a DOE-SC national user facility, we... ---
**Author:** ![Pap](https://yyz2.discourse-cdn.com/free1/user_avatar/fortran-lang.discourse.group/pap/32/1305_2.png) [@Pap](https://fortran-lang.discourse.group/u/Pap)\ **Post date:** [July 25, 2023, 6:51pm UTC](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215/23 "2023-07-25T18:51:55Z")
> [@kargl](#): > > Well, whatever compilers you were using were not Fortran compilers. Period. Or so you think… and you are so wrong. 😆 I don’t care what the standard said, I know the reality, what compilers did. My best guess is that you probably wasn’t programming back then to know that reality. And if you did, you obviously didn’t do it in Fortran. So maybe you should be more careful with your statements. Or not, I don’t really care. What I do know is that **you are not going to “teach” me what I know for a fact**. **P-E-R-I-O-D**. I hope that’s clear enough. That being said, I’m not going to comment again on your posts, which I honestly don’t know why they tend to be offensive. And now for the important part: I apologize to @eelis for the false statement concerning `size`. It was based on the reality of Fortran compilers back when `size` didn’t have optional arguments, and the very plausible assumption they still do the same, given the notorious Fortran backwards compatibility. [Next page](https://fortran-lang.discourse.group/t/function-pointer-array-crashing/6215.md?page=2)