# Question on Variable length datatypes -memory related **URL:** \ **Category:** Hdf-forum archives\ **Created:** [May 11, 2009, 9:34am UTC](https://forum.hdfgroup.org/t/question-on-variable-length-datatypes-memory-related/1272 "2009-05-11T09:34:33Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![ramakrishnan.iyer](https://forum.hdfgroup.org/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@ramakrishnan.iyer](https://forum.hdfgroup.org/u/ramakrishnan.iyer)\ **Post date:** [May 11, 2009, 9:34am UTC](https://forum.hdfgroup.org/t/question-on-variable-length-datatypes-memory-related/1272/1 "2009-05-11T09:34:33Z")
All, Consider this - Allocation of memory for a variable length data type ( which is intended to store dataset region references ) . I am assigning the length ( non-zero and +ve) and allocating the memory using malloc . offsets is of type hvl\_t and Data is the structure holding offsets . Data.offsets.len=numPart; Data.offsets.p = (hdset\_reg\_ref\_t\*)malloc(numPart\*sizeof(hdset\_reg\_ref\_t)); Deallocation of memory: I am freeing the memory as given below if(Data.offsets.len\>0) free(Data.offsets.p); I do not make a call to H5Dvlen\_reclaim . Is there any chance of memory leak in this case ? Regards Ram ---
**Author:** ![Quincey\_Koziol](https://forum.hdfgroup.org/letter_avatar_proxy/v4/letter/q/dbc845/32.png) [@Quincey\_Koziol](https://forum.hdfgroup.org/u/Quincey_Koziol)\ **Post date:** [May 12, 2009, 1:50am UTC](https://forum.hdfgroup.org/t/question-on-variable-length-datatypes-memory-related/1272/2 "2009-05-12T01:50:42Z")
Hi Ram, > **···** > > On May 11, 2009, at 4:34 AM, Ramakrishnan Iyer wrote: > > > All, > > > > Consider this – > > > > Allocation of memory for a variable length data type ( which is intended to store dataset region references ) . I am assigning the length ( non-zero and +ve) and allocating the memory using malloc . > > > > offsets is of type hvl\_t and Data is the structure holding offsets . > > > > Data.offsets.len=numPart; > > > > Data.offsets.p = (hdset\_reg\_ref\_t\*)malloc(numPart\*sizeof(hdset\_reg\_ref\_t)); > > > > Deallocation of memory: I am freeing the memory as given below > > > > if(Data.offsets.len\>0) free(Data.offsets.p); > > > > I do not make a call to H5Dvlen\_reclaim . > > Is there any chance of memory leak in this case ? > >   Seems OK to me... > >     Quincey ---
**Author:** ![Vesa\_Paatero](https://forum.hdfgroup.org/letter_avatar_proxy/v4/letter/v/76d3ee/32.png) [@Vesa\_Paatero](https://forum.hdfgroup.org/u/Vesa_Paatero)\ **Post date:** [May 12, 2009, 8:38am UTC](https://forum.hdfgroup.org/t/question-on-variable-length-datatypes-memory-related/1272/3 "2009-05-12T08:38:29Z")
Dear Ramakrishnan and other C programmers, The example you provided may be affected by the special case of numPart being 0. I think I read somewhere that malloc(0) is a valid operation which returns a unique pointer that should be freed as any malloc allocation. However, I'm not exactly sure if that is part of the prevalent version standard C or something less universal. I don't know if numPart==0 is a relevant possibility in your application, but my typical approach for avoiding memory allocation bugs is to initialize pointers (Data.offsets.p) to zero and free them with something like if(Data.offsets.p) free(Data.offsets.p); Best Regards,     Vesa Paatero > **···** > > From: Ramakrishnan Iyer [[mailto:ramakrishnan.iyer@altair.com](mailto:ramakrishnan.iyer@altair.com)] > Sent: 11. toukokuuta 2009 12:35 > To: HDF forum > Subject: [hdf-forum] Question on Variable length datatypes -memory related > Importance: High > > All, > Consider this - > Allocation of memory for a variable length data type ( which is intended to store dataset region references ) . I am assigning the length ( non-zero and +ve) and allocating the memory using malloc . > offsets is of type hvl\_t and Data is the structure holding offsets . > Data.offsets.len=numPart; > Data.offsets.p = (hdset\_reg\_ref\_t\*)malloc(numPart\*sizeof(hdset\_reg\_ref\_t)); > > Deallocation of memory: I am freeing the memory as given below > if(Data.offsets.len\>0) free(Data.offsets.p); > I do not make a call to H5Dvlen\_reclaim . > Is there any chance of memory leak in this case ? > > Regards > Ram ---
**Author:** ![ramakrishnan.iyer](https://forum.hdfgroup.org/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@ramakrishnan.iyer](https://forum.hdfgroup.org/u/ramakrishnan.iyer)\ **Post date:** [May 12, 2009, 8:45am UTC](https://forum.hdfgroup.org/t/question-on-variable-length-datatypes-memory-related/1272/4 "2009-05-12T08:45:01Z")
Dear Vesa, On numPart being 0, the Data.offsets.len is made 0 and the memory is not allocated ( It's just that , this is not shown in the code below ) . Regards Ram > **···** > > -----Original Message----- > From: Vesa Paatero [[mailto:Vesa.Paatero@biolinscientific.com](mailto:Vesa.Paatero@biolinscientific.com)] > Sent: Tuesday, May 12, 2009 2:08 PM > To: Ramakrishnan Iyer; HDF forum > Subject: RE: Question on Variable length datatypes -memory related > > Dear Ramakrishnan and other C programmers, > > The example you provided may be affected by the special case of numPart > being 0. I think I read somewhere that malloc(0) is a valid operation > which returns a unique pointer that should be freed as any malloc > allocation. However, I'm not exactly sure if that is part of the > prevalent version standard C or something less universal. > > I don't know if numPart==0 is a relevant possibility in your > application, but my typical approach for avoiding memory allocation bugs > is to initialize pointers (Data.offsets.p) to zero and free them with > something like if(Data.offsets.p) free(Data.offsets.p); > > Best Regards, > >     Vesa Paatero > > From: Ramakrishnan Iyer [[mailto:ramakrishnan.iyer@altair.com](mailto:ramakrishnan.iyer@altair.com)] > Sent: 11. toukokuuta 2009 12:35 > To: HDF forum > Subject: [hdf-forum] Question on Variable length datatypes -memory > related > Importance: High > > All, > > Consider this - > > Allocation of memory for a variable length data type ( which is intended > to store dataset region references ) . I am assigning the length ( > non-zero and +ve) and allocating the memory using malloc . > > offsets is of type hvl\_t and Data is the structure holding offsets . > > Data.offsets.len=numPart; > > Data.offsets.p = > (hdset\_reg\_ref\_t\*)malloc(numPart\*sizeof(hdset\_reg\_ref\_t)); > > Deallocation of memory: I am freeing the memory as given below > > if(Data.offsets.len\>0) free(Data.offsets.p); > > I do not make a call to H5Dvlen\_reclaim . > > Is there any chance of memory leak in this case ? > > Regards > > Ram