[petsc-dev] need C++ expert help

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:

>    The problem is ssize_t is not portable to Microsoft.

Is that still true?

Note that the example is buggy in the first place -- write can return
successfully after writing less than all the bytes so you typically need
to call it in a loop.

Why not make this example use fwrite -- it's portable and does what you want.

>> On Sep 13, 2016, at 3:05 PM, Munson, Todd <tmunson at mcs.anl.gov> wrote:
>> 
>> 
>> The write statement return type is ssize_t.  For whatever reason its a signed type
>> because it can return -1 on error.
>> 
>> I would suggest using the ssize_t type for both and changing the "!=" to a "<"
>> which will abort if write either returns a negative or the number of bytes 
>> written is not correct.
>> 
>> Note: you will have problems if (ssize_t) (m*n*sizeof(double)) is negative 
>> though, but that can be checked as well.
>> 
>> Todd.
>> 
>>> On Sep 13, 2016, at 2:50 PM, Satish Balay <balay at mcs.anl.gov> wrote:
>>> 
>>> This works..
>>> 
>>> Satish
>>> 
>>> ---------
>>> 
>>> diff --git a/src/mat/examples/tests/ex45.c b/src/mat/examples/tests/ex45.c
>>> index 63d0a30..37f68e3 100644
>>> --- a/src/mat/examples/tests/ex45.c
>>> +++ b/src/mat/examples/tests/ex45.c
>>> @@ -72,7 +72,7 @@ void Store2DArray(int m,int n,double *a,const char *filename,int *fdd)
>>>      vals[i+m*j] = a[j+i*n];
>>>    }
>>>  }
>>> -  if (write(fd,vals,m*n*sizeof(double)) != ((unsigned int) (m*n))*sizeof(double)) abort();
>>> +  if ((size_t)write(fd,vals,m*n*sizeof(double)) != (size_t)(m*n*sizeof(double))) abort();
>>>  free(vals);
>>> 
>>> }
>>> @@ -94,7 +94,7 @@ void Store1DArray(int m,double *a,const char *filename,int *fdd)
>>>  }
>>>  if (write(fd,&classid,sizeof(int)) != sizeof(int)) abort();
>>>  if (write(fd,&m,sizeof(int)) != sizeof(int)) abort();
>>> -  if (write(fd,a,m*sizeof(double)) != ((unsigned int)m)*sizeof(double)) abort();
>>> +  if ((size_t)write(fd,a,m*sizeof(double)) != (size_t)(m*sizeof(double))) abort();
>>> }
>>> 
>>> 
>>> On Tue, 13 Sep 2016, Satish Balay wrote:
>>> 
>>>> I would tink if its typecast to same type - comparision would work..
>>>> 
>>>> if ((ssize_t)write(fd,vals,m*n*sizeof(double)) != (ssize_t)(m*n*sizeof(double))) abort();
>>>> 
>>>> I'll give this a try...
>>>> 
>>>> Satish
>>>> 
>>>> On Tue, 13 Sep 2016, Barry Smith wrote:
>>>> 
>>>>> 
>>>>>  I need help from someone who knows the subtleties of c++.  We have a PETSc example that always compiles fine with C but generates annoying warnings with C++. I've tried many different variants to eliminate the warnings with no luck
>>>>> 
>>>>>  Any help is appreciated.
>>>>> 
>>>>>   Barry
>>>>> 
>>>>> 
>>>>> mpicxx -o ex45.o -c -Wall -Wwrite-strings -Wno-strict-aliasing -Wno-unknown-pragmas -fvisibility=hidden -g -O   -fPIC    -I/sandbox/petsc/petsc.clone-3/include -I/sandbox/petsc/petsc.clone-3/arch-linux-opt-cxx-quad/include -I/usr/include/mpich2    `pwd`/ex45.c
>>>>> /sandbox/petsc/petsc.clone-3/src/mat/examples/tests/ex45.c: In function ‘void Store2DArray(int, int, double*, const char*, int*)’:
>>>>> /sandbox/petsc/petsc.clone-3/src/mat/examples/tests/ex45.c:75:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
>>>>>  if (write(fd,vals,m*n*sizeof(double)) != ((unsigned int) (m*n))*sizeof(double)) abort();
>>>>>                                        ^
>>>>> /sandbox/petsc/petsc.clone-3/src/mat/examples/tests/ex45.c: In function ‘void Store1DArray(int, double*, const char*, int*)’:
>>>>> /sandbox/petsc/petsc.clone-3/src/mat/examples/tests/ex45.c:97:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
>>>>>  if (write(fd,a,m*sizeof(double)) != ((unsigned int)m)*sizeof(double)) abort();
>>>>> 
>>>>> 
>>>>> It can be found here ftp://ftp.mcs.anl.gov/pub/petsc/nightlylogs/archive/2016/09/13/examples_next_arch-linux-opt-cxx-quad_grind.log
>>>> 
>> 
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