[petsc-dev] need C++ expert help

[Eric Chamberland]

with m,n declared "int", for me 2 warnings arise from this line:

first, "write" takes a size_t argument:

write(fd,vals,(size_t)(m*n)*sizeof(double))

and returns a "ssize_t" value, so the rest of the line compiles fine 
like this:

!= (ssize_t)((size_t)(m*n)*sizeof(double)

which gives:

write(fd,vals,(size_t)(m*n)*sizeof(double)) != 
(ssize_t)((size_t)(m*n)*sizeof(double))

but that is somewhat ugly... :/

Eric



On 13/09/16 03:03 PM, 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
>