[Mpi-forum] Compile problems with examples in MPI Standard

[John DelSignore]

OK, I see. You have argv_p as type "a pointer to an array of pointer to char". That must prevent the compiler from converting the "array" to a "pointer". I think if you drop the parens around the "(*argv_p)", you'll get the same stylistic effect, but it won't prevent the compiler from converting the "[]" to "*", and that seems to silence the warning:

cap:/nfs/san0/user/home/jdelsign>cat xxx.c
void bill(      char *((*p)[])) {}
void john(      char *( *p [])) {}
main(int argc, char *argv[])
{
  bill(&argv);
  john(&argv);
}
cap:/nfs/san0/user/home/jdelsign>gcc xxx.c
xxx.c: In function 'main':
xxx.c:5: warning: passing argument 1 of 'bill' from incompatible pointer type
cap:/nfs/san0/user/home/jdelsign>

Cheers, John D.


William Gropp wrote:
> Here's the test case for everyone.  No const.
> 
> int MPI_Init( int *argc_p, char *((*argv_p)[]) );
> int main( int argc, char *argv[] )
> { 
>      MPI_Init( &argc, &argv );
>      return 0;
> }  
> 
> This gives a warning with my gcc:
> 
> GroppsMac3:MPI-3.0 gropp$ gcc -c f1.c
> f1.c: In function ‘main’:
> f1.c:4: warning: passing argument 2 of ‘MPI_Init’ from incompatible pointer type
> 
> William Gropp
> Director, Parallel Computing Institute
> Deputy Director for Research
> Institute for Advanced Computing Applications and Technologies
> Paul and Cynthia Saylor Professor of Computer Science
> University of Illinois Urbana-Champaign
> 
> 
> 
> On Jul 24, 2012, at 10:17 AM, John DelSignore wrote:
> 
>> In C and C++, the type of "char *argv[]" as a parameter is equivalent to the type of "char **argv", because you can't pass an array as an argument. Therefore, as written in the example, the type of argv is "a pointer to a pointer to a char".
>>
>> I don't know what the type signature of MPI_Init() is in your implementation, but it's possible that a "const" got tossed in there somewhere, for example: int MPI_Init(int *, const char ***);
>>
>> Here's a simple test:
>>
>> cap:/nfs/san0/user/home/jdelsign>cat xxx.c
>> void bar(      char ***p) {}
>> void foo(const char ***p) {}
>> main(int argc, char *argv[])
>> {
>>  bar(&argv);
>>  foo(&argv);
>> }
>> cap:/nfs/san0/user/home/jdelsign>gcc --version | head -1
>> gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-44)
>> cap:/nfs/san0/user/home/jdelsign>gcc xxx.c
>> xxx.c: In function 'main':
>> xxx.c:6: warning: passing argument 1 of 'foo' from incompatible pointer type
>> cap:/nfs/san0/user/home/jdelsign>
>>
>> Hope this helps.
>>
>> Cheers, John D.
>>
>>
>>
>> William Gropp wrote:
>>> I've run my code checker over the examples in the MPI-3 Standard, and I've found some issues.  Perhaps the biggest is this (a typical example):
>>>
>>> Opening file one-side-2.tex
>>> ex5501.c: In function ‘main’:
>>> ex5501.c:58: warning: passing argument 2 of ‘MPI_Init’ from incompatible pointer type
>>>
>>> This occurs everywhere we include MPI_Init in an example.  The compiler is gcc 4.2.1 .  The corresponding 
>>> declaration of argv is as intended:
>>>
>>> int main(int argc, char *argv[]) 
>>>
>>> The declaration in MPI_Init looks correct (argv is a pointer to an array of pointers to char).  Is this a place where we should stick with the *** notation just to keep compilers happy?  Or is there something I'm missing in the declaration?
>>>
>>> There are a number of other errors as well.  Three examples in the new tools chapter don't compile.  There are a number of problems in the datatype chapter, most minor.
>>>
>>> I can fix the obvious ones or leave them to the chapter authors.  Let me know what is preferred.
>>>
>>> I can't check the Fortran 08 examples because I only have gfortran :( 
>>>
>>> Bill
>>>
>>> William Gropp
>>> Director, Parallel Computing Institute
>>> Deputy Director for Research
>>> Institute for Advanced Computing Applications and Technologies
>>> Paul and Cynthia Saylor Professor of Computer Science
>>> University of Illinois Urbana-Champaign
>>>
>>>
>>>
>>>
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