PGI User Forum

[depietri]

Dear all:

I am having trouble with the protopoy of "pow" in C++.
I am asking suggestion to avoid to manualy change a system
include file. With the change reported below I was able to succesfully compile my code. However since this is a multiplatform code
I would like to advoid such local changes.

Any suggestions?

Details below:

In particular I had to manualy add this prototype in: math.h

[Deborah Caruso]

Depietri -

C++ is a tightly typed language. It looks like you
are passing an integer value as the second parameter,
when pow expects a double. The change to math.h is not
the portable solution. Since you did not include
a small test case, I can only make the suggestion
that you change the line

for (int d=0; d<D; ++d) r[d]=pow(a[d],b[d]);

to

for (int d=0; d<D; ++d) r[d]=pow(a[d],(double) b[d]);

and see if that works. The second parameter must be of type
double.

[depietri]

Dear Caruso:

I known of this tricks. I was wondering the reason why I was not getting
the correct call to pow(double,int). The code I am having the problem
is part of a gig 100000+ line of codes multiplatform application and
we whould like to advoid different version for different compiler.

Looking in Strouststrup "The C++ Programming language, Special edition"
at pag. 660 section 22.3 it is mentioned that the header of <cmath>
and <math.h> should include a prototype to "double pow(double,int)"
and there are very good reason do be that way.

It is well known that pow(double,double) is a very difficult function to
be implemented and should be advoid, when possible.

In fact in the sample code (an extract) I submited there is the
include line

[Deborah Caruso]

If you can be sure that your libc.a contains a function declared as pow(doube, int)
then your original fix is fine. We do not provide libc.a , and only provide
a math.h to deal with some portablility and C++ issues. Our math.h uses an
include_next directive to include the original system file. -Deb Caruso