compiling.texi

c++经典教材 Blitz++ v0.8

@node compiling
@section Compiling with Blitz++

@subsection Header files
@cindex header files, convention
@cindex @file{blitz} header files

Blitz++ follows an X-windows style convention for header files.  All headers
are referred to with a prefix of @file{blitz}.  For example, to use the
@code{Array<T,N>} class, one needs to include @code{<blitz/array.h>} instead
of just @code{<array.h>}.  To make this work, the main Blitz++ directory
must be in your include path.  For example, if Blitz++ was installed in
@file{/software/Blitz++}, you will need to compile with @code{-I
/software/Blitz++}.

If you have root privileges, you may want to put in a symbolic link from the
standard include path (e.g. @file{/usr/include/blitz/}) to the @code{blitz}
directory of the distribution.  This will allow you to omit the @code{-I
...} option when compiling.

@subsection Linking to the Blitz++ library
@findex libblitz.a
@cindex library (@file{libblitz.a})

The Blitz++ library file @file{libblitz.a} contains a few pieces of global
data.  You should ensure that the @file{lib} subdirectory of the Blitz++
distribution is in your library path (e.g.
@code{-L/usr/local/blitz-0.5/lib}) and include @code{-lblitz} on your
command line.  If you use math functions, you should also compile with
@code{-lm}.

@subsection An example Makefile
@cindex makefile, example

Here is a typical skeletal Makefile for compiling with Blitz++ under gcc:

@smallexample
@include examples/makefile.example
@end smallexample

There are more example makefiles in the examples, testsuite, and benchmarks
directories of the distribution.

@subsection Explicit instantiation
@cindex explicit instantiation
@cindex Array explicit instantiation

It is not possible to do explicit instantiation of Blitz++ arrays.  If you
aren't familiar with explicit instantiation of templates, then this fact
will never bother you.

The reason is that explicit instantiation results in all members of a class
template being instantiated.  This is @strong{not} the case for implicit
instantiation, in which only required members are instantiated.  The
@code{Array<T,N>} class contains members which are not valid for all types
@code{T}: for example, the binary AND operation @code{&=} is nonsensical if
@code{T=float}.  If you attempt to explicitly instantiate an array class,
e.g.

@code{template class Array<float,3>;}

then you will be rewarded with many compile errors, due to methods such as
@code{&=} which are nonsensical for @code{float}.

As some consolation, explicit instantiation would not be much help with
Blitz++ arrays.  The typical use for explicit instantiation is to
instantiate all the templates you need in one compilation unit, and turn off
implicit instantiation in the others -- to avoid duplicate instantiations
and reduce compile times.  This is only possible if you can predict ahead of
time what needs instantiation.  Easy for simple templates, but impossible
for classes like @code{Array}.  Almost every line of code you write using
@code{Array} will cause a different set of things to be implicitly
instantiated.