Information Technology Reference
In-Depth Information
std::valarray<double> u(n+1);
The
u
array is automatically deleted when it is no longer in use. The declaration of
arrays of type
valarray
in a function such as
heun
is as follows:
void heun (fptr f, double u0, double dt, int n,
std::valarray<double>& u)
The ampersand
&
indicates that a
reference
to the
u
object is transferred; without
the ampersand,
u
will be a copy of the transferred array. This is not what we want,
since our goal is to compute values in
u
and view these values outside the
heun
function. The syntax of the body of the
heun
function is independent of whether we
use
std::valarray
or plain C/C
CC
arrays.
Multi-dimensional arrays in C and C
CC
can be constructed, but the allocation
and use of
new
is more complicated. Details can be found in topics on the C or C
CC
programming language. Unfortunately, the standard C
CC
library does not offer a
class such as
valarray
for multi-dimensional arrays. One can, nevertheless, create
a class for multi-dimensional arrays with minor effort. There are also several open
source and commercial libraries in C
CC
that offer sophisticated multi-dimensional
arrays for numerical computing.
File Writing
Basic file writing in C
CC
is illustrated next
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:
std::ofstream out("sol.dat"); // open a file sol.dat
out << "some text " << object << " more text\n";
out.close()
A
dump
function for writing the
u
.t /
values to a file can typically be coded as
follows:
void dump (std::ostream& out, double u[], int n, double t0, double dt)
{
double time = t0;
for (int i = 0; i <= n; i++) {
out << time << " " << u[i] << '\n';
time += dt;
}
}
Although the file is of type
std::ofstream
, it is common to declare the corre-
sponding function argument as
std::ostream
, because this type is a common name
for all types of output media. For example, the
out
argument above can be a file
(
std::ofstream
) or the terminal window (
std::cout
), or even a string.
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This is C
file writing. One can also use the C functionality for file writing. This can be
convenient if format control via the
fprintf
function is desired.
CC
