Initializing a large const array?
Anyway, to initialize a large const array without putting all the elements inside it, like this:
trying to create an array:
const double A[1000] = {1.0/1, 1.0/2, 1.0/3,...,1.0/1000};
It's easy to do with a loop.
If it really should be const, and you have 1000 different values, write some kiddy / script application to spit it out as a header file and prevent text from being entered! This gives you an easy way to change the initialization of the entire array later if needed.
To do this, you can use the boost preprocessor library:
Your main file:
#include <boost/preprocessor.hpp>
const double A[1000] = {
#define BOOST_PP_ITERATION_LIMITS (0, 9)
#define BOOST_PP_FILENAME_1 "toplevel.hpp"
#include BOOST_PP_ITERATE()
};
File "toplevel.hpp"
:
#define ENUMERATE(z, i, data) 1.0 / (BOOST_PP_ITERATION() * 100 + i)
BOOST_PP_COMMA_IF(BOOST_PP_ITERATION()) BOOST_PP_ENUM(100, ENUMERATE, %%)
#undef ENUMERATE
It works by including "toplevel.hpp" ten times in a row, while BOOST_PP_ITERATION()
expanding to 0, 1, .. 9 on each iteration (0 and 9 comes from BOOST_PP_ITERATION_LIMITS
).
BOOST_PP_COMMA_IF()
creates a comma if the argument is nonzero.
BOOST_PP_ENUM()
expands the macro ( ENUMERATE
in this case) 100 times and i
gets values from 0 to 99 (based on the argument 100
).
EDIT
Added explanation and removed unnecessary BOOST_PP_OR()
.
EDIT 2
This two-step iteration (file and macro inside it) should be used as most of the iteration schemes in boost :: preprocessor are limited to max. 256 iterations (as stored in various macros BOOST_PP_LIMIT_*
).
It can also be done using nested BOOST_PP_ENUM () without iterating over the file.
If I had to do this, I would probably write a small program to do this:
for(i = 1; i <= 1000; i++)
{
printf("1/%d.0, ", i);
if(i % 10 == 0) printf("\n");
}
I thought you could do it with macros and I'm sure it can be done, but I can't get it to work right now. I will return if I earn.
You can create an array of pointers to const char so that you can initialize them at runtime with new with a loop.
Otherwise, I don't believe there is a way. You can either just go ahead, initialize it manually in the header file, or strip it out of status const
. If it doesn't initialize at compile time, the compiler complains that it doesn't initialize the variable const
.