Suppose I've this nested loop
for (int a=1; a<MAX_A; ++a)
for (int b=1; b<MAX_B; ++b)
for (int c=1; c<MAX_C; ++c)
{
do_something(a, b ,c);
}
and I reuse this loop in various part of my code, changing the function do_something
. It's quite boring to rewrite every time the first three lines. In python for example I would created a generator to return an iterator (1, 1, 1), (1, 1, 2), ...
or something like itertools.product
.
In c++ the only solution I've in mind is to define a macro. Something better?e
Use templates:
template<typename Func>
inline void do_something_loop(Func f)
{
for (int a=1; a<MAX_A; ++a)
for (int b=1; b<MAX_B; ++b)
for (int c=1; c<MAX_C; ++c)
{
f(a, b ,c);
}
}
This can be called with any function pointer or function object that matches the signature, e.g.:
void do_something(int a, int b, int c) { /* stuff */ }
do_something_loop(do_something);
Or with a function object:
struct do_something
{
void operator()(int a, int b, int c) { /* stuff */ }
};
do_something_loop(do_something());
Or if your compiler supports C++11, even with a lambda:
do_something_loop([](int a, int b, int c) { /* stuff */ });
Note that you could also declare the f
parameter as a function pointer with the signature void(*f)(int,int,int)
instead of using a template, but that's less flexible (it won't work on function objects (including the result of std::bind) or lambdas).
Make a helper loop function:
template<typename Work>
void loop(Work work) {
for (int a=1; a<MAX_A; ++a)
for (int b=1; b<MAX_B; ++b)
for (int c=1; c<MAX_C; ++c)
{
work(a, b ,c);
}
}
Define the work to be done:
void some_work(int a, int b, int c) {
}
Then use:
loop(some_work);
Note that now you don't need to use only function, but you can use a function object (object for which an operator()
is overloaded).
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