Multi dimentionnal for loop - c

Question

Is there a simple way to convert this
for (int i=0; i < 31; i++)
for (int j=0; j < 74; j++)
for (int k=1; k < 12; k++)
for (int l=13; l < 15; l++)
...
To a simpler this
mfor (int start[]={0,0,1,13}; int max[]={31,74,12,15}) {
printf("%i %i\n", start[1], start[3]);
}
Is there a macro or a plugin-like ?
This loop can iterate thought Tensor (like an image) to do stuff like Tensor Convolution or Pooling. In any dimentions (can be more than 4)
Or how to add some syntax to C. I have the implementation for mfor loop. Because for loop is in real a while loop.

Answer 1

There's no simple way, but you could implement an iterator-like type that generates the Cartesian product over n given ranges:
enum {
MAX = 8
};
typedef struct Combinator Combinator;
struct Combinator {
size_t index; // running index of generated numbers
size_t n; // number of dimensions
int data[MAX]; // current combination
int start[MAX]; // lower and ...
int end[MAX]; // .. exclusive upper limits
};
/*
* Adds a dimensin with valid range [start, end) to the combinator
*/
void combo_add(Combinator *c, int start, int end)
{
if (c->n < MAX && start < end) {
c->data[c->n] = start;
c->start[c->n] = start;
c->end[c->n] = end;
c->n++;
}
}
/*
* Reset the combinator to the lower limits
*/
void combo_reset(Combinator *c)
{
c->index = 0;
memcpy(c->data, c->start, sizeof(c->start));
}
/*
* Get the next comnination in c->data. Returns 1 if there
* is a next combination, 0 otherwise.
*/
int combo_next(Combinator *c)
{
size_t i = 0;
if (c->index++ == 0) return 1;
do {
c->data[i]++;
if(c->data[i] < c->end[i]) return 1;
c->data[i] = c->start[i];
i++;
} while (i < c->n);
return 0;
}
This implements an odometer-like counter: It increments the first counter. If it overflows, it resets it and increments the next counter, moving to te next counter as needed. If the last counter overflows, the generation of combinations stops. (There's a bit of a kludge with the index for the first combination so that you can control everything from the loop condition of a while loop. There's probably a more elegant way to solve this.)
Use the combinator like this:
Combinator combo = {0}; // Must initialize with zero
combo_add(&combo, 0, 3);
combo_add(&combo, 10, 12);
combo_add(&combo, 4, 7);
while (combo_next(&combo)) {
printf("%4zu: [%d, %d, %d]\n", combo.index,
combo.data[0], combo.data[1], combo.data[2]);
}
This combiinator is designed to use only once: Create it, set up the ranges, then exhaust the combinations.
If you break out of the loop, the combinator retains its state, so that further call to combo_next continue where you broke off. You can start afresh by calling combo_reset. (This is a bit like reading from a file: The usual way to use them is to read everything, but you can rewind.)