这行在代码中做什么

我在网上为后缀树找到了以下代码

#include <stdio.h>
#define E 0
struct suffix_tree_node;

struct suffix_tree_link {
    // 0 is e - global index of during string's end
    unsigned long start;
    unsigned long end;
    suffix_tree_link(suffix_tree_node* source, suffix_tree_node* target, 
                     unsigned long start, unsigned long end) {
        this->source = source;
        this->target = target;
        this->start = start;
        this->end = end;
    }
    suffix_tree_node* source;
    suffix_tree_node* target;
    suffix_tree_link* next_link;
};
struct suffix_tree_node {
    suffix_tree_link* first_link;
    suffix_tree_node* parent_node;
    suffix_tree_node* suffix_link_node;
    // other constructors?
    suffix_tree_node() {
        parent_node = suffix_link_node = NULL;
        first_link = NULL;
    }
    void add_target(unsigned long start, unsigned long end, suffix_tree_node* target) {
        suffix_tree_link* link;
        for(link = first_link; link != NULL; link = link->next_link);
        link = new suffix_tree_link(this, target, start, end);
    }
};

class suffix_tree {
    suffix_tree_node* root;
    const char* string;
    void ukkonen() {
        root->add_target(1, E, new suffix_tree_node);
        unsigned long e = 1, j_i = 1, i = 1; 
        for( int i = 0; string[i] != ''; i++) {
            e++;
            for() {
                j_star = j;
            }
            j_i = j_star;
        }
    }
public:
    suffix_tree(const char* string) {
        root = new suffix_tree_node();
        this->string = string;
        ukkonen();
    }
};
int main() {
    suffix_tree("foof");
    return 0;
}

在这段代码中，一切都很清楚，因为我以前读过很多次后缀树，但我不理解这个片段：

void ukkonen() {
            root->add_target(1, E, new suffix_tree_node);
            unsigned long e = 1, j_i = 1, i = 1; 
            for( int i = 0; string[i] != ''; i++) {
                e++;
                for() {
                    j_star = j;
                }
                j_i = j_star;
            }
        }

这个代码的作用是什么？

什么是for()？还是CCD_ 2？

这是这个代码的链接。