Sortowanie struktur w plikach

sort.cpp

#include <iostream>
#include <fstream>
#include <string.h>

using namespace std;


int cmp_char_arr(const char* a, const char* b, int size_a, int size_b) {
	int min_size = size_a < size_b ? size_a : size_b;
	for (int i = 0; i < min_size; i++) {
		if (a[i] > b[i]) {
			return -1;
		} else if (a[i] < b[i]) {
			return 1;
		}
	}
	return 0;
}

struct my_struct {
	char name[80];
};

void write_initial_data() {
	fstream file("my_database.dat", ios::binary | ios::out | ios::in | ios::app);

	my_struct a;

	strncpy(a.name, "BAA", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "AAA", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "CCC", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "BBB", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "AAB", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "ABA", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "ABA", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "BAA", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	strncpy(a.name, "AAA", sizeof(a.name));
	file.write(reinterpret_cast<char*>(&a), sizeof(a));

	file.close();
}

void display_file() {

	fstream file("my_database.dat", ios::binary | ios::out | ios::in);

	file.seekg(0);
	if (!file.eof()) {
		for (;;) {
			my_struct a;
			file.read(reinterpret_cast<char*>(&a), sizeof(a));
			if (file.eof()) break;
			cout << a.name << endl;
		}
	}
}
void sort_struct_in_file() {
	fstream file("my_database.dat", ios::binary | ios::out | ios::in | ios::ate);

	my_struct a;
	my_struct b;

	file.seekg (0, file.end);
	int length = file.tellg();
	file.seekg (0, file.beg);

	int size = length / sizeof(a);
	for ( int i = 0; i < size; i++ ) {
		for ( int j = 0; j < size - 1; j++ ) {
			file.seekg(sizeof(struct my_struct) * ( j ));
			file.read(reinterpret_cast<char*>(&a), sizeof(a));

			file.seekg(sizeof(struct my_struct) * ( j + 1));
			file.read(reinterpret_cast<char*>(&b), sizeof(b));
			int cmp_result = cmp_char_arr(a.name, b.name, sizeof(a.name), sizeof(b.name));
			// cout << a.name << " = " << b.name << " = " << cmp_result << endl;
			if (cmp_result < 0) {
				// cout << a.name << "<=>" << b.name << endl;

				file.seekp(sizeof(struct my_struct) * ( j ));
				file.write(reinterpret_cast<char*>(&b), sizeof(b));

				file.seekp(sizeof(struct my_struct) * ( j + 1));
				file.write(reinterpret_cast<char*>(&a), sizeof(a));
			}
		}
	}
	file.close();
}

int main() {
	write_initial_data();
	cout << "Plik: " << endl;
	display_file();
	sort_struct_in_file();
	cout << "Plik po:" << endl;
	display_file();
}