utils-std

relative_path.c (1109B)

// utils-std: Collection of commonly available Unix tools
// SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
// SPDX-License-Identifier: MPL-2.0
#define _POSIX_C_SOURCE 200809L
#include "./relative_path.h"
#include <string.h>
int
relative_path(const char *base, const char *abs_file, char result[static PATH_MAX])
{
	if(!base[0] || !abs_file[0]) return -1;
	int comm = 0;
	for(int i = 0; base[i] && abs_file[i]; i++)
	{
		if(base[i] != abs_file[i]) break;
		if(base[i] == '/') comm = i;
	}
	comm++;
	// both paths pointing to the same directory
	if(base[comm] == '\0' && abs_file[comm] == '\0')
	{
		result[0] = '.';
		result[1] = '\0';
		return 0;
	}
	size_t abs_rem = strlen(abs_file + comm);
	int off = 0;
	for(int i = comm; base[i]; i++)
		if(base[i] == '/') off++;
	// Make sure everything fits before copying into result
	if(((off * 3) + abs_rem + 1) > PATH_MAX) return -1;
	int res_pos = 0;
	for(int i = 0; i < off; i++)
	{
		memcpy(result + res_pos, "../", 3);
		res_pos += 3;
	}
	memcpy(result + res_pos, abs_file + comm, abs_rem + 1);
	return 0;
}