vector_io.h

#ifndef VECTOR_IO_H
#define VECTPR_IO_H

#include <string>
#include <vector>
#include <stdexcept>
#include <fstream>

template<class T>
void save_vector(const std::string&file_name, const std::vector<T>&vec){
	std::ofstream out(file_name, std::ios::binary);
	if(!out)
		throw std::runtime_error("Can not open \""+file_name+"\" for writing.");
	out.write(reinterpret_cast<const char*>(&vec[0]), vec.size()*sizeof(T));
}

template<class T>
std::vector<T>load_vector(const std::string&file_name){
	std::ifstream in(file_name, std::ios::binary);
	if(!in)
		throw std::runtime_error("Can not open \""+file_name+"\" for reading.");
	in.seekg(0, std::ios::end);
	unsigned long long file_size = in.tellg();
	if(file_size % sizeof(T) != 0)
		throw std::runtime_error("File \""+file_name+"\" can not be a vector of the requested type because it's size is no multiple of the element type's size.");
	in.seekg(0, std::ios::beg);
	std::vector<T>vec(file_size / sizeof(T));
	in.read(reinterpret_cast<char*>(&vec[0]), file_size);
	return vec; // NVRO
}

template<>
void save_vector<std::string>(const std::string&file_name, const std::vector<std::string>&vec){
	std::ofstream out(file_name, std::ios::binary);
	for(unsigned i=0; i<vec.size(); ++i){
		const char*x = vec[i].c_str();
		out.write(x, vec[i].length()+1);
	}
}

template<>
std::vector<std::string>load_vector<std::string>(const std::string&file_name){
	std::vector<char>data = load_vector<char>(file_name);
	std::vector<std::string>ret;
	std::vector<char>::const_iterator 
		str_begin = data.begin(), 
		str_end = data.begin(), 
		data_end = data.end();

	while(str_end != data_end){
		if(*str_end == '\0'){
			ret.push_back(std::string(str_begin, str_end));
			++str_end;
			str_begin = str_end;
		}else{
			++str_end;
		}
	}

	ret.shrink_to_fit();
	return ret; // NVRO
}

template<class T>
void save_value(const std::string&file_name, const T&val){
	save_vector(file_name, std::vector<T>{val});
}

template<class T>
T load_value(const std::string&file_name){
	auto v = load_vector<T>(file_name);
	if(v.empty())
		throw std::runtime_error(file_name+" is empty");
	if(v.size() > 1)
		throw std::runtime_error(file_name+" contains more than one element");
	return v.front();
}

#endif