Если вы чувствуете необходимость написать это самостоятельно, а не использовать готовую библиотеку, вы можете использовать std::unordered_map<> и добавить поддержку потоковой передачи и извлечения. Вот пример с комментариями в коде:
#include <string>
#include <unordered_map>
class KeyValue { // Key Value
std::unordered_map<std::string, std::string> m_kv{};
public:
// at() is used to get a reference to a Value given the supplied Key. It uses
// the function with the same name in the unordered_map.
inline std::string& at(const std::string& Key) { return m_kv.at(Key); }
inline const std::string& at(const std::string& Key) const { return m_kv.at(Key); }
// The "as<T>" function below is used to extract values from the map.
// The exact version of the function that will be used depends on the type
// you want to extract from the string. Explicit specializations of the function
// are declared outside the class.
// A generic conversion function to anything that can be constructed from a std::string
template<typename T>
T as(const std::string& Key) const {
return at(Key);
}
// A function to extract directly into a variable using the proper as<T>
template<typename T>
void extract_to(T& var, const std::string& Key) const {
var = as<T>(Key);
}
// A friend function to read from an input stream (like an open file) and
// populate the unordered_map.
friend std::istream& operator>>(std::istream&, KeyValue&);
};
// Explicit specializations of KeyValue::as<T>()
// floats
template<>
float KeyValue::as(const std::string& Key) const {
return std::stof(at(Key));
}
template<>
double KeyValue::as(const std::string& Key) const {
return std::stod(at(Key));
}
template<>
long double KeyValue::as(const std::string& Key) const {
return std::stold(at(Key));
}
// signed integers
template<>
int KeyValue::as(const std::string& Key) const {
return std::stoi(at(Key));
}
template<>
long KeyValue::as(const std::string& Key) const {
return std::stol(at(Key));
}
template<>
long long KeyValue::as(const std::string& Key) const {
return std::stoll(at(Key));
}
// unsigned integers
template<>
unsigned KeyValue::as(const std::string& Key) const {
return std::stoul(at(Key));
}
template<>
unsigned long KeyValue::as(const std::string& Key) const {
return std::stoul(at(Key));
}
template<>
unsigned long long KeyValue::as(const std::string& Key) const {
return std::stoull(at(Key));
}
// bool
template<>
bool KeyValue::as(const std::string& Key) const {
const std::string& val = at(Key);
if(val=="true" || val=="1") return true;
else if(val=="false" || val=="0") return false;
throw std::range_error("\"" + Key + "\" is neither true nor false");
}
// the friend function that extracts key value strings from a stream
std::istream& operator>>(std::istream& is, KeyValue& kv) {
std::string line;
// read one line at a time
while(std::getline(is, line)) {
auto pos = line.find('=');
if(pos == std::string::npos || pos == 0) {
// if '=' was not found (or found at pos 0), set the failbit on the stream
is.setstate(std::ios::failbit);
} else {
// if '=' was found, put the Key and Value in the map by
// using substr() to split the line where the '=' was found
kv.m_kv.emplace(line.substr(0, pos), line.substr(pos + 1));
}
}
return is;
}
Имея это в виду, вы можете прочитать файл и заполнить переменные, которые вы предпочтительно поместили в class / struct. Пример:
#include <fstream>
struct Variables {
std::string Name{};
unsigned int Age{};
std::string Gender{};
double PI{};
bool Hungry{};
bool Sad{};
Variables(const std::string& filename) {
std::ifstream is(filename);
if(is) {
KeyValue tmp;
is >> tmp; // stream the whole file into tmp
// extract values
tmp.extract_to(Name, "Name");
tmp.extract_to(Age, "Age");
tmp.extract_to(Gender, "Gender");
tmp.extract_to(PI, "PI");
tmp.extract_to(Hungry, "Hungry");
tmp.extract_to(Sad, "Sad");
} else throw std::runtime_error("Could not read \""+filename+"\".");
}
};
Пример файла данных (vars.dat):
Name=No name
Age=8
Gender=male
PI=3.14159
Hungry=true
Sad=false
... и основной пример ::
#include <iostream>
int main() {
try {
Variables var("vars.dat"); // open file and populate variables
std::cout << std::boolalpha
<< "Name: " << var.Name << "\n"
<< "Age: " << var.Age << "\n"
<< "Gender: " << var.Gender << "\n"
<< "PI: " << var.PI << "\n"
<< "Hungry: " << var.Hungry << "\n"
<< "Sad: " << var.Sad << "\n";
} catch(const std::exception& ex) {
std::cerr << ex.what() << "\n";
}
}