我有一个用逗号分隔的值的文件
M,21,Hazel
F,49,Stephen
我正在将ifstream发送到使用istream读取行的函数中。
ifstream file(fileName);
char gender;
file.get(gender);
file.ignore(); // ignore comma
if (gender == 'M') {
Gender* tmp = new Male;
file >> *tmp;
} else if (gender == 'F') {
Gender* tmp = new Female;
file >> *tmp;
}
逗号前的第一个字符已正确读取,但是当我发送它以读取时,它会在不需要时要求用户输入。它不会读取文件的其余部分,即“ 49,Stephen”
istream& operator>>(istream& istr, ReadW& ref) {
return ref.read(istr);
}
istream& read(istream& is) {
char tName[16];
is >> age;
is.ignore(); // ignore comma
is.getline(tName, 16, ',');
}
基本上,您是在问有关读取csv文件并将其拆分为令牌的问题。如果在SO上搜索此内容,您会发现很多帖子,其中解释了如何操作。
但是您的情况可能更简单。如果保证源文件的格式完全正确,并且在逗号前后没有多余的空格,则可以对流使用标准的提取器机制。您只需将逗号读入虚拟变量即可。可能看起来像:
// What we want to read
char gender{};
unsigned int age{};
std::string name{};
// This is a dummy
char comma{};
while (testDataStream >> gender >> comma >> age >> comma >> name) {
这将读取变量gender
中的第一个字符,然后读取逗号并将其放入comma
变量中。我们根本不会使用。然后,我们将继续以相同的方式提取更多的值。
如果源文件的结构不同,它将无法正常工作。例如,如果第一个变量是std::string
,则testDataStream >> someString
将读取直到下一个空格的完整行。但是,使用现有结构,它会起作用。
无论如何,您也可以使用其他功能,以防输入线格式不正确。也就是说,首先读取完整的一行,然后将其放入std::istringstream
并从中提取数据。
如果您具有完全不同的数据结构,则可能会将该方法与带分隔符的std::getline
或std::regex_token_iterator
一起使用。但这在这里就足够了。
此外,您显然具有班级等级。然后根据运行时读取的值创建派生类。这通常可以通过Abstract Factory模式解决。
我创建了一个可行的示例,您可以在其中看到所有这些机制。请注意:我将not使用纯C样式char
数组作为字符串。并且,我将从不将原始指针用于拥有的内存。为此,应使用智能指针。
#include <iostream>
#include <sstream>
#include <memory>
#include <map>
#include <functional>
std::istringstream testDataStream(R"(F,21,Hazel
M,49,Stephen)");
// Abstract base class "Person"
struct Person {
// Constructor
Person(const unsigned int a, const std::string& n) : age(a), name(n) {}
// Do not forget the virtual destructor
virtual ~Person() { std::cout << "Destructor Base\n\n\n"; }
// The data: name and age
unsigned int age{};
std::string name{};
// Since the inserter is not none member function, we will write
// a separate virtual function to do the job polymorph
virtual std::ostream& output(std::ostream& os) const = 0;
// Inserter, will call our internal output function
friend std::ostream& operator << (std::ostream& os, const Person& p) {
return p.output(os);
}
};
// Derived class for a male Person
struct Male : public Person {
// Constructor
Male(const unsigned int age, const std::string& name) : Person(age, name) {}
virtual ~Male() { std::cout << "Destructor Male\n"; }
// And output
virtual std::ostream& output(std::ostream& os) const override {
return os << "Male Person:\nAge:\t" << age << "\nName:\t" << name << '\n';
}
};
// Derived class for a female Person
struct Female : public Person {
// Constructor
Female(const unsigned int age, const std::string& name) : Person(age, name) {}
virtual ~Female() { std::cout << "Destructor Female\n"; }
// And output
virtual std::ostream& output(std::ostream& os) const override {
return os << "Female Person:\nAge:\t" << age << "\nName:\t" << name << '\n';
}
};
// "Creation" Functions for abstract factory
std::unique_ptr<Person> createMale(const unsigned int age, const std::string& name) { return std::make_unique<Male>(age, name); }
std::unique_ptr<Person> createFemale(const unsigned int age, const std::string& name) { return std::make_unique<Female>(age, name); }
// Abstract factory
struct AbstractFactory {
// Abbreviation for finding
using Map = std::map<char, std::function<std::unique_ptr<Person>(const unsigned int, const std::string&)>>;
Map creationFunctions{
{'F', createFemale },
{'M', createMale }
};
std::unique_ptr<Person> create(const char selector, const unsigned int age, const std::string& name) {
// If the selector is in the map
if (Map::iterator searchResult{ creationFunctions.find(selector) }; searchResult != creationFunctions.end())
// Then we call the corresponding creation function
return creationFunctions[selector](age, name);
else
// No key found, the return nullptr (Empty Person());
return std::unique_ptr<Person>();
}
};
// Our abstract factor
AbstractFactory abstractFactory{};
// Driver code
int main() {
// What we want to read
char gender{};
unsigned int age{};
std::string name{};
// This is a dummy
char comma{};
std::string line{};
//#define DIRECT_READ
#ifdef DIRECT_READ
// As long as there is data in the stream, read the gender and the comma
while (testDataStream >> gender >> comma >> age >> comma >> name) {
#else
while (std::getline(testDataStream, line)) {
std::istringstream iss{ line };
if (iss >> gender >> comma >> age >> comma >> name) {
#endif
// Create a Person, either male or female
std::unique_ptr<Person> person = abstractFactory.create(gender, age, name);
// Polymorphism. Call the adequate member function
std::cout << *person << '\n';
// Do other stuff
// . . .
}
#ifndef DIRECT_READ
}
#endif
return 0;
}