如果每个 cin 输入多个单词，如何禁止 cin 转发到下一个输入？答案

【问题标题】：How do I disallow cin from forwarding to the next input if I enter more than one word per cin?如果每个 cin 输入多个单词，如何禁止 cin 转发到下一个输入？
【发布时间】：2015-06-15 16:58:45
【问题描述】：

在该程序的每个输入中，我希望用户能够输入他们想要的任意数量的“单词”（意思是由空格/制表符分隔的文本）......但不允许用户输入单词超出当前的 cin。例如：如果我输入 John Smith Doe，我希望将 John 放入“name”中，并丢弃 Smith 和 Doe。然后我想输入“年龄”和“体重”，而不需要让 Smith 变老而 Doe 变重。目前，如果我输入 John Doe 作为名称，那么年龄将变为 Doe。如果我输入 John Smith Doe 作为名称，则年龄变为 Smith，体重变为 Doe。有人可以帮忙吗？

#include <iostream>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
    string name;
    string age;
    string weight;

    //user can enter more than one name (title, first, middle, last, etc.)
    cout << "Enter your name: " << endl;
    cin >> name;

    //if user entered two or more names above,
    //disallow cin from putting name two into 'age'
    cout << "Enter your age: " << endl;
    cin >> age;

    //same thing for weight
    cout << "Enter your weight: " << endl;
    cin >> weight;

    cout << "You typed: " << endl;
    cout << "Name: " << name << endl;
    cout << "Age: " << age << endl;
    cout << "Weight: " << weight << "." << endl;

    return 0;
}

【问题讨论】：

你想要 std::getline(stream, string)
你只需ignore它。
当您的代码提示输入姓名时，您的代码是否跳过了“标题”输入？为什么您的 cmets 使用“first”、“middle”、“last”而不是“name”？也许你的提示是不够的。你能改进你的需求陈述吗？
这是最好的答案...特别是：getline(stream, string)。

标签： c++

【解决方案1】：

我认为你可以使用

std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

例如在cin >> name;之后。

【讨论】：

沿着这些思路，但更标准一些cin.ignore(std::numeric_limits<std::streamsize>::max())
这将跳过一行，如果换行符跟在 'name' 后面
@DieterLücking，你是对的。我将编辑我的答案

【解决方案2】：

逐行读取流，将每一行传递给 istingstream 并读取感兴趣的字段：

// Read Fields [Teminating State]
inline std::istream& read_fields(std::istringstream& line_stream)
{
    return line_stream;
}

// Read Fields
template <typename Arg, typename ... Args>
inline std::istream& read_fields(std::istringstream& line_stream, Arg& arg, Args&... args)
{
    if(line_stream >> arg)
        read_fields(line_stream, args...);
    return line_stream;
}

// Read and Skip Fields of a Line
template <typename ... Args>
std::istream& read_line(std::istream& stream, Args& ... args)
{
    std::string line;
    if(std::getline(stream, line)) {
        std::istringstream line_stream(line);
        read_fields(line_stream, args...);
        if(line_stream.fail()) {
            // Pass the fail state to the stream.
            stream.setstate(std::ios_base::failbit);
        }
    }
    return stream;
}

// Test
int main()
{
    std::string name;
    read_line(std::cin, name);

    std::string age;
    std::string weight;
    read_line(std::cin, age, weight);

    if(std::cin)
        std::cout << "Name: " << name << ", Age: " << age << "Weight: " << weight << '\n';
    else
        std::cout << "Failure\n";
    return 0;
}

【讨论】：

【解决方案3】：

这是我开发的解决方案。感谢您的帮助！

string name;
string age;
string weight;

cout << "Enter your name: " << endl;
//this line allows me to take in a full line (up
//to the newline character) at once
getline(cin, name);
//then i search for the first occurence of a 
//spacebar, or output the whole line if none
//is found
int i = 0;
int len = name.length();
for(; i < len; i++)
{
    if(name[i] == ' ')
    {
        break;
    }
}
//chop off end of variable 'name'
//after first spacebar or leave 
//it whole if no spacebar was
//found
name = name.substr(0, i);

//same thing as above for here
cout << "Enter your age: " << endl;
getline(cin, age);
i = 0;
len = age.length();
for(; i < len; i++)
{
    if(age[i] == ' ')
    {
        break;
    }
}
age = age.substr(0, i);

//ditto for here
cout << "Enter your weight: " << endl;
getline(cin, weight);
i = 0;
len = weight.length();
for(; i < len; i++)
{
    if(weight[i] == ' ')
    {
        break;
    }
}
weight = weight.substr(0, i);

cout << "You typed: " << endl;
cout << "Name: " << name << endl;
cout << "Age: " << age << endl;
cout << "Weight: " << weight << endl;

【讨论】：