Cin 不等待输入

Question

这是程序：

#include <iostream>
#include <string>
#include <stdlib.h>


using namespace std;

int main(){


string strKingdom = "";
bool conquered_me;//see if was conquered, was going to use this on other program and true = game over.
int gold;
int food;
int citizens;
int soldiers;



cout << endl <<"Name of kingdom: ";
cin >> strKingdom;
cout << endl << "were you conquered (true/false): ";
cin >> conquered_me;
cout << endl << "How many gold do you have?:";
cin>>gold;
cout << endl << "How many food do you have?:";
cin >> food;
cout << endl << "How many citizens do you have?:";
cin >> citizens;
cout << endl << "How many soldiers do you have?:";
cin >> soldiers;


return 0;
}

问题是，当我编译它时，程序只允许我插入前 2 个变量，然后它会显示其余的问题（编译后）：

王国名称：史蒂夫

你被征服了吗（真/假）：假

你有多少金币？： 你有多少食物？： 你有多少公民？： 你有多少士兵？：

Answer 1

在bool 变量中输入字符串“true”不起作用。您应该输入1 或0。你的“真实”不能被“消费”，所以它留在缓冲区中。接下来，您尝试读取int 值，因此“true”也不匹配。以此类推……直到程序结束。

我就是这样做的：

#include <string>
#include <iostream>

#include <errno.h>
#include <stdlib.h>

using namespace std;

void askForString(string aPrompt, string &aValue) {
    cout << aPrompt << " ";
    cin >> aValue;
}

void askForBool(string aPrompt, bool &aValue) {
    string tString;
    while (1) {
        cout << aPrompt << " ";
        cin >> tString;
        if (tString == "true") {
            aValue = true;
            break;
        } else if (tString == "false") {
            aValue = false;
            break;
        } else {
            cout << "Repeat, please?" << endl;
        }
    }
}

void askForInt(string aPrompt, int &aValue) {
    string tString;
    char *endptr;
    while (1) {
        cout << aPrompt << " ";
        cin >> tString;
        errno = 0;
        aValue = strtol(tString.c_str(), &endptr, 10);
        if (errno || tString.c_str() == endptr || (endptr != NULL && *endptr != 0)) {
            cout << "Repeat, please?" << endl;
        } else {
            break;
        }
    }
}

int main(void) {
    string strKingdom;
    bool conquered_me;
    int gold;
    int food;
    int citizens;
    int soldiers;

    askForString("Name of kingdom:", strKingdom);

    askForBool("were you conquered (true/false):", conquered_me);

    askForInt("How many gold do you have?:", gold);

    askForInt("How many food do you have?:", food);

    askForInt("How many citizens do you have?:", citizens);

    askForInt("How many soldiers do you have?:", soldiers);

    cout << "Kingdom: " << strKingdom << endl;
    cout << "Conquered: " << (conquered_me ? "true" : "false") << endl;
    cout << "Gold: " << gold << endl;
    cout << "Food: " << food << endl;
    cout << "Citizens: " << citizens << endl;
    cout << "Soldiers: " << soldiers << endl;

    return 0;
}

Answer 2

将它们全部转换为字符串，并根据需要进行转换。

Answer 3

出于某种原因（可能与旧代码兼容）iostreams 默认在 I/O 期间将 true 转换为 1 和 false 转换为 0。

这只是默认设置 - 有一个名为 boolalpha 的操纵器会将流设置为使用 true 和 false（或本地化等效项）。

所以，代码如下：

std::cout << 1 == 0;               // produces `0`
std::cout << boolalpha << 1 == 0;  // produces `false`

这也适用于输入，因此您可以将代码更改为以下内容：

cin >> boolalpha >> conquered_me;

...它应该按预期工作（并且在：它应该接受false 或true 的输入，并从它们产生false 和true 的值，如果不是这样标准库中的错误）。

Answer 4

您的所有读取命令都不会检查错误。所有这些都应该写成这样的：

while (!(std::cin >> strKingdom)) {
    std::cerr << 'Bad input' << std::endl;
    std::cin.clear();  // clear the error
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');  // ignore the rest of the line
    // output the same prompt again?
}

为了使这更容易，您可能需要编写一个辅助函数：

template<typename T> void get_input(const char *prompt, T &result) {
    std::cout << prompt << std::endl;
    while (!(std::cin >> result)) {
        std::cerr << 'Bad input' << std::endl;
        std::cin.clear();
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
        std::cout << prompt << std::endl; } }

然后您可以专门为 bool 类型正确读取 true/false...

Answer 5

这一行：

cin >> conquered_me;

应该是这样的：

cin >> boolalpha >> conquered_me;

否则输入需要“0”或“1”。

通过使用boolalpha，您的输入可以是“真”或“假”。

Answer 6

您需要使用 std::getline 和 std::string 来读取各种值。 （然后您可以使用 atoi 之类的函数来解析它们。）这是您使用 std::getline 函数的代码示例。

#include <iostream>
#include <string>
#include <cstdlib>

int main(){


std::string strKingdom = "";
bool conquered_me;//see if was conquered, was going to use this on other program and true = game over.
int gold;
int food;
int citizens;
int soldiers;

std::string tString = ""; // Used to read and subsequently parse the string.


std::cout << std::endl <<"Name of kingdom: ";
std::getline(std::cin,strKingdom);

std::cout << std::endl << "were you conquered (true/false): ";
std::getline(std::cin,tString);
conquered_me = (tString == "true");

std::cout << std::endl << "How many gold do you have?:";
std::getline(std::cin,tString);
gold = std::atoi(tString.c_str());

std::cout << std::endl << "How many food do you have?:";
std::getline(std::cin,tString);
food = std::atoi(tString.c_str());

std::cout << std::endl << "How many citizens do you have?:";
std::getline(std::cin,tString);
citizens = std::atoi(tString.c_str());

std::cout << std::endl << "How many soldiers do you have?:";
std::getline(std::cin,tString);
soldiers = std::atoi(tString.c_str());


return 0;
}