c ++错误，“无法推断'std ...”的参数

Question

我的程序总是遇到同样的错误，我们将不胜感激。

错误 1 ​​错误 C2784: 'std::basic_istream<_elem> &std::getline(std::basic_istream<_elem> &,std::basic_string<_elem> &)' : 无法推断 'std::basic_string<_elem> &' 的模板参数来自 'char' c:\Users\esmier\Documents\Visual Studio 2008\Projects\Chapter 4 lab\Chapter 4 lab\source.cpp 40 Chapter 4 lab

错误 2 错误 C2780: 'std::basic_istream<_elem> &std::getline(std::basic_istream<_elem> &,std::basic_string<_elem> &,const _Elem)' : 期望 3 参数 - 2 个提供 c:\Users\esmier\Documents\Visual Studio 2008\Projects\Chapter 4 lab\Chapter 4 lab\source.cpp 40 Chapter 4 lab

注释为 case b 的部分也会发生错误

#include <iostream>
#include<sstream>
int main()
{
double hours;
double Package_A_price=9.95, Package_A_hours=10, Package_A_additional=2.00,Package_A_total;
double Package_B_price=14.95, Package_B_hours=20, Package_B_additional=1.00,Package_B_total;
double Package_C_price=19.95;
char package_choice, additional_hours[3];

//table output

cout<<"Please choose your package below";

cout<<"Package A:\t"<<"For $9.95 per month 10 hours of service are provided.\n";
cout<<"\t\tAdditional hours are $2.00 per hour\n\n";

cout<<"Package B:\t"<<"For $14.95 per month 20 hours of service are provided.\n";
cout<<"\t\tAdditional hours are $1.00 per hour\n\n";

cout<<"Package A:\t"<<"For $19.95 per month unlimited access is provided.\n\n\n";

cout<<"What is your package letter?\n";
cin>>package_choice;
while (package_choice!='A'||'a'||'B'||'b'||'C'||'c')
{
    cout<<"You entered an incorrect option.\n";
    cout<<"please reenter your choice.\n\n";
}
switch (package_choice)
{
//package A choice
case 'A||a':
    cout<<"Did you have any additional hours?\n";
    getline(cin, additional_hours);
    if (additional_hours == 'yes')
    {
        cout<<"How many hours did you have?\n";
        cin>>hours;
        while (hours >744)
        {
            cout<<"You can not have over 744 hours per month!\n";
            cout<<"Time is a linear constant, Please renter your amount.\n";
        }
        Package_A_total=9.95+(2.00*hours);
        cout<<"Your Total for Package A is $"<<Package_A_total;
        break;
    }
//package B choice
case 'B||b':
    cout<<"Did you have any additional hours?\n";
    getline(cin, additional_hours);
    if (additional_hours == 'yes')
    {
        cout<<"How many hours did you have?\n";
        cin>>hours;
        while (hours >744)
        {
            cout<<"You can not have over 744 hours per month!\n";
            cout<<"Time is a linear constant, Please renter your amount.\n";
        }
        Package_B_total=14.95+(1.00*hours);
        cout<<"Your Total for Package B is $"<<Package_B_total;
        break;
    }
//package C choice
case 'C||c':
    cout<<"Your Total for Package C is $"<<Package_B_price;
    break;

default: cout<<"You did not Enter A B or C.\n";
         cout<<"Please reenter your choice.";
}



system ("pause");
    return 0;

}

Answer 1

additional_hours 被声明为 a character 3 个字符的数组。这种形式的 getline 要求您使用 std::string（另一种 C 风格的形式 char* 是 cin 的成员函数）。

还有许多其他错误，显然是因为您不知道 char 表示单个字符：

case 'A||a':
if (additional_hours == 'yes')

那些使用多字节字符常量。基本上它根本不是你所期望的（它是一个用 ASCII 字符或类似字符编码的单个数字）。

while (package_choice!='A','a','B','b','C','c')

同样，这不是您比较多个条件的方式，您需要将其与逻辑与和或（&& 和 ||）结合起来。实际上，它使用逗号运算符，这意味着评估所有操作数并使用最后一个 ('c') 作为结果。

另外，<cctype> 中的 tolower 或 toupper 函数可能会对您有所帮助。

打开编译器警告（-Wall with GCC）可能会显示所有这些错误：[警告]多字符字符常量，[警告]逗号左侧操作数无效，[警告]案例标签值超过最大值对于类型，由于数据类型的范围有限，[警告] 比较总是错误的。

编辑：既然您已将 additional_hours 声明为一个字符数组，您应该知道 3 个字符不足以存储字符串“yes”，因为空终止符没有空间。你最好使用 std::string 类。

Answer 2

我已经看到一个缺陷，您的 while 循环没有重置 package_choice：

while (package_choice!='A','a','B','b','C','c'){       
         cout<<"You entered an incorrect option.\n";        
         cout<<"please reenter your choice.\n\n";
}

您需要再次输入 cin >> 包选择。

Answer 3

试试这个：

cin.getline(additional_hour, 3)

Answer 4

使用std::cout 或std::cin 或std::cin.getline(..) 而不是您正在使用的。

使用std::cin.get() 而不是system("pause") 来固定屏幕

Answer 5

它似乎不喜欢你传递给 getline 的内容。尝试将 additional_hours 声明为 std::string。