c++ - 尝试在 Vector 中查找内容时出错，不确定如何修复

Question

所以我有一个 .txt 文件，我正在将其推送到一个 vector 中，并且一切正常。我正在尝试获取用户输入(字符串)，并在 vector 中找到匹配项。到目前为止，这是我的代码:

#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <list>

using namespace std;

struct customer{
  string name;
  float disc;
};

class customer_list {
  vector<customer> custlist;

public:
  void load(string fname){
   ifstream list;
   list.open ("customers.txt");
   customer c;
   double val = 0;
   if (list.is_open()){
     while (! list.eof() ){
       list >> c.name;
       custlist.push_back(c);
       list >> c.disc;
       custlist.push_back(c);
       val++;
     }
   }
     list.close();
     int val2 = custlist.size()/val;

     for (int j=0; j < custlist.size() - 2; j+= val2){
         cout << " Name: " << custlist[j].name << endl;
         cout << " Discount: " << custlist[j+1].disc << endl;
     }
  }


bool in_list(string & query){ //return true if query in list, false otherwise
  if (find (custlist.begin(), custlist.end(), query) !=custlist.end()){
    cout << "Welcome back," << query << "." <<endl;
    return true;
  }else{
    cout << "No Matches found." << endl;
    return false;
  }
 }
};

int main (){

customer_list a;
string name;

a.load("customers.txt");

cout << "What is your name?" << endl;
cin >> name;

a.in_list(name);
}

运行时出现这个错误:

In file included from prt2.cpp:1:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/iostream:38:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/ios:216:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:439:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/algorithm:865:22: error: invalid operands
      to binary expression ('customer' and 'const std::__1::basic_string<char>')
        if (*__first == __value_)
            ~~~~~~~~ ^  ~~~~~~~~
prt2.cpp:46:15: note: in instantiation of function template specialization 'std::__1::find<std::__1::__wrap_iter<customer *>,
      std::__1::basic_string<char> >' requested here
          if (find (custlist.begin(), custlist.end(), query) !=custlist.end()){
              ^
1 error generated.

感谢任何帮助!谢谢。

Answer 1

您的查找 正在将苹果与橙子进行比较。使用 std::find 寻找的搜索值必须与序列的类型相同或可转换为序列的类型，这并非严格正确，但通常是实践中的。您可以使用比较两个值的等价运算符 (operator ==) 来避免这种情况，即使它们是不同的类型，但实际上不需要这种疯狂。无论如何，您要在充满 customer 的丛林中搜索 std::string。

您可以使用其他搜索方法来解决这个问题，例如 std::find_if 和自定义限定 lamda 表达式:

像这样:

bool in_list(const string & s)
{
    if (std::find_if(custlist.begin(), custlist.end(),
            [&s](const customer& c) { return c.name == s; }) != custlist.end())
    {
        cout << "Welcome back," << s << "." <<endl;
        return true;
    }

    cout << "No Matches found." << endl;
    return false;
}

当然还有其他方法。

无论如何，祝你好运。