error: no match for 'operator==' and template argument deduction/substitution failed:

Question

此刻只是有点沮丧。作为 C++ 菜鸟的乐趣。使用 g++ 编译器。在搜索功能中，我在第 54 行发现了几个错误。下面是前两个，因为我知道这都与一两个我目前看不到的错误有关。

ghp1.cpp: In function 'int search(std::string*, int)':
ghp1.cpp:54:22: error: no match for 'operator==' (operand types are 'std::string {aka std::basic_string}' and 'int')
if (casino[area] == area)
                 ^
ghp1.cpp:54:22：注意：候选人是：
在 /usr/local/lib/gcc48/include/c++/iosfwd:40:0,
包含的文件中来自 /usr/local/lib/gcc48/include/c++/ios:38,
来自 /usr/local/lib/gcc48/include/c++/ostream:38,
来自 /usr/local/lib/gcc48/include/c++/iostream:39,
来自 ghp1.cpp:7:
/usr/local/lib/gcc48/include/c++/bits/postypes.h:216:5: 注意：模板 bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT >&)
operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
^
/usr/local/lib/gcc48/include/c++/bits/postypes.h:216:5: 注意：模板参数 deduction/substitution 失败：
ghp1.cpp:54:25: 注意：'std::string {aka std::basic_string}' 不是派生自 'const std::fpos<_StateT>'
if (casino[area] == area)
                    ^

下面是我的程序的代码，它应该进行搜索并在函数中显示结果（在 main() 之外）。

 1  #include <iostream>
 2  #include <cstring>
 3
 4  using namespace std;
 5
 6  int search (string casino[ ], int area);        //Prototype
 7
 8  int main(void)
 9  {
10  int i=0;
11  string casino[11];                              //Creates array
12
13  casino[1] = "Alpha";                            //Fills array
14  casino[2] = "Bravo";
15  casino[3] = "Charlie";
16  casino[4] = "Delta";
17  casino[5] = "Echo";
18  casino[6] = "Foxtrot";
19  casino[7] = "Golf";
20  casino[8] = "Hotel";
21  casino[9] = "India";
22  casino[10] = "Juno";
23
24  /*Query user for search value*/
25
26  cout<<"     This program will help you find the first ten gaming zones of ";
27  cout<<"a casino."<<endl;
28  cout<<"Pick a number between 1 and 10: "<<endl;
29  cin>>i;
30
31  cout<<"     This program will help you find the first ten gaming zones of ";
32  cout<<"a casino."<<endl;
33  cout<<"Pick a number between 1 and 10: "<<endl;
34  cin>>i;
35
36  /*Call Search Function & Display of Result*/
37
38  search(casino, i);
39
40  cout<<"    *** Good Bye! ***"<<endl;
41
42  return 0;
43  }
44
45
46  int search (string casino[ ], int area)
47  {
48  string result;
49  bool answer;
50  answer=false;
51 
52  while ((area <= 10) && (!answer))
53     {                               //Check if number is in search area.
54     if (casino[area] == area)       //***BAD LINE***//
55         answer=true;
56     else
57         area++;
58     }
59  if (answer)
60     cout<<" That zone is named: "<<casino[area]<<endl;
61  else                                 //Display of incorrect input.
62     cout<<" Nice try smartie pants!"<<endl;
63     cout<<" I said, between 1 and 10."<<endl;
64 
65  return 0;
66  }

Answer 1

其实问题很简单。编译器抱怨 not "know" about any operator==(...) overload for comparing string and int:

casino[area] == area  // bad string

casino 是一个字符串数组，所以 casino[area] 是一个字符串，而 area 是一个整数。您的函数搜索应该期待一个字符串作为第二个参数：

int search (string casino[ ], string area)

Answer 2

您比较的是字符串和整数。没有为此定义运算符重载，因此编译器报错。

也许你想要这个

#include <iostream>
#include <cstring>

using namespace std;

void search (string casino[ ], int casinolen, unsigned int area);        //Prototype

int main(int, char**)
{
    unsigned int i=0;
    string casino[10];                              //Creates array

    casino[0] = "Alpha";                            //Fills array
    casino[1] = "Bravo";
    casino[2] = "Charlie";
    casino[3] = "Delta";
    casino[4] = "Echo";
    casino[5] = "Foxtrot";
    casino[6] = "Golf";
    casino[7] = "Hotel";
    casino[8] = "India";
    casino[9] = "Juno";

    /*Query user for search value*/

    cout<<"     This program will help you find the first ten gaming zones of ";
    cout<<"a casino."<< endl;
    cout<<"Pick a number between 1 and 10: "<<endl;
    cin>>i;

    /*Call Search Function & Display of Result*/

    search(casino, 10, i);

    cout << "    *** Good Bye! ***" << endl;

    return 0;
}

void search (string casino[ ], int casinolen, unsigned int area)
{
    if (area > 0 && area <= casinolen)
    {
        cout<<" That zone is named: "<<casino[area-1]<<endl;
    }
    else
    {//Display of incorrect input.
        cout<<" Nice try smartie pants!"<<endl;
        cout<<" I said, between 1 and " << casinolen << "."<<endl;
    }
}

您可以输入 1 到 10 之间的数字，它会打印相关赌场的名称。

它将数组的长度（此处硬编码，但可以使用 sizeof 获得）传递给搜索函数，以了解您输入的数字是否在数组的范围内。当你想输入 1-10 时它被移动 1，而数组索引实际上是 0-9.

传递长度是 C 中常用的一种方法。对于 C++，您最好使用 vector，它使用其 size 方法知道自己的长度。

error: no match for 'operator==' and template argument deduction/substitution failed:

error: no match for 'operator==' and template argument deduction/substitution failed:

c++

function

while-loop