调试断言失败:字符串下标超出范围

Question

我正在尝试学习编码，并正在创建一个二进制搜索程序。在尝试运行我的代码时，当我尝试调用搜索函数时，我得到一个调试断言失败(参见下面的调试输出)。我搞砸了什么?

#include<iostream>
#include<string>
using namespace std;
const int N = 100;
string names[N];
string query;
//function to search for names in the list
string search(int largestNum, int smallestNum, string names, string query);

int main(){
    cout << "Please enter the names, pressing enter after each entry." << endl 
        << "Type done when you are finished the list" << endl
        << "1.";
    cin >> names[0];
    int ticker1 = 1;
    /*this loop outputs a number 1 greater then the last and allows the 
    user to enter a new name until they type "done" which will exit the loop*/
    do {
        cout << endl << ticker1 + 1 << ".";
        cin >> names[ticker1];
        ticker1++;
    } while ((names[ticker1 - 1] != "done") && (names[ticker1 - 1] != "Done"));
    cout << endl;
    int ticker2 = 0;
    while (ticker2 < (ticker1 - 1)){
        cout << ticker2 + 1 << "." << names[ticker2] << endl;
        ticker2++;
    }
    int largestNum = ticker1;
    int smallestNum = 0;
    cout << "Please Enter the name that you would like to search for:";
    cin >> query;
    cout << search(largestNum, smallestNum, names[N], query);
    return 0;
}
//function to search for names in the list
string search(int largestNum, int smallestNum, string names, string query){
    string middleName;
    int middle = ((largestNum - smallestNum) / 2);
    middleName = names[middle];
    cout << middleName;
    if (query == middleName) return { "Present", "Location:" + middle };
    else return { "Not around" };
}

调试输出

'Learning C++.exe' (Win32): Loaded 'C:UsersGarethProgrammingProjectsLearning C++DebugLearning C++.exe'. Symbols loaded.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64ntdll.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64kernel32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64KernelBase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64msvcp120d.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64msvcr120d.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64user32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64gdi32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64imm32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64msctf.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64msvcrt.dll'. Cannot find or open the PDB file.
Debug Assertion Failed!
Program: C:WindowsSYSTEM32MSVCP120D.dll
File: c:program files (x86)microsoft visual studio 12.0vcincludexstring
Line: 1685
Expression: string subscript out of range
For information on how your program can cause an assertion
failure, see the Visual C++ documentation on asserts.
(Press Retry to debug the application)
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64uxtheme.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64HsSrv.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64winmm.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64dsound.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64version.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64advapi32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64ole32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64winmmbase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64powrprof.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64sechost.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64rpcrt4.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64combase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64cfgmgr32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64devobj.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64sspicli.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64cryptbase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64bcryptprimitives.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64dwmapi.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64clbcatq.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64oleaut32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:Program Files (x86)DisplayFusionHooksAppHookx86_45641EBC-D115-4D9A-BB79-9CB07566629C.dll'. Module was built without symbols.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64shell32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsWinSxSx86_microsoft.windows.common-controls_6595b64144ccf1df_5.82.9200.16658_none_bf1359a245f1cd12comctl32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:WindowsSysWOW64shlwapi.dll'. Cannot find or open the PDB file.
The program '[9200] Learning C++.exe' has exited with code 3 (0x3).

Answer 1

似乎您希望您的函数在名称数组(names)中找到特定名称(query)。但是这个函数的接口是不正确的。

它的参数names目前是string类型，这意味着它是一个单字符串。如果你想传递全局变量names in，修改函数以接受指向string的指针，并使它指向数组的第一个元素:

string search(int largestNum, int smallestNum, const string *names, string query)
{
  // as before..., except:
  if (query == middleName) return "PresentnLocation:" + std::to_string(middle);
  else return "Not around";
}

在调用点，只传递names而不是names[N](无论如何都是在访问越界索引):

cout << search(largestNum, smallestNum, names, query);

---

原始断言的来源是，用{ "Present", "Location: " + middle }初始化std::string甚至不会做您可能认为它所做的事情。它调用std::string构造函数，该构造函数接受两个迭代器，用于分隔要复制到字符串中的字符范围。

所以你实际上是在告诉程序:"从字面量"Present"的第一个字符的地址开始，一直到字面量"Location: "的第一个字符middle的地址，将中间的所有内容复制到字符串中。"这当然是一团糟。

如果你需要一些学习资源，我们在Stack Overflow上保留了一些优秀的c++书籍列表。

Answer 2

您将names[N]传递给search(..)，但很可能位置100不存在。N设置为100。只需传递一个有效的数组位置或传递整个数组和names的长度来迭代names。此外，您正在使用这一行middleName = names[middle];，但names不是字符串数组，只是string。