Question

我正在尝试学习编码，并正在创建一个二进制搜索程序。当我尝试运行我的代码时，当我尝试调用搜索功能时，我得到调试断言失败（请参阅下面的调试输出）。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" };
}

DEBUG OUTPUT

'Learning C++.exe' (Win32): Loaded 'C:\Users\Gareth\Programming\Projects\Learning C++\Debug\Learning C++.exe'. Symbols loaded.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\ntdll.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\kernel32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\KernelBase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\msvcp120d.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\msvcr120d.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\user32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\gdi32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\imm32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\msctf.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\msvcrt.dll'. Cannot find or open the PDB file.
Debug Assertion Failed!

Program: C:\Windows\SYSTEM32\MSVCP120D.dll
File: c:\program files (x86)\microsoft visual studio 12.0\vc\include\xstring
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:\Windows\SysWOW64\uxtheme.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\HsSrv.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\winmm.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\dsound.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\version.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\advapi32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\ole32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\winmmbase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\powrprof.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\sechost.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\rpcrt4.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\combase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\cfgmgr32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\devobj.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\sspicli.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\cryptbase.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\bcryptprimitives.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\dwmapi.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\clbcatq.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\oleaut32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Program Files (x86)\DisplayFusion\Hooks\AppHookx86_45641EBC-D115-4D9A-BB79-9CB07566629C.dll'. Module was built without symbols.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\shell32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\WinSxS\x86_microsoft.windows.common-controls_6595b64144ccf1df_5.82.9200.16658_none_bf1359a245f1cd12\comctl32.dll'. Cannot find or open the PDB file.
'Learning C++.exe' (Win32): Loaded 'C:\Windows\SysWOW64\shlwapi.dll'. Cannot find or open the PDB file.
The program '[9200] Learning C++.exe' has exited with code 3 (0x3).

Answer 1

您似乎希望您的函数在您的名称数组（query）中找到特定名称（names）。但是函数的界面不正确。

其参数names目前的类型为string，这意味着它是单个字符串。如果要传递全局变量names在，更改函数以接受指向string的指针，并使其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 "Present\nLocation:" + std::to_string(middle);
  else return "Not around";
}

在呼叫网站上，只需传递names而不是names[N]（无论如何都是访问越界索引）：

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

原始断言的来源是用std::string初始化{ "Present", "Location: " + middle }并不能远远超出您的想象。它调用带有两个迭代器的std::string构造函数，期望分隔一系列字符以复制到字符串中。

所以你有效地告诉了程序：＆＃34;从文字"Present"中第一个字符的地址开始，然后继续，直到到达middle个字符的地址文字"Location: "，将其中的所有内容复制到字符串中。这当然是一个绝对的混乱。

如果您需要一些学习资源，我们会在Stack Overflow上保留list of good C++ books。

Answer 2

您正在将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，并传递names的长度以迭代names。您也使用此行middleName = names[middle];，但names不是字符串数组，只是string。

Debug Assertion Failure：字符串下标超出范围

2 个答案: