c++ - 为什么我会收到内存错误？

Question

当我运行这个 C++ 程序并执行它的函数时，我得到了这个内存错误，不知道为什么

TESTER 12345.exe 中 0x769DC41F 处的未处理异常:Microsoft C++ 异常:内存位置 0x0042F558 处的 std::invalid_argument。

我在 Visual Studio 2013 上运行它。

#include <iostream>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cmath>

using namespace std;

string encrypt(string, int);
string decrypt(string source, int key);
int main(int argc, char *argv[])
{
    string Source;
    string userInput;
    string keyString;

    int Key;
    int locationSpace = 0;
    int locationOfFirstKeyIndex = 0;

    int choice;

    /*locationSpace = userInput.find(" ");

    keyString = userInput.substr(locationOfFirstKeyIndex, locationSpace);
    Source = userInput.substr(locationSpace + 1);

    Key = stoi(keyString);*/

    cout << "To encode a message type 1, to decode a message type 2: ";
    cin >> choice;

    if (choice == 1)
    {
        cin.ignore();
        cout << "Enter a message to decode: ";
        getline(cin, Source);
        locationSpace = userInput.find(" ");

        keyString = userInput.substr(locationOfFirstKeyIndex, locationSpace);
        Key = stoi(keyString);
        Source = userInput.substr(locationSpace + 1);

        encrypt(Source, Key);
        cout << "Encrypted: " << encrypt(Source, Key) << endl;
    }
    else if (choice == 2)
    {
        cin.ignore();
        cout << "Enter the message To decode: ";
        getline(cin, userInput);
        locationSpace = userInput.find(" ");

        keyString = userInput.substr(locationOfFirstKeyIndex, locationSpace);
        Key = stoi(keyString);
        Source = userInput.substr(locationSpace + 1);


        decrypt(Source, Key);
        cout << "Decrypted: " << decrypt(Source, Key) << endl;
    }
    else
    {

        cout << "Invalid Input";
    }

    system("pause");
}

string encrypt(string source, int key)
{
    string Crypted = source;

    for (int Current = 0; Current < source.length(); Current++)
        Crypted[Current] = ((Crypted[Current] + key) - 32) % 95 + 32;
    return Crypted;
}

string decrypt(string source, int key)
{
    string Crypted = source;

    for (int Current = 0; Current < source.length(); Current++)
        Crypted[Current] = ((Crypted[Current] - key) - 32 + 3 * 95) % 95 + 32;
    return Crypted;
}

Answer 1

请引用以下链接了解这一点:

http://en.cppreference.com/w/cpp/string/basic_string/stol

stoi 方法在无法执行任何转换时抛出 *std::invalid_argument* 异常。您可能希望在将其传递给 stoi() 之前进行打印，并验证字符串是否有效。

std::cout<<keyString<<std::endl;