Question

当我运行这个c ++程序并执行其功能时，我得到了这个内存错误

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

我假设您取消注释代码时会导致错误。让我们来看看错误（你应该是这样做的，使用你的调试器）：

keyString = userInput.substr(locationOfFirstKeyIndex, locationSpace); 
//userInput is a blank string, lOFKI == 0 and so does locationSpace
stoi(keyString); //keyString is invalid, empty string

在解析之前，您应该尝试获取用户输入...

Answer 2

请参阅以下链接以了解此事：

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

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

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

为什么我会出现内存错误？

2 个答案: