我的程序在 char* 数组的第 3 个初始化周期中断。 不明白为什么会这样。 请解释

Question

If I try to run program and ititialize only 2 strings (char*), it works OK. But when I try 3, 4 and more strings initialize, then program just stops. What do I miss?

#include <iostream>
#include <cstring>

template <typename T>
T maxn(T*, int);
template <> char* maxn(char**, int);
template <typename T>
void fill_array(T*, int);

int main()
{
    using std::cout;
    using std::cin;
    int N;
    cout << "Input size of array of integers: ";
    cin >> N;
    int *Arr = new int[N];
    fill_array(Arr, N);
    cout << "\nMax number in your array is " << maxn(Arr, N) << '\n';
    delete [] Arr;
    cout << "Input size of array of doubles: ";
    cin >> N;
    double *ArrDouble = new double[N];
    fill_array(ArrDouble, N);
    cout << "\nMax number in your array is " << maxn(ArrDouble, N) << '\n';
    delete [] ArrDouble;
    cout << "Input number of strings, that you plan to input: ";
    cin >> N;
    cin.get();
    char **ArrChar = new char*[N];
    for (int i=0; i<N; i++)
    {
        cout << "Input string #" << i+1 << ": ";
        cin.getline(ArrChar[i], 40);
    }
    cout << "The longest string starts at " << reinterpret_cast<void*>(maxn(ArrChar, N)) << " address";
    delete [] ArrChar;
    return 0;
}

template <typename T>
void fill_array(T* p_T, int N)
{
    for (int i=0; i<N; i++)
    {
        std::cout << "Enter a number #" << i+1 << ": ";
        std::cin >> p_T[i];
    }
    std::cout << "Array was initializated. Well done!\n";
    return;
}

template <typename T>
T maxn(T* p_T, int N)
{
    T max=p_T[0];
    for (int i=0; i<N-1; i++)
    {
        if (p_T[i]<p_T[i+1]) max=p_T[i+1]; 
    }
    return max;
}

template <> char* maxn(char** str, int N)
{
    char* max_len=&str[0][0];
    for (int i=0; i<N-1; i++)
    {
        if (strlen(str[i])<strlen(str[i+1])) max_len=&str[i+1][0];
    }
    return max_len;
}

I suppose, that problem chains with allocate memory, but don't sure. I tried it with fixwd-size array - program breaks after input first string...

Answer 1

Change this

char **ArrChar = new char*[N];
for (int i=0; i<N; i++)
{
    cout << "Input string #" << i+1 << ": ";
    cin.getline(ArrChar[i], 40);
}

to this

char **ArrChar = new char*[N];
for (int i=0; i<N; i++)
{
    ArrChar[i] = new char[40]; // <-- ADD THIS!
    cout << "Input string #" << i+1 << ": ";
    cin.getline(ArrChar[i], 40);
}

You need to allocate some memory for your strings, getline won't do that for you.