问C++：为什么这段代码会给我内存问题/未定义的行为？

EN

#include <iostream>


using namespace std;

unsigned short pec15Table[256];
const unsigned int CRC15_POLY = 0x4599;



void init_PEC15_Table() // Cyclical Redundancy Check lookup table generator function
{
    unsigned short rem;
    for (int i = 0; i < 256; i++)
    {
        rem = i << 7;
        for (int bit = 8; bit > 0; --bit)
        {
            if (rem & 0x4000)
            {
                rem = ((rem << 1));
                rem = (rem ^ CRC15_POLY);
            }
            else
            {
                rem = ((rem << 1));
            }
        }
        pec15Table[i] = rem & 0xFFFF;
//        cout << hex << pec15Table [i] << endl;
    }
}

 unsigned short pec15(char* data, int lengt = 16)  //Takes data as an input,
{
     int rem, address;
     rem = 16;//PEC seed (intial PEC value)
    for (int i = 0; i < lengt; i++)
    {
        address = ((rem >> 7) ^ data[i]) & 0xff;//calculate PEC table address
        rem = (rem << 8) ^ pec15Table[address];
    }
    return (rem * 2);//The CRC15 has a 0 in the LSB so the final value must be multiplied by 2
}

int main()
{
    init_PEC15_Table();         //initialise pec table
    char data = (short) 0x1 ;   // Write 0x1 to char array containing the data 0x1
    char* dataPtr = &data;      // Create a pointer to that array

    unsigned short result = pec15(dataPtr);                    //Pass data pointer to pec calculator


    cout << "data in: " << (short) *dataPtr << endl;        //Print the short representation of the char data array (Outputs 1)
    cout << "size of data: " << sizeof(*dataPtr) << endl;   //Print the size of the char array (Outputs 1)
    cout << "stuffed pec: " << result << endl;                 //Print the output of the pec calculation    

    return 0;
}