执行程序时出错：“进程返回 -1073741819 (0xC0000005)”

为什么程序S_object.findShortestWord(S_object.get(), str_value2);以终止Process returned -1073741819 (0xC0000005) execution time : 3.804 s？

#include <iostream>
#include <stdio.h>
#include <cstring>

using namespace std;

class FirstClass {
    public:
        char* str_value;
    public:
        FirstClass(const char* value = ""):str_value(0) {
            set(value);
        }

        FirstClass(const FirstClass &obj):str_value(0) {
            set(obj.str_value);
        };

        ~FirstClass() {delete[] str_value;}

    void set(const char* value) {
        delete[] str_value;
        str_value = new char[strlen(value)+1];
        strcpy(str_value, value);
    }

    const char* get() const {
        return str_value;
    }
};

class SecondClass : public FirstClass {
    public:
        SecondClass(const char* str_value = "") : FirstClass (str_value) {}
    void findShortestWord(const char* in, char* out) {
        int len = strlen(in);

        int beginWord = 0;
        int lengthWord = 0;

        for (int i = 0; i < len; i++) {
            while ( (in[i] == ' ') && ( in[i] != '\0')  ) i++;
            int begin = i;
            while ( (in[i] != ' ') && (in[i] != '\0') ) i++;
            int end = i;
            char tmp[256];
            for(int j = begin, k=0; j < end; j++, k++)
                tmp[k] = in[j];
            tmp[end - begin] = '\0';

            int currentLen = end - begin;
            if (currentLen < lengthWord) {
                lengthWord = currentLen;
                beginWord = begin;
            }
}

        for (int i = beginWord, k = 0; i < beginWord + lengthWord; i++, k++)
            out[k] = in[i];

        out[lengthWord] = '\0';
    }
};

int main() {
    char* str_value2;
    FirstClass F_object("Hello my world 1");

    printf("\nFirstClass init: %s", F_object.get());

    F_object.set("Hello my world 2");

    printf("\nFirstClass set: %s", F_object.get());

    FirstClass F_object2 = F_object;

    SecondClass S_object(F_object.get());

    printf("\nSecondClass init: %s", S_object.get());

    S_object.findShortestWord(S_object.get(), str_value2);

    //F_object = S_object;

    printf("\nSearch and delete: %s", str_value2);

    return 0;
}