String length issues related with strlen()

Just change from sizeof to strlen(), sizeof is evaluated in compile time. sizeof a pointer either gives 4 bytes(32-bit) or 8 bytes(64-bits) and length of your source text is longer than 8 bytes. strlen() is done during runtime. And set the 1st char of pmessage to null character to mean zero length because pmessage is point to a new array with random values. Or you can memset to zero-initialize the whole array. strlen() is checking for null character to determine the string length.

//constructor
CMessage(const char* text = "default message")
{
    if(pmessage) delete [] pmessage; // deallocate pmessage if it is not null, else mem-leak
    pmessage = new char[strlen(text) + 1];
    pmessage[0] = '\0'; // set 1st char to null character to signify 0 length.
    cout << " the length of text is:" << strlen(text) << endl;
    cout << " the length of pmessage is:" << strlen(pmessage) << endl;

    strcpy_s(pmessage,strlen(pmessage)+1,text);
}

I could explain why your C-style coding is not working, but I will just provide a simpler C++ version instead. (this is off the top of my head - I did not compile this, so I expect at least one error)

#include <iostream>
#include <string>
using namespace std;

class CMessage {
private:
    std::string message;

public:
    void ShowIt()
    {
        cout << endl << message.c_str();
    }

    //constructor
    CMessage(const std::string& text = "default message")
    {
        cout << " the length of text is:" << text.size() << endl;
        cout << " the length of message is:" << message.size() << endl;

        message = text;
    }

    //destructor prototype
    ~CMessage();
};

CMessage::~CMessage()
{
    cout << "destructor called."
        << endl;
}



int main()
{
    std::cout << "Hello World!\n";
    CMessage Motto("a miss is as good as a smile.");
    Motto.ShowIt();
}

Take note that if you are using the keyword 'new' in C++, then you are probably doing something wrong. There are valid reasons for using pointers and allocating memory with 'new' in C++, but your simple program is not one of them.

There are reasons why you might want to pass a constant c-string pointer to methods in C++, but I leave that up to you to figure out.

std::string together with std::cout provide (correctly) all the functionality your code should.
Hence, in order to brush your C++ skills, give a look at their documentation.