How to write an analogue of the strcpy() function with memory allocation?

Question

C++ / C#

According to the task, you need to write a function, copying a string, into a new string with memory allocation. Why should it be allocated in this function?
Unfortunately, according to the code, nothing comes to mind. Google also gives inappropriate options.
This ... works, but to me, it's an unfortunate option.

char *str1 = "123456789112345";
    char *str2 = "sdf";
    str1 = str2;
    cout << str1 << endl;
    cout << str2 << endl;

Answer 1

you need to write a function, copying a string, to a new string with memory allocation

This is the POSIX strdup() function.
You can see how it works.
Something like this:

char* strdup( const char *s ) {
   char *p = malloc( strlen( s ) + 1 );
   if( p ) strcpy( p, s );
   return p;
}

Answer 2

If you are using iostreams, work with std::string. If a teacher is interfering with C and C++ in front of the students, tell him he's weird.