C++ reading some bytes at a memory address, output as string - c++

Question

A function returns a pointer and a length (via the arguments) from an unknown DLL.
Result = SpamnEggs( &pBytes, &nBytes )
The pointer points to a valid memory address at which are nBytes sequential bytes.
These bytes contain valid ascci values for text. There is no null termination!
I am tasked with "ovelaying" a string type of some sort in as few simple operations in generic C++ code (without complex libraries or using byte) before output:
cout << sresult
Added:
without copying the bytes as this is a large buffer that must be traversed.
Prototype:
int SpamnEggs( void* pBytes, void* nBytes );
becomes
int SpamnEggs( char** pBytes, int* nBytes );
Many thanks all. Great answers and all very valid.

Answer 1

You can copy the raw memory and add the string terminating character yourself:
char* newStr = new char[size + 1];
memcpy ( newStr, source, size );
newStr[size] = "\0";
cout << newStr;
Without copying memory, you can create a class that holds the pointer and length as members and overload the stream operator to print only length characters:
class MyString
{
void* _pBuf;
int _length;
public:
MyString(void* pBuf, int length)
{
_pBuf = pBuf;
_length = length;
}
friend ostream& operator <<(ostream &os,const MyString& obj);
};
ostream& operator <<(ostream &os,const MyString& obj)
{
const char* pChar = (const char*)obj._pBuf;
for ( int i = 0 ; i < obj._length ; i++ )
{
os << pChar[i];
}
return os;
}
Example usage:
char* x = "blablabla";
int length = 3;
MyString str(x,length);
cout << str;

Answer 2

You can just construct a std::string from the pointer and a length.
std::string sResult(pBytes, nBytes);
std::cout << sResult;
(assuming pBytes is a char* pointer, otherwise you need a small cast).

Answer 3

How about something like this (untested) code:
class my_pointer_string
{
friend std::ostream &operator<<(std::ostream &, const my_pointer_string &);
public:
my_pointer_string(void *ptr, size_t len)
: m_pointer(ptr), m_length(len)
{ }
private:
void *m_pointer;
size_t m_length;
};
std::ostream &operator<<(std::ostream &os, const my_pointer_string &str)
{
char *string = reinterpret_cast<char *>(str.m_pointer);
for (size_t i = 0; i < str.m_length; i++)
os << *string++;
return os;
}

Answer 4

What you would have to do is
a) Create some class that encapsulates the char pointer and the size.
b) Write a << operator for that class to output its content to a stream.
EDIT: In contrast to the response by Bo Persson this would not imply copying the source data.