Invalid conversion from ‘const char*’ to ‘unsigned char*’ - c++

Question

A simple C++ code:
int main(){
unsigned char* t="123";
}
on compilation with g++ gives following error:
invalid conversion from ‘const char*’ to ‘unsigned char*’ [-fpermissive]
Why?

Answer 1

In C++ string literals have types of constant character arrays. For example string literal "123" has type const char[4].
In expressions with rare exceptions arrays are converted to pointers to their first elements.
So in this declaration
unsigned char* t="123";
the initializer has type const char *. There is no implicit conversion from const char * to unsigned char *
You could write
const unsigned char* t = reinterpret_cast<const unsigned char *>( "123" );

Answer 2

Another approach, which gets you a modifiable unsigned char array as you originally wanted, is:
#include <cstdlib>
#include <iostream>
using std::cout;
using std::endl;
int main()
{
unsigned char ta[] = "123";
unsigned char* t = ta;
cout << t << endl; // Or ta.
return EXIT_SUCCESS;
}
You can add const to both declarations if you wish, to get const unsigned char without an explicit cast.

Answer 3

Simply use
just char* in place of unsigned char* during declaration
char t[MAX_SIZE] = "123"; // MAX_SIZE should be defined earlier
time tested strcpy() and strncpy functions

Answer 4

Conversions from one type to another type is easy when you use self-defined macros. So here is a set of macros you can use across any platform (Windows, Linux, Solaris, AIX etc...)
#define M_ToCharPtr(p) reinterpret_cast<char*>(p) // Cast to char*
#define M_ToWCharPtr(p) reinterpret_cast<wchar_t*>(p) // Cast to wchar_t*
#define M_ToConstCharPtr(p) reinterpret_cast<const char*>(p) // Cast to const char*
#define M_ToConstWCharPtr(p) reinterpret_cast<const wchar_t*>(p) // Cast to const wchar_t*
#define M_ToUCharPtr(p) reinterpret_cast<unsigned char*>(p) // Cast to unsigned char*
#define M_ToConstUCharPtr(p) reinterpret_cast<const unsigned char*>(p) // Cast to const unsigned char*
#define M_ToUCharPtr(n) reinterpret_cast<unsigned char*>(n) // Cast to unsigned char*
#define M_ToVoidPtr(p) reinterpret_cast<void*>(p) // Cast to void*
#define M_ToConstVoidPtr(p) reinterpret_cast<const void*>(p) // Cast to const void*
#define M_ToIntPtr(n) reinterpret_cast<int*>(n) // Cast to int*
#define M_ToConstIntPtr(p) reinterpret_cast<const int*>(p) // Cast to const int*
#define M_ToDoublePtr(n) reinterpret_cast<double*>(n) // Cast to double*
#define M_ToConstDoublePtr(n) reinterpret_cast<const double*>(n) // Cast to const double*
#define M_ToBoolPtr(n) reinterpret_cast<bool*>(n) // Cast to bool*
#define M_ToConstBoolPtr(n) reinterpret_cast<const bool*>(n) // Cast to const bool*
// General Cast
#define M_To(T, p) reinterpret_cast<T>(p) // Cast to T
In your case
const unsigned char* t = reinterpret_cast<const unsigned char *>("UCHAR TO CONST UCHAR");
is equivalent to
const unsigned char* t = M_ToConstUCharPtr("UCHAR TO CONST UCHAR");