我该如何投射一个std :: vector <const unsigned char> 到const std :: vector <unsigned char> ？

Question

How can I cast an std::vector<const unsigned char> to a const std::vector<unsigned char> , without copying the data?

Parser::Parser( const std::vector< unsigned char > &i_Data )
{
    Parse(i_Data);
}

Parser::Parser( std::vector< const unsigned char > i_Data )
{
    Parse( (std::vector< unsigned char >)(i_Data) );  // <-- Error
}

int Parser::Parse( const std::vector< unsigned char > &i_Data )
{ ... }

This is the error message from Visual C++ 2010:

Error C2440 'type cast' : cannot convert from 'std::vector<_Ty>' to 'std::vector<_Ty>'

Answer 1

How can I cast an std::vector<const unsigned char> to a const std::vector<unsigned char> , without copying the data?

You can't. The two types are unrelated.

Instead of having such a strict interface (taking a std::vector< unsigned char > const& ), you should generalize it to take a pair of iterators. In this case, perhaps just two pointers to const unsigned char :

Parser(unsigned char const* begin, unsigned char const* end)
{
    ...
}

Now if you want you can add the two vector constructors to delegate to this one via:

Parser(std::vector<unsigned char> const& v)
: Parser(v.data(), v.data + v.size())
{ }

Note: Pre-C++11, since vector doesn't have a data() function yet, the way to delegate a vector to two pointers be to write something like:

template <class T, class A>
T* data(std::vector<T, A>& v) {
    return v.empty() ? 0 : &v[0];
}

template <class T, class A>
T const* data(std::vector<T, A> const& v) {
    return v.empty() ? 0 : &v[0];
}

And then simply use data(v) instead.

Answer 2

With this cast it compiles correctly:

Parser::Parser( std::vector< const unsigned char > i_Data )
{
    Parse( (std::vector< unsigned char >)(i_Data) );             // <-- Error
    Parse( ( const std::vector< unsigned char > &)( i_Data ) );  // <-- OK
}

int Parser::Parse( const std::vector< unsigned char > &i_Data )
{ ... }