error: declaration of ‘data’ as array of references

Question

C++ application code was compiling fine with GCC 4.1. Now i upgraded the GCC version to 4.4X and i am getting an error.

error: declaration of ‘data’ as array of references

CODE:

  inline std::string base64_encode(const std::vector< unsigned char >& data)
  {
    if (data.empty())
    {
      return "";
    }
    using namespace boost::archive::iterators;
    typedef base64_from_binary<
      transform_width< const unsigned char*, 6, 8> > base64_enc;
    std::string result(base64_enc(&data[0]),
      base64_enc(&data[0] + data.size()));
    static const std::string base64_padding[] = { "", "==", "=" };
    result.append(base64_padding[data.size() % 3]);
    return result;
  }

I read few answers and came to know that this doesn't comply with vexing parse rule.

One possible solution is to enclose (&data)[0] or std::string result({base64_enc(&data[0]}), base64_enc(&data[0] + data.size();

std::string result(base64_enc(&data[0]),
      base64_enc(&data[0] + data.size()));

Compiler should not consider this line as a function declaration. How do i apply the proper grammar in this case ?

What are you trying to accomplish? Do you want to pass an array by reference? — Constantinos Glynos, Mar 25 '19 at 11:38
it simply encodes given sequence of bytes to a base64 string — Deepak Selvakumar, Mar 25 '19 at 11:47

M.M · Answer 1 · 2019-03-25T12:01:55.500

One option is to change std::string result( to std::string result = std::string( (leave the rest of the line the same).

I think it is a compiler bug because &data[0] + data.size() could not occur in a declaration, but I have seen similar bugs in gcc before (it mistakenly flags the line as a declaration too early in parsing).

This version also worked around the bug for me in gcc 8.3, adding an extra set of parentheses:

std::string result ( (base64_enc(&data[0])), base64_enc(&data[0] + data.size()) );
//                   ^                    ^

error: declaration of ‘data’ as array of references

1 Answers1