c++: implement write_padding function

Question

The following question had been asked probably, but I couldn't find it.

I have create a class BinaryWriter.
I need to implement the following method:

  /// Write zero bytes to file
  virtual void wr_padding( int padding_size);

I have the following implementation:

void BinaryWriter::wr_padding( int padding_size)
{
  char pad_arr[padding_size];
  memset(pad_arr, 0, padding_size);
  m_stream.write(pad_arr,padding_size);
}

where:

   std::ostream m_stream;

I'm not to happy with this implementation. I was hoping to have an ios API for this simple task. Is there more native implementation?

Thanks

@DannyElly The dimensions of a C style array must be a constant. — James Kanze, Nov 04 '13 at 09:57
that is correct. but oddly enough, this code compiles and operational. — idanshmu, Nov 04 '13 at 10:00
You're comment `Write zero bytes...` might easily be misunderstood. — Zane, Nov 04 '13 at 10:01
@DannyElly That's because your compiler has a non-standard language extension — jrok, Nov 04 '13 at 10:01
Take a look at this answer (How to write 'n' copies of a character to ostream) : http://stackoverflow.com/a/11421715/808101 — benjarobin, Nov 04 '13 at 09:56

score 2 · Accepted Answer · answered Nov 04 '13 at 09:56

2

First, your code isn't valid; the size of a C style array must be a constant. A valid version would be:

void
BinaryWriter::wr_padding( int padding_size)
{
  std::vector<char> pad_arr( padding_size );
  m_stream.write( &pad_arr[0], pad_arr.size() );
}

However: can you set some maximum value for padding_size? (In XDR, for example, it will never be more than 4.) If so, something as simple as:

void
BinaryWriter::wr_padding( int padding_size )
{
    static char const pad_arr[ max_padding_size ] = {};
    m_stream.write( pad_arr, padding_size );
}

would do the trick.

answered Nov 04 '13 at 09:56

James Kanze

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This is valid C++, if you are not using a old compiler... In C you can do that in c99 – benjarobin Nov 04 '13 at 09:58
@benjarobin c99 != C++. It's not valid C++, period. – jrok Nov 04 '13 at 10:00
@benjarobin It is valid C99, but it is _not_ valid C++. – James Kanze Nov 04 '13 at 10:57
@jrok You were right, gcc/g++ allow it if -pedantic is not specified: my bad – benjarobin Nov 04 '13 at 12:43

c++: implement write_padding function

1 Answers1