Re: How to encode text into html format

James Kanze <>
Mon, 2 Jun 2008 01:17:08 -0700 (PDT)
On Jun 1, 11:01 pm, Kai-Uwe Bux <> wrote:

James Kanze wrote:

On Jun 1, 8:11 pm, Kai-Uwe Bux <> wrote:

Fred Yu wrote:

I want to encode input text into html format such as
replace "<" with "&lt", replace "&" with "&amp". Could
you give me some ideas? Thanks.

Containers: std::map< char, std::string >
Iterators: std::istream_iterator, std::ostream_iterator
Algorithms: std::transform

Agreed for the first (although it may be overkill---in this
particular case, I think I'd go with a simple switch).

No real need for the second; just use istream::get() and
ostream::put() (or operator<< in some cases).

As to the third: how? You're replacing a single character
with a sequence of characters, and transform does a one to
one (which in practice makes it of fairly limited
utility---although I've used it with a vector<string>,
ostream_iterator, and as string transformer class that I've
written, which works something like $(patsubst...) in GNU

I was thinking of something like this:

#include <iostream>
#include <iterator>
#include <map>
#include <algorithm>
#include <cassert>

struct encoder {

  std::map< char, std::string > the_map;

  encoder ( void ) {
    the_map[ 'a' ] = "a";
    // ...
    the_map[ '&' ] = "&amp";
    // ...

  std::string const & operator() ( char ch ) const {
    std::map< char, std::string >::const_iterator iter =
      the_map.find( ch );
    assert( iter != the_map.end() );
    return ( iter->second );

int main ( void ) {
  encoder the_encoder;
  std::transform( std::istreambuf_iterator<char>( std::cin ),
                  std::ostream_iterator<std::string>( std::cout, "" ),
                  the_encoder );

Which looks like a lot of overhead (including in terms of
programming) for very little gain. It might be worth it if you
create some sort of generic encoder, in order to reuse the idiom
in many different contexts, but for such a simple problem, it
just seems overkill for a onetime solution. As I said, I'd
probably go with the switch. If I were going to go to the
effort of initializing the map completely, I'd probably go with
a char const*[UCHAR_MAX], rather than std::map. Or a map with
just the elements which don't use an identity transformation.
And I'd probably still write out the loop; somehow, the idea of
transforming each individual character into a string just to
output it bothers me.

James Kanze (GABI Software)
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