Re: std::string in C-style in interface

From:

SG <s.gesemann@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 10 Sep 2010 02:20:25 -0700 (PDT)

Message-ID:

<b6d73f1a-50ae-4f66-9284-8749fa5c66b1@z25g2000vbn.googlegroups.com>

On 10 Sep., 10:36, James Kanze wrote:

On Sep 9, 11:49 pm, Seungbeom Kim wrote:

On 2010-09-08 23:53, Kai Wen wrote:

On 2010-09-09, SG wrote:

  vector<char> temp;
  temp.reserve(thestring.size()+1);
  temp.assign(thestring.begin(),thestring.end());
  temp.push_back('\0');
  foo(&temp[0]);
  thestring = &temp[0];

But I think this method is too complex. :-(

Maybe the four lines before calling foo can be shortened to two:
const char *b = thestring.c_str(), *e = b + thestring.size(=

) + 1;

vector<char> temp(b, e);

Nice.

Or even to:
std::vector<char> temp(thestring.begin(), thestring.end()=

);

foo probably expects a null-terimated string.

Similarly, the last line could just as easily be:
thestring.assign(temp.begin(), temp.end());

I intentionally used

thestring = &temp[0];

in case foo tries to shorten the string.

The best solution depends on context, however. If the legacy
function is actually returning a string value in the buffer (and
doesn't use the initial contents), something like the following
may be appropriate:

     std::string
     getCurrentWorkingDirectory()
     {
         std::vector<char> results( 1000 );
         errno = 0;
         while ( getcwd(&results[0], results.size() ) == NULL
                 && errno == ERANGE) {
             results.resize( 2 * results.size() );
             errno = 0;
         }
         if ( errno != 0 )
             throw SomeError();
         return std::string( results.begin(), results.end() );
     }

Are you sure that you don't want

return std::string(&results[0]);

here?

Cheers!
SG