src/common/stringimpl.cpp

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        src/common/stringimpl.cpp
   3 // Purpose:     wxString class
   4 // Author:      Vadim Zeitlin, Ryan Norton
   5 // Modified by:
   6 // Created:     29/01/98
   7 // RCS-ID:      $Id$
   8 // Copyright:   (c) 1998 Vadim Zeitlin <zeitlin@dptmaths.ens-cachan.fr>
   9 //              (c) 2004 Ryan Norton <wxprojects@comcast.net>
  10 // Licence:     wxWindows licence
  11 /////////////////////////////////////////////////////////////////////////////
  12
  13 /*
  14  * About ref counting:
  15  *  1) all empty strings use g_strEmpty, nRefs = -1 (set in Init())
  16  *  2) AllocBuffer() sets nRefs to 1, Lock() increments it by one
  17  *  3) Unlock() decrements nRefs and frees memory if it goes to 0
  18  */
  19
  20 // ===========================================================================
  21 // headers, declarations, constants
  22 // ===========================================================================
  23
  24 // For compilers that support precompilation, includes "wx.h".
  25 #include "wx/wxprec.h"
  26
  27 #ifdef __BORLANDC__
  28     #pragma hdrstop
  29 #endif
  30
  31 #ifndef WX_PRECOMP
  32     #include "wx/stringimpl.h"
  33     #include "wx/wxcrt.h"
  34 #endif
  35
  36 #include <ctype.h>
  37
  38 #ifndef __WXWINCE__
  39     #include <errno.h>
  40 #endif
  41
  42 #include <string.h>
  43 #include <stdlib.h>
  44
  45 // allocating extra space for each string consumes more memory but speeds up
  46 // the concatenation operations (nLen is the current string's length)
  47 // NB: EXTRA_ALLOC must be >= 0!
  48 #define EXTRA_ALLOC       (19 - nLen % 16)
  49
  50
  51 // string handling functions used by wxString:
  52 #if wxUSE_UNICODE_UTF8
  53     #define wxStringMemcpy   memcpy
  54     #define wxStringMemcmp   memcmp
  55     #define wxStringMemchr   memchr
  56 #else
  57     #define wxStringMemcpy   wxTmemcpy
  58     #define wxStringMemcmp   wxTmemcmp
  59     #define wxStringMemchr   wxTmemchr
  60 #endif
  61
  62
  63 // ---------------------------------------------------------------------------
  64 // static class variables definition
  65 // ---------------------------------------------------------------------------
  66
  67 #if !wxUSE_STL_BASED_WXSTRING
  68 //According to STL _must_ be a -1 size_t
  69 const size_t wxStringImpl::npos = (size_t) -1;
  70 #endif
  71
  72 // ----------------------------------------------------------------------------
  73 // static data
  74 // ----------------------------------------------------------------------------
  75
  76 #if wxUSE_STL_BASED_WXSTRING
  77
  78 // FIXME-UTF8: get rid of this, have only one wxEmptyString
  79 #if wxUSE_UNICODE_UTF8
  80 const wxStringCharType WXDLLIMPEXP_BASE *wxEmptyStringImpl = "";
  81 #endif
  82 const wxChar WXDLLIMPEXP_BASE *wxEmptyString = wxT("");
  83
  84 #else
  85
  86 // for an empty string, GetStringData() will return this address: this
  87 // structure has the same layout as wxStringData and it's data() method will
  88 // return the empty string (dummy pointer)
  89 static const struct
  90 {
  91   wxStringData data;
  92   wxStringCharType dummy;
  93 } g_strEmpty = { {-1, 0, 0}, wxT('\0') };
  94
  95 // empty C style string: points to 'string data' byte of g_strEmpty
  96 #if wxUSE_UNICODE_UTF8
  97 // FIXME-UTF8: get rid of this, have only one wxEmptyString
  98 const wxStringCharType WXDLLIMPEXP_BASE *wxEmptyStringImpl = &g_strEmpty.dummy;
  99 const wxChar WXDLLIMPEXP_BASE *wxEmptyString = wxT("");
 100 #else
 101 const wxStringCharType WXDLLIMPEXP_BASE *wxEmptyString = &g_strEmpty.dummy;
 102 #endif
 103
 104 #endif
 105
 106
 107 #if !wxUSE_STL_BASED_WXSTRING
 108
 109 // ----------------------------------------------------------------------------
 110 // private classes
 111 // ----------------------------------------------------------------------------
 112
 113 // this small class is used to gather statistics for performance tuning
 114
 115 // uncomment this to enable gathering of some statistics about wxString
 116 // efficiency
 117 //#define WXSTRING_STATISTICS
 118
 119 #ifdef  WXSTRING_STATISTICS
 120   class Averager
 121   {
 122   public:
 123     Averager(const wxStringCharType *sz) { m_sz = sz; m_nTotal = m_nCount = 0; }
 124    ~Averager()
 125     {
 126         wxPrintf("wxString %s: total = %lu, average = %f\n",
 127                  m_sz, m_nTotal, ((float)m_nTotal)/m_nCount);
 128     }
 129
 130     void Add(size_t n) { m_nTotal += n; m_nCount++; }
 131
 132   private:
 133     unsigned long m_nCount, m_nTotal;
 134     const wxStringCharType *m_sz;
 135   } g_averageLength("allocation size"),
 136     g_averageSummandLength("summand length"),
 137     g_averageConcatHit("hit probability in concat"),
 138     g_averageInitialLength("initial string length");
 139
 140   #define STATISTICS_ADD(av, val) g_average##av.Add(val)
 141 #else
 142   #define STATISTICS_ADD(av, val)
 143 #endif // WXSTRING_STATISTICS
 144
 145 // ===========================================================================
 146 // wxStringData class deallocation
 147 // ===========================================================================
 148
 149 #if defined(__VISUALC__) && defined(_MT) && !defined(_DLL)
 150 #  pragma message (__FILE__ ": building with Multithreaded non DLL runtime has a performance impact on wxString!")
 151 void wxStringData::Free()
 152 {
 153     free(this);
 154 }
 155 #endif
 156
 157 // ===========================================================================
 158 // wxStringImpl
 159 // ===========================================================================
 160
 161 // takes nLength elements of psz starting at nPos
 162 void wxStringImpl::InitWith(const wxStringCharType *psz,
 163                             size_t nPos, size_t nLength)
 164 {
 165   Init();
 166
 167   // if the length is not given, assume the string to be NUL terminated
 168   if ( nLength == npos ) {
 169     wxASSERT_MSG( nPos <= wxStrlen(psz), wxT("index out of bounds") );
 170
 171     nLength = wxStrlen(psz + nPos);
 172   }
 173
 174   STATISTICS_ADD(InitialLength, nLength);
 175
 176   if ( nLength > 0 ) {
 177     // trailing '\0' is written in AllocBuffer()
 178     if ( !AllocBuffer(nLength) ) {
 179       wxFAIL_MSG( wxT("out of memory in wxStringImpl::InitWith") );
 180       return;
 181     }
 182     wxStringMemcpy(m_pchData, psz + nPos, nLength);
 183   }
 184 }
 185
 186 wxStringImpl::wxStringImpl(const_iterator first, const_iterator last)
 187 {
 188   if ( last >= first )
 189   {
 190     InitWith(first.GetPtr(), 0, last - first);
 191   }
 192   else
 193   {
 194     wxFAIL_MSG( wxT("first must be before last") );
 195     Init();
 196   }
 197 }
 198
 199 wxStringImpl::wxStringImpl(size_type n, wxStringCharType ch)
 200 {
 201   Init();
 202   append(n, ch);
 203 }
 204
 205 // ---------------------------------------------------------------------------
 206 // memory allocation
 207 // ---------------------------------------------------------------------------
 208
 209 // allocates memory needed to store a C string of length nLen
 210 bool wxStringImpl::AllocBuffer(size_t nLen)
 211 {
 212   // allocating 0 sized buffer doesn't make sense, all empty strings should
 213   // reuse g_strEmpty
 214   wxASSERT( nLen >  0 );
 215
 216   // make sure that we don't overflow
 217   wxCHECK( nLen < (INT_MAX / sizeof(wxStringCharType)) -
 218                   (sizeof(wxStringData) + EXTRA_ALLOC + 1), false );
 219
 220   STATISTICS_ADD(Length, nLen);
 221
 222   // allocate memory:
 223   // 1) one extra character for '\0' termination
 224   // 2) sizeof(wxStringData) for housekeeping info
 225   wxStringData* pData = (wxStringData*)
 226     malloc(sizeof(wxStringData) + (nLen + EXTRA_ALLOC + 1)*sizeof(wxStringCharType));
 227
 228   if ( pData == NULL ) {
 229     // allocation failures are handled by the caller
 230     return false;
 231   }
 232
 233   pData->nRefs        = 1;
 234   pData->nDataLength  = nLen;
 235   pData->nAllocLength = nLen + EXTRA_ALLOC;
 236   m_pchData           = pData->data();  // data starts after wxStringData
 237   m_pchData[nLen]     = wxT('\0');
 238   return true;
 239 }
 240
 241 // must be called before changing this string
 242 bool wxStringImpl::CopyBeforeWrite()
 243 {
 244   wxStringData* pData = GetStringData();
 245
 246   if ( pData->IsShared() ) {
 247     pData->Unlock();                // memory not freed because shared
 248     size_t nLen = pData->nDataLength;
 249     if ( !AllocBuffer(nLen) ) {
 250       // allocation failures are handled by the caller
 251       return false;
 252     }
 253     wxStringMemcpy(m_pchData, pData->data(), nLen);
 254   }
 255
 256   wxASSERT( !GetStringData()->IsShared() );  // we must be the only owner
 257
 258   return true;
 259 }
 260
 261 // must be called before replacing contents of this string
 262 bool wxStringImpl::AllocBeforeWrite(size_t nLen)
 263 {
 264   wxASSERT( nLen != 0 );  // doesn't make any sense
 265
 266   // must not share string and must have enough space
 267   wxStringData* pData = GetStringData();
 268   if ( pData->IsShared() || pData->IsEmpty() ) {
 269     // can't work with old buffer, get new one
 270     pData->Unlock();
 271     if ( !AllocBuffer(nLen) ) {
 272       // allocation failures are handled by the caller
 273       return false;
 274     }
 275   }
 276   else {
 277     if ( nLen > pData->nAllocLength ) {
 278       // realloc the buffer instead of calling malloc() again, this is more
 279       // efficient
 280       STATISTICS_ADD(Length, nLen);
 281
 282       nLen += EXTRA_ALLOC;
 283
 284       pData = (wxStringData*)
 285           realloc(pData,
 286                   sizeof(wxStringData) + (nLen + 1)*sizeof(wxStringCharType));
 287
 288       if ( pData == NULL ) {
 289         // allocation failures are handled by the caller
 290         // keep previous data since reallocation failed
 291         return false;
 292       }
 293
 294       pData->nAllocLength = nLen;
 295       m_pchData = pData->data();
 296     }
 297   }
 298
 299   wxASSERT( !GetStringData()->IsShared() );  // we must be the only owner
 300
 301   // it doesn't really matter what the string length is as it's going to be
 302   // overwritten later but, for extra safety, set it to 0 for now as we may
 303   // have some junk in m_pchData
 304   GetStringData()->nDataLength = 0;
 305
 306   return true;
 307 }
 308
 309 wxStringImpl& wxStringImpl::append(size_t n, wxStringCharType ch)
 310 {
 311     size_type len = length();
 312
 313     if ( !Alloc(len + n) || !CopyBeforeWrite() ) {
 314       wxFAIL_MSG( wxT("out of memory in wxStringImpl::append") );
 315       return *this;
 316     }
 317     GetStringData()->nDataLength = len + n;
 318     m_pchData[len + n] = '\0';
 319     for ( size_t i = 0; i < n; ++i )
 320         m_pchData[len + i] = ch;
 321     return *this;
 322 }
 323
 324 void wxStringImpl::resize(size_t nSize, wxStringCharType ch)
 325 {
 326     size_t len = length();
 327
 328     if ( nSize < len )
 329     {
 330         erase(begin() + nSize, end());
 331     }
 332     else if ( nSize > len )
 333     {
 334         append(nSize - len, ch);
 335     }
 336     //else: we have exactly the specified length, nothing to do
 337 }
 338
 339 // allocate enough memory for nLen characters
 340 bool wxStringImpl::Alloc(size_t nLen)
 341 {
 342   wxStringData *pData = GetStringData();
 343   if ( pData->nAllocLength <= nLen ) {
 344     if ( pData->IsEmpty() ) {
 345       STATISTICS_ADD(Length, nLen);
 346
 347       nLen += EXTRA_ALLOC;
 348
 349       pData = (wxStringData *)
 350              malloc(sizeof(wxStringData) + (nLen + 1)*sizeof(wxStringCharType));
 351
 352       if ( pData == NULL ) {
 353         // allocation failure handled by caller
 354         return false;
 355       }
 356
 357       pData->nRefs = 1;
 358       pData->nDataLength = 0;
 359       pData->nAllocLength = nLen;
 360       m_pchData = pData->data();  // data starts after wxStringData
 361       m_pchData[0u] = wxT('\0');
 362     }
 363     else if ( pData->IsShared() ) {
 364       pData->Unlock();                // memory not freed because shared
 365       size_t nOldLen = pData->nDataLength;
 366       if ( !AllocBuffer(nLen) ) {
 367         // allocation failure handled by caller
 368         return false;
 369       }
 370       // +1 to copy the terminator, too
 371       memcpy(m_pchData, pData->data(), (nOldLen+1)*sizeof(wxStringCharType));
 372       GetStringData()->nDataLength = nOldLen;
 373     }
 374     else {
 375       nLen += EXTRA_ALLOC;
 376
 377       pData = (wxStringData *)
 378         realloc(pData, sizeof(wxStringData) + (nLen + 1)*sizeof(wxStringCharType));
 379
 380       if ( pData == NULL ) {
 381         // allocation failure handled by caller
 382         // keep previous data since reallocation failed
 383         return false;
 384       }
 385
 386       // it's not important if the pointer changed or not (the check for this
 387       // is not faster than assigning to m_pchData in all cases)
 388       pData->nAllocLength = nLen;
 389       m_pchData = pData->data();
 390     }
 391   }
 392   //else: we've already got enough
 393   return true;
 394 }
 395
 396 wxStringImpl::iterator wxStringImpl::begin()
 397 {
 398     if ( !empty() )
 399         CopyBeforeWrite();
 400     return m_pchData;
 401 }
 402
 403 wxStringImpl::iterator wxStringImpl::end()
 404 {
 405     if ( !empty() )
 406         CopyBeforeWrite();
 407     return m_pchData + length();
 408 }
 409
 410 wxStringImpl::iterator wxStringImpl::erase(iterator it)
 411 {
 412     size_type idx = it - begin();
 413     erase(idx, 1);
 414     return begin() + idx;
 415 }
 416
 417 wxStringImpl& wxStringImpl::erase(size_t nStart, size_t nLen)
 418 {
 419     wxASSERT(nStart <= length());
 420     size_t strLen = length() - nStart;
 421     // delete nLen or up to the end of the string characters
 422     nLen = strLen < nLen ? strLen : nLen;
 423     wxStringImpl strTmp(c_str(), nStart);
 424     strTmp.append(c_str() + nStart + nLen, length() - nStart - nLen);
 425
 426     swap(strTmp);
 427     return *this;
 428 }
 429
 430 wxStringImpl& wxStringImpl::insert(size_t nPos,
 431                                    const wxStringCharType *sz, size_t n)
 432 {
 433     wxASSERT( nPos <= length() );
 434
 435     if ( n == npos ) n = wxStrlen(sz);
 436     if ( n == 0 ) return *this;
 437
 438     if ( !Alloc(length() + n) || !CopyBeforeWrite() ) {
 439         wxFAIL_MSG( wxT("out of memory in wxStringImpl::insert") );
 440         return *this;
 441     }
 442
 443     memmove(m_pchData + nPos + n, m_pchData + nPos,
 444             (length() - nPos) * sizeof(wxStringCharType));
 445     memcpy(m_pchData + nPos, sz, n * sizeof(wxStringCharType));
 446     GetStringData()->nDataLength = length() + n;
 447     m_pchData[length()] = '\0';
 448
 449     return *this;
 450 }
 451
 452 void wxStringImpl::swap(wxStringImpl& str)
 453 {
 454     wxStringCharType* tmp = str.m_pchData;
 455     str.m_pchData = m_pchData;
 456     m_pchData = tmp;
 457 }
 458
 459 size_t wxStringImpl::find(const wxStringImpl& str, size_t nStart) const
 460 {
 461     // deal with the special case of empty string first
 462     const size_t nLen = length();
 463     const size_t nLenOther = str.length();
 464
 465     if ( !nLenOther )
 466     {
 467         // empty string is a substring of anything
 468         return 0;
 469     }
 470
 471     if ( !nLen )
 472     {
 473         // the other string is non empty so can't be our substring
 474         return npos;
 475     }
 476
 477     wxASSERT( str.GetStringData()->IsValid() );
 478     wxASSERT( nStart <= nLen );
 479
 480     const wxStringCharType * const other = str.c_str();
 481
 482     // anchor
 483     const wxStringCharType* p =
 484         (const wxStringCharType*)wxStringMemchr(c_str() + nStart,
 485                                                 *other,
 486                                                 nLen - nStart);
 487
 488     if ( !p )
 489         return npos;
 490
 491     while ( p - c_str() + nLenOther <= nLen &&
 492             wxStringMemcmp(p, other, nLenOther) )
 493     {
 494         p++;
 495
 496         // anchor again
 497         p = (const wxStringCharType*)
 498                 wxStringMemchr(p, *other, nLen - (p - c_str()));
 499
 500         if ( !p )
 501             return npos;
 502     }
 503
 504     return p - c_str() + nLenOther <= nLen ? p - c_str() : npos;
 505 }
 506
 507 size_t wxStringImpl::find(const wxStringCharType* sz,
 508                           size_t nStart, size_t n) const
 509 {
 510     return find(wxStringImpl(sz, n), nStart);
 511 }
 512
 513 size_t wxStringImpl::find(wxStringCharType ch, size_t nStart) const
 514 {
 515     wxASSERT( nStart <= length() );
 516
 517     const wxStringCharType *p = (const wxStringCharType*)
 518         wxStringMemchr(c_str() + nStart, ch, length() - nStart);
 519
 520     return p == NULL ? npos : p - c_str();
 521 }
 522
 523 size_t wxStringImpl::rfind(const wxStringImpl& str, size_t nStart) const
 524 {
 525     wxASSERT( str.GetStringData()->IsValid() );
 526     wxASSERT( nStart == npos || nStart <= length() );
 527
 528     if ( length() >= str.length() )
 529     {
 530         // avoids a corner case later
 531         if ( empty() && str.empty() )
 532             return 0;
 533
 534         // "top" is the point where search starts from
 535         size_t top = length() - str.length();
 536
 537         if ( nStart == npos )
 538             nStart = length() - 1;
 539         if ( nStart < top )
 540             top = nStart;
 541
 542         const wxStringCharType *cursor = c_str() + top;
 543         do
 544         {
 545             if ( wxStringMemcmp(cursor, str.c_str(), str.length()) == 0 )
 546             {
 547                 return cursor - c_str();
 548             }
 549         } while ( cursor-- > c_str() );
 550     }
 551
 552     return npos;
 553 }
 554
 555 size_t wxStringImpl::rfind(const wxStringCharType* sz,
 556                            size_t nStart, size_t n) const
 557 {
 558     return rfind(wxStringImpl(sz, n), nStart);
 559 }
 560
 561 size_t wxStringImpl::rfind(wxStringCharType ch, size_t nStart) const
 562 {
 563     if ( nStart == npos )
 564     {
 565         nStart = length();
 566     }
 567     else
 568     {
 569         wxASSERT( nStart <= length() );
 570     }
 571
 572     const wxStringCharType *actual;
 573     for ( actual = c_str() + ( nStart == npos ? length() : nStart + 1 );
 574           actual > c_str(); --actual )
 575     {
 576         if ( *(actual - 1) == ch )
 577             return (actual - 1) - c_str();
 578     }
 579
 580     return npos;
 581 }
 582
 583 wxStringImpl& wxStringImpl::replace(size_t nStart, size_t nLen,
 584                                     const wxStringCharType *sz, size_t nCount)
 585 {
 586     // check and adjust parameters
 587     const size_t lenOld = length();
 588
 589     wxASSERT_MSG( nStart <= lenOld,
 590                   wxT("index out of bounds in wxStringImpl::replace") );
 591     size_t nEnd = nStart + nLen;
 592     if ( nLen > lenOld - nStart )
 593     {
 594         // nLen may be out of range, as it can be npos, just clump it down
 595         nLen = lenOld - nStart;
 596         nEnd = lenOld;
 597     }
 598
 599     if ( nCount == npos )
 600         nCount = wxStrlen(sz);
 601
 602     // build the new string from 3 pieces: part of this string before nStart,
 603     // the new substring and the part of this string after nStart+nLen
 604     wxStringImpl tmp;
 605     const size_t lenNew = lenOld + nCount - nLen;
 606     if ( lenNew )
 607     {
 608         tmp.AllocBuffer(lenOld + nCount - nLen);
 609
 610         wxStringCharType *dst = tmp.m_pchData;
 611         memcpy(dst, m_pchData, nStart*sizeof(wxStringCharType));
 612         dst += nStart;
 613
 614         memcpy(dst, sz, nCount*sizeof(wxStringCharType));
 615         dst += nCount;
 616
 617         memcpy(dst, m_pchData + nEnd, (lenOld - nEnd)*sizeof(wxStringCharType));
 618     }
 619
 620     // and replace this string contents with the new one
 621     swap(tmp);
 622     return *this;
 623 }
 624
 625 wxStringImpl wxStringImpl::substr(size_t nStart, size_t nLen) const
 626 {
 627   if ( nLen == npos )
 628     nLen = length() - nStart;
 629   return wxStringImpl(*this, nStart, nLen);
 630 }
 631
 632 // assigns one string to another
 633 wxStringImpl& wxStringImpl::operator=(const wxStringImpl& stringSrc)
 634 {
 635   wxASSERT( stringSrc.GetStringData()->IsValid() );
 636
 637   // don't copy string over itself
 638   if ( m_pchData != stringSrc.m_pchData ) {
 639     if ( stringSrc.GetStringData()->IsEmpty() ) {
 640       Reinit();
 641     }
 642     else {
 643       // adjust references
 644       GetStringData()->Unlock();
 645       m_pchData = stringSrc.m_pchData;
 646       GetStringData()->Lock();
 647     }
 648   }
 649
 650   return *this;
 651 }
 652
 653 // assigns a single character
 654 wxStringImpl& wxStringImpl::operator=(wxStringCharType ch)
 655 {
 656   wxStringCharType c(ch);
 657   if ( !AssignCopy(1, &c) ) {
 658     wxFAIL_MSG( wxT("out of memory in wxStringImpl::operator=(wxStringCharType)") );
 659   }
 660   return *this;
 661 }
 662
 663 // assigns C string
 664 wxStringImpl& wxStringImpl::operator=(const wxStringCharType *psz)
 665 {
 666   if ( !AssignCopy(wxStrlen(psz), psz) ) {
 667     wxFAIL_MSG( wxT("out of memory in wxStringImpl::operator=(const wxStringCharType *)") );
 668   }
 669   return *this;
 670 }
 671
 672 // helper function: does real copy
 673 bool wxStringImpl::AssignCopy(size_t nSrcLen,
 674                               const wxStringCharType *pszSrcData)
 675 {
 676   if ( nSrcLen == 0 ) {
 677     Reinit();
 678   }
 679   else {
 680     if ( !AllocBeforeWrite(nSrcLen) ) {
 681       // allocation failure handled by caller
 682       return false;
 683     }
 684     memcpy(m_pchData, pszSrcData, nSrcLen*sizeof(wxStringCharType));
 685     GetStringData()->nDataLength = nSrcLen;
 686     m_pchData[nSrcLen] = wxT('\0');
 687   }
 688   return true;
 689 }
 690
 691 // ---------------------------------------------------------------------------
 692 // string concatenation
 693 // ---------------------------------------------------------------------------
 694
 695 // add something to this string
 696 bool wxStringImpl::ConcatSelf(size_t nSrcLen,
 697                               const wxStringCharType *pszSrcData,
 698                               size_t nMaxLen)
 699 {
 700   STATISTICS_ADD(SummandLength, nSrcLen);
 701
 702   nSrcLen = nSrcLen < nMaxLen ? nSrcLen : nMaxLen;
 703
 704   // concatenating an empty string is a NOP
 705   if ( nSrcLen > 0 ) {
 706     wxStringData *pData = GetStringData();
 707     size_t nLen = pData->nDataLength;
 708
 709     // take special care when appending part of this string to itself: the code
 710     // below reallocates our buffer and this invalidates pszSrcData pointer so
 711     // we have to copy it in another temporary string in this case (but avoid
 712     // doing this unnecessarily)
 713     if ( pszSrcData >= m_pchData && pszSrcData < m_pchData + nLen )
 714     {
 715         wxStringImpl tmp(pszSrcData, nSrcLen);
 716         return ConcatSelf(nSrcLen, tmp.m_pchData, nSrcLen);
 717     }
 718
 719     size_t nNewLen = nLen + nSrcLen;
 720
 721     // alloc new buffer if current is too small
 722     if ( pData->IsShared() ) {
 723       STATISTICS_ADD(ConcatHit, 0);
 724
 725       // we have to allocate another buffer
 726       wxStringData* pOldData = GetStringData();
 727       if ( !AllocBuffer(nNewLen) ) {
 728           // allocation failure handled by caller
 729           return false;
 730       }
 731       memcpy(m_pchData, pOldData->data(), nLen*sizeof(wxStringCharType));
 732       pOldData->Unlock();
 733     }
 734     else if ( nNewLen > pData->nAllocLength ) {
 735       STATISTICS_ADD(ConcatHit, 0);
 736
 737       reserve(nNewLen);
 738       // we have to grow the buffer
 739       if ( capacity() < nNewLen ) {
 740           // allocation failure handled by caller
 741           return false;
 742       }
 743     }
 744     else {
 745       STATISTICS_ADD(ConcatHit, 1);
 746
 747       // the buffer is already big enough
 748     }
 749
 750     // should be enough space
 751     wxASSERT( nNewLen <= GetStringData()->nAllocLength );
 752
 753     // fast concatenation - all is done in our buffer
 754     memcpy(m_pchData + nLen, pszSrcData, nSrcLen*sizeof(wxStringCharType));
 755
 756     m_pchData[nNewLen] = wxT('\0');          // put terminating '\0'
 757     GetStringData()->nDataLength = nNewLen; // and fix the length
 758   }
 759   //else: the string to append was empty
 760   return true;
 761 }
 762
 763 // get the pointer to writable buffer of (at least) nLen bytes
 764 wxStringCharType *wxStringImpl::DoGetWriteBuf(size_t nLen)
 765 {
 766   if ( !AllocBeforeWrite(nLen) ) {
 767     // allocation failure handled by caller
 768     return NULL;
 769   }
 770
 771   wxASSERT( GetStringData()->nRefs == 1 );
 772   GetStringData()->Validate(false);
 773
 774   return m_pchData;
 775 }
 776
 777 // put string back in a reasonable state after GetWriteBuf
 778 void wxStringImpl::DoUngetWriteBuf()
 779 {
 780   DoUngetWriteBuf(wxStrlen(m_pchData));
 781 }
 782
 783 void wxStringImpl::DoUngetWriteBuf(size_t nLen)
 784 {
 785   wxStringData * const pData = GetStringData();
 786
 787   wxASSERT_MSG( nLen < pData->nAllocLength, wxT("buffer overrun") );
 788
 789   // the strings we store are always NUL-terminated
 790   pData->data()[nLen] = wxT('\0');
 791   pData->nDataLength = nLen;
 792   pData->Validate(true);
 793 }
 794
 795 #endif // !wxUSE_STL_BASED_WXSTRING