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