SQLite

  if( p->mxAlloc==0 ){
    N = p->nAlloc - p->nChar - 1;
    setStrAccumError(p, STRACCUM_TOOBIG);
    return N;
  }else{
    char *zOld = isMalloced(p) ? p->zText : 0;
    i64 szNew = p->nChar;
    assert( (p->zText==0 || p->zText==p->zBase)==!isMalloced(p) );
    szNew += N + 1;
    if( szNew+p->nChar<=p->mxAlloc ){
      /* Force exponential buffer size growth as long as it does not overflow,
      ** to avoid having to call this routine too often */
      szNew += p->nChar;
    }
    if( szNew > p->mxAlloc ){

** Append N copies of character c to the given string buffer.
*/
void sqlite3AppendChar(StrAccum *p, int N, char c){
  testcase( p->nChar + (i64)N > 0x7fffffff );
  if( p->nChar+(i64)N >= p->nAlloc && (N = sqlite3StrAccumEnlarge(p, N))<=0 ){
    return;
  }
  assert( (p->zText==p->zBase)==!isMalloced(p) );
  while( (N--)>0 ) p->zText[p->nChar++] = c;
}

/*
** The StrAccum "p" is not large enough to accept N new bytes of z[].
** So enlarge if first, then do the append.
**
** This is a helper routine to sqlite3StrAccumAppend() that does special-case
** work (enlarging the buffer) using tail recursion, so that the
** sqlite3StrAccumAppend() routine can use fast calling semantics.
*/
static void SQLITE_NOINLINE enlargeAndAppend(StrAccum *p, const char *z, int N){
  N = sqlite3StrAccumEnlarge(p, N);
  if( N>0 ){
    memcpy(&p->zText[p->nChar], z, N);
    p->nChar += N;
  }
  assert( (p->zText==0 || p->zText==p->zBase)==!isMalloced(p) );
}

/*
** Append N bytes of text from z to the StrAccum object.  Increase the
** size of the memory allocation for StrAccum if necessary.
*/
void sqlite3StrAccumAppend(StrAccum *p, const char *z, int N){

/*
** Finish off a string by making sure it is zero-terminated.
** Return a pointer to the resulting string.  Return a NULL
** pointer if any kind of error was encountered.
*/
static SQLITE_NOINLINE char *strAccumFinishRealloc(StrAccum *p){

  assert( p->mxAlloc>0 && !isMalloced(p) );
  p->zText = sqlite3DbMallocRaw(p->db, p->nChar+1 );
  if( p->zText ){
    memcpy(p->zText, p->zBase, p->nChar+1);
    p->printfFlags |= SQLITE_PRINTF_MALLOCED;
  }else{
    setStrAccumError(p, STRACCUM_NOMEM);
  }

  return p->zText;
}
char *sqlite3StrAccumFinish(StrAccum *p){
  if( p->zText ){
    assert( (p->zText==p->zBase)==!isMalloced(p) );
    p->zText[p->nChar] = 0;
    if( p->mxAlloc>0 && !isMalloced(p) ){
      return strAccumFinishRealloc(p);
    }
  }
  return p->zText;
}

/*
** Reset an StrAccum string.  Reclaim all malloced memory.
*/
void sqlite3StrAccumReset(StrAccum *p){
  assert( (p->zText==0 || p->zText==p->zBase)==!isMalloced(p) );
  if( isMalloced(p) ){
    sqlite3DbFree(p->db, p->zText);
    p->printfFlags &= ~SQLITE_PRINTF_MALLOCED;
  }
  p->zText = 0;
}

**        is malloced.
** n:     Size of zBase in bytes.  If total space requirements never exceed
**        n then no memory allocations ever occur.
** mx:    Maximum number of bytes to accumulate.  If mx==0 then no memory
**        allocations will ever occur.
*/
void sqlite3StrAccumInit(StrAccum *p, sqlite3 *db, char *zBase, int n, int mx){
  p->zText = p->zBase = zBase;
  p->db = db;
  p->nChar = 0;
  p->nAlloc = n;
  p->mxAlloc = mx;

  p->accError = 0;
  p->printfFlags = 0;
}

/*
** Print into memory obtained from sqliteMalloc().  Use the internal
** %-conversion extensions.

/*
** An objected used to accumulate the text of a string where we
** do not necessarily know how big the string will be in the end.
*/
struct StrAccum {
  sqlite3 *db;         /* Optional database for lookaside.  Can be NULL */
  char *zBase;         /* A base allocation.  Not from malloc. */
  char *zText;         /* The string collected so far */
  u32  nChar;          /* Length of the string so far */
  u32  nAlloc;         /* Amount of space allocated in zText */
  u32  mxAlloc;        /* Maximum allowed allocation.  0 for no malloc usage */

  u8   accError;       /* STRACCUM_NOMEM or STRACCUM_TOOBIG */
  u8   printfFlags;    /* SQLITE_PRINTF flags below */
};
#define STRACCUM_NOMEM   1
#define STRACCUM_TOOBIG  2
#define SQLITE_PRINTF_INTERNAL 0x01  /* Internal-use-only converters allowed */
#define SQLITE_PRINTF_SQLFUNC  0x02  /* SQL function arguments to VXPrintf */