typedef struct st_dynamic_string
{
 char *str;
 size_t length, max_length, alloc_increment;
} DYNAMIC_STRING;

my_bool init_dynamic_string( DYNAMIC_STRING *str, const char *init_str, size_t init_alloc, size_t alloc_increment )
{
 size_t length;
 DBUG_ENTER( "init_dynamic_string" );
 
 if ( !alloc_increment )
 alloc_increment = 128;
 length = 1;
 if ( init_str && (length = strlen( init_str ) + 1) < init_alloc )
 init_alloc = ( (length + alloc_increment - 1) / alloc_increment) * alloc_increment;
 if ( !init_alloc )
 init_alloc = alloc_increment;
 
 if ( !(str->str = (char *) my_malloc( init_alloc, MYF( MY_WME ) ) ) )
 DBUG_RETURN( TRUE );
 str->length = length - 1;
 if ( init_str )
 memcpy( str->str, init_str, length );
 str->max_length = init_alloc;
 str->alloc_increment = alloc_increment;
 DBUG_RETURN( FALSE );
}

my_bool dynstr_append_mem( DYNAMIC_STRING *str, const char *append, size_t length )
{
 char *new_ptr;
 if ( str->length + length >= str->max_length ) /* 如果新增字符串后，总长度超过缓冲区大小 */
 {
/* 需要分配多少个alloc_increment 大小的内存，才能存下新增后的字符串 */
 size_t new_length = (str->length + length + str->alloc_increment) /
    str->alloc_increment;
 new_length *= str->alloc_increment;
 
 if ( !(new_ptr = (char *) my_realloc( str->str, new_length, MYF( MY_WME ) ) ) )
  return(TRUE);
 str->str = new_ptr;
 str->max_length = new_length;
 }
/* 将新分配的内容，append到str之后 */
 memcpy( str->str + str->length, append, length );
 str->length += length;               /* 扩容之后str新的长度 */
 str->str[str->length] = 0; /* Safety for C programs */    /* 字符串最后一个字符为'\0' */
 return(FALSE);
}

my_bool dynstr_trunc( DYNAMIC_STRING *str, size_t n )
{
 str->length -= n;
 str->str[str->length] = '\0';
 return(FALSE);
}

char *strcend( register const char *s, register pchar c )
{
 for (;; )
 {
 if ( *s == (char) c )
  return( (char *) s);
 if ( !*s++ )
  return( (char *) s - 1);
 }
}

my_bool dynstr_realloc( DYNAMIC_STRING *str, size_t additional_size )
{
 DBUG_ENTER( "dynstr_realloc" );
 
 if ( !additional_size )
 DBUG_RETURN( FALSE );
 if ( str->length + additional_size > str->max_length ) /* 如果新的字符串内容超过缓冲区的最大长度 */
 {
 str->max_length = ( (str->length + additional_size + str->alloc_increment - 1) /
    str->alloc_increment) * str->alloc_increment;
 if ( !(str->str = (char *) my_realloc( str->str, str->max_length, MYF( MY_WME ) ) ) )
  DBUG_RETURN( TRUE );
 }
 DBUG_RETURN( FALSE );
}

/*
 * Concatenates any number of strings, escapes any OS quote in the result then
 * surround the whole affair in another set of quotes which is finally appended
 * to specified DYNAMIC_STRING. This function is especially useful when
 * building strings to be executed with the system() function.
 *
 * @param str Dynamic String which will have addtional strings appended.
 * @param append String to be appended.
 * @param ... Optional. Additional string(s) to be appended.
 *
 * @ note The final argument in the list must be NullS even if no additional
 * options are passed.
 *
 * @return True = Success.
 */
 
my_bool dynstr_append_os_quoted( DYNAMIC_STRING *str, const char *append, ... )
{
 const char *quote_str = "\'";
 const uint quote_len = 1;
 my_bool ret = TRUE;
 va_list dirty_text;
 
 ret &= dynstr_append_mem( str, quote_str, quote_len ); /* Leading quote */
 va_start( dirty_text, append );
 while ( append != NullS )
 {
 const char *cur_pos = append;
 const char *next_pos = cur_pos;
 
/* Search for quote in each string and replace with escaped quote */
 while ( *(next_pos = strcend( cur_pos, quote_str[0] ) ) != '\0' )
 {
  ret &= dynstr_append_mem( str, cur_pos, (uint) (next_pos - cur_pos) );
  ret &= dynstr_append_mem( str, "\\", 1 );
  ret &= dynstr_append_mem( str, quote_str, quote_len );
  cur_pos = next_pos + 1;
 }
 ret &= dynstr_append_mem( str, cur_pos, (uint) (next_pos - cur_pos) );
 append = va_arg( dirty_text, char * );
 }
 va_end( dirty_text );
 ret &= dynstr_append_mem( str, quote_str, quote_len ); /* Trailing quote */
 
 return(ret);
}