Binary template for reading strings of known or unknown length

prelen.bt

//--------------------------------------
//--- 010 Editor v5.0.0 Binary Template
//
// File:      prelen.bt
// Author:    x1nixmzeng/WRS
// Revision:  v1.03
// Purpose:   Reading strings of known length
// History
//  v1.03     Added optional STR_ENCODING macro to specify the charset
//            used to format the template results
//            Added optional PRELEN_REQUIRE macro for future versions
//  v1.02     Added new alignment type for null-length strings
//  v1.01     Added guards to avoid errors when included more than once
//  v1.00     NOTE: The prelenType enum values have been updated
//            NOTE: Unicode strings have been separately defined (wstr)
//            Supports
//             * 32/16/8 size descriptions
//             * Null-terminated strings
//             * Fixed length strings
//  ------------------------------------
//  v0.05     Now supports strings of known length
//  v0.04     Added support for null-terminated strings
//  v0.03     Added supported for wide strings (prepend 'w' to prelenType)
//  v0.02     strRead function replaced with GetStrValue
//            Cleaner GetStrValue method
//            String displayed for empty values can now be defined outside script
//--------------------------------------
#ifndef PRELEN_BT_
#define PRELEN_BT_

#define PRELEN_VERSION 103

RequiresVersion(5);

#ifndef STR_EMPTY
  // Default value used for empty values
  #define STR_EMPTY ""
#endif

#ifndef STR_ENCODING
  // Default source encoding
  #define STR_ENCODING GetFileCharSet()
#endif

#ifdef PRELEN_REQUIRE
if(PRELEN_REQUIRE > PRELEN_VERSION)
{
  Warning("Version %u of prelen.bt is required (have %u)", PRELEN_REQUIRE, PRELEN_VERSION);
  Exit(-1);
}
#endif

//#define PRELEN_DISABLE_CHECKS

// Length flags
enum prelenType
{
  pnt8   = -6, // null-terminated size descriptor, string padded to 8 bytes
  pnt4   = -5, // null-terminated size descriptor, string padded to 4 bytes
  plen32 = -4, // 32-bit size descriptor
  plen16 = -3, // 16-bit size descriptor
  plen8  = -2, // 8-bit size descriptor
  pnt    = -1, // null-terminated size descriptor
  pblank = 0   // Empty string
};

//
// Helpers
//

int Align(int val, int align)
{
  return ((val+(align-1)) & (~(align-1))) - val;
}

//
// Structures
//

// ASCII
struct prelenStr( prelenType t )
{
  if( t == pblank )
  {
    // NOTE: This will give an empty structure warning
    local uint len = 0;
  }
  else
  {
    if( t > pblank )
    {
      local uint len = t;
      char val[len];
    }
    else
    if( t == pnt || t == pnt4 || t == pnt8 )
    {
      string val;
      local uint len = Strlen( val );

      if( len > 0 && t != pnt )
      {
        local int pad = 0;
        local uint size = len +1;

        switch( t )
        {
          case pnt4 : pad = Align(size, 4);  break;
          case pnt8 : pad = Align(size, 8);  break;
        }

        if( pad > 0 )
          FSkip( pad );
      }
    }
    else
    {
      switch( t )
      {
        case plen32  : uint   len; break;
        case plen16  : ushort len; break;
        case plen8   : ubyte  len; break;
        default      : Assert( false, "Unknown prelenType" );
      }

#ifndef PRELEN_DISABLE_CHECKS
      if( FTell() + len > FileSize() )
        Warning("prelen.bt :: String out of bounds");
#endif

      if( len > 0 )
        char val[len];
    }
  }
};

// Unicode
struct prelenWStr( prelenType t )
{
  if( t == pblank )
  {
    // NOTE: This will give an empty structure warning
    local uint len = 0;
  }
  else
  {
    if( t > pblank )
    {
      local uint len = t;
      wchar_t val[len];
    }
    else
    if( t == pnt || t == pnt4 || t == pnt8 )
    {
      wstring val;
      local uint len = WStrlen( val );

      if( len > 0 && t != pnt )
      {
        local int pad = 0;
        local uint size = (len +1) * sizeof(wchar_t);

        switch( t )
        {
          case pnt4 : pad = Align(size, 4);  break;
          case pnt8 : pad = Align(size, 8);  break;
        }

        if( pad > 0 )
          FSkip( pad );
      }
    }
    else
    {
      switch( t )
      {
        case plen32  : uint   len; break;
        case plen16  : ushort len; break;
        case plen8   : ubyte  len; break;
        default      : Assert( false, "Unknown prelenType" );
      }

      if( len > 0 )
        wchar_t val[len];
    }
  }
};


//
// Type definitions
//

// ASCII
typedef prelenStr  str  <read=GetStrValue >;
// Unicode
typedef prelenWStr wstr <read=GetWStrValue>;


//
// Accessor functions
//

// ASCII
wstring GetStrValue(str &t)
{
  // Return string or empty string
  return( t.len ? StringToWString(t.val, STR_ENCODING) : STR_EMPTY );
}

// Unicode
wstring GetWStrValue(wstr &t)
{
  // Return string or empty string
  return( t.len ? t.val : STR_EMPTY );
}

#endif
// EOF

Updated to v1.03 which includes an optional macro for target character set (for display in the template results). Example usage:

#define STR_ENCODING CHARSET_CHINESE_S
#include "prelen.bt"

str ChineseString(plen32);