int TForm1::decode_b64(const unsigned char *buftodec, int bufsize,
	unsigned char *decbuf) {
 // выделяем память под временный буфер
 unsigned char *buftemp = new unsigned char[bufsize];
 memset(buftemp, '\0', bufsize);
 memcpy(buftemp, buftodec, bufsize);

 int i = 0;
 int cpos[5];
 unsigned char binbyte[4];

 while (i < bufsize) {
  if (buftemp[i] == '=')
   cpos[0] = 0;
  else
   cpos[0] = strchr(Base64Table, buftemp[i]) - Base64Table;

  if (buftemp[i + 1] == '=')
   cpos[1] = 0;
  else
   cpos[1] = strchr(Base64Table, buftemp[i + 1]) - Base64Table;

  if (buftemp[i + 2] == '=')
   cpos[2] = 0;
  else
   cpos[2] = strchr(Base64Table, buftemp[i + 2]) - Base64Table;

  if (buftemp[i + 3] == '=')
   cpos[3] = 0;
  else
   cpos[3] = strchr(Base64Table, buftemp[i + 3]) - Base64Table;

  binbyte[0] = ((cpos[0] << 2) | (cpos[1] >> 4));
  binbyte[1] = ((cpos[1] << 4) | (cpos[2] >> 2));
  binbyte[2] = (((cpos[2] & 0x03) << 6) | (cpos[3] & 0x3f));
  decbuf[i - (i / 4)] = binbyte[0];
  decbuf[i - (i / 4) + 1] = binbyte[1];
  decbuf[i - (i / 4) + 2] = binbyte[2];
  i += 4;
 }

 delete buftemp;
 return strlen(decbuf);
}

void __fastcall TForm1::Button1Click(TObject *Sender) {
 unsigned char* src = "\"PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0id2luZG93cy0xMjUxIj8+PNTg6esgwuXw8dTu8Ow9IjUuMDEiPj";
 unsigned char* dst = new unsigned char[92];
 memset(dst, '\0', 92);
 decode_b64(src, 92, dst);
 // dst = \x10рэбµ°ЃЩ•ЙНҐЅёф€ДёА€Ѓ•№ЌЅ‘Ґ№њф‰ЭҐ№‘ЅЭМґДИФД€ьшуSѓ§¬ѓ\v—ГЗS»Г°ф€ФёАД€шА 
 Caption = "";
}

#include <EncdDecd.hpp>

void __fastcall TForm1::Button1Click(TObject *Sender) {
 wchar_t* s = L"\"PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0id2luZG93cy0xMjUxIj8+PNTg6esgwuXw8dTu8Ow9IjUuMDEiPj";
 wchar_t* d = DecodeString(s).c_str(); // тут получаю ошибку  см. скриншот
 Caption = "";
}

uses EncdDecd
 
procedure TForm1.Button1Click(Sender: TObject);
 const s = '"PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0id2luZG93cy0xMjUxIj8+PNTg6esgwuXw8dTu8Ow9IjUuMDEiPj';
 var
 d: string;
begin
 d := DecodeString(s);
 Caption := '';
end;