for (i=0 ;i< len; i++)
    float_buff[i]= (float) char_buff[i];

for (i=0 ;i< len; i++)
    char_buff[i]= (unsigned char) float_buff[i];

char_buff[i]= static_cast<unsigned char>(float_buff[i]);

template <typename T> // T models Any
struct static_cast_func
{
  template <typename T1> // T1 models type statically convertible to T
  T operator()(const T1& x) const { return static_cast<T>(x); }
};

std::transform(char_buff, char_buff + len, float_buff, static_cast_func<float>());
std::transform(float_buff, float_buff + len, char_buff, static_cast_func<unsigned char>());

for (i=0; i< len; i++)
    char_buff[i]= static_cast<unsigned char>(float_buff[i]);

std::copy(char_buff,char_buff+len,float_buff);

std::transform(float_buff,float_buff+len,char_buff,MyTransform());

float *dst = float_buff;
   unsigned char *src = char_buff;

   for (i=0; i<len; i++) *dst++ = (float)*src++;