Re: Type-punning / casting problem

Dear Experts,

I need a function that takes a float, swaps its endianness (htonl) in
place, and returns a char* pointer to its first byte. This is one
of a family of functions that prepare different data types for
passing to another process.

I have got confused by the rules about what won't work, what will
work, and what might work, when casting. Specifically, I have an
implementation that works until I remove my debugging, at which point
the compiler seems to decide that it can optimise away the writes to
the bytes other than the first, or something like that. Here it is:

template <typename T>
inline const char* encode_arg(T& t); // linker error if you try to
                                       // encode a type for which
                                       there // is no implementation

// This one works:
template <>
inline const char* encode_pq_arg<int>(int& i) {
   i = htonl(i);
   return reinterpret_cast<const char*>(&i);

}

// This one doesn't:
template <>
inline const char* encode_arg<float>(float& f) {
   uint32_t* ptr = reinterpret_cast<uint32_t*>(&f);
   *ptr = htonl(*ptr);
   const char* cptr = reinterpret_cast<const char*>(ptr);
   return cptr;

}