c++ - float bits and strict aliasing -

i trying extract bits float without invoking undefined behavior. here first attempt:

unsigned foo(float x) {     unsigned* u = (unsigned*)&x;     return *u; } 

as understand it, not guaranteed work due strict aliasing rules, right? work if take intermediate step character pointer?

unsigned bar(float x) {     char* c = (char*)&x;     unsigned* u = (unsigned*)c;     return *u; } 

or have extract individual bytes myself?

unsigned baz(float x) {     unsigned char* c = (unsigned char*)&x;     return c[0] | c[1] << 8 | c[2] << 16 | c[3] << 24; } 

of course has disadvantage of depending on endianness, live that.

the union hack undefined behavior, right?

unsigned uni(float x) {     union { float f; unsigned u; };     f = x;     return u; } 

just completeness, here reference version of foo. undefined behavior, right?

unsigned ref(float x) {     return (unsigned&)x; } 

so, possible extract bits float (assuming both 32 bits wide, of course)?

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edit: , here memcpy version proposed goz. since many compilers not support static_assert yet, have replaced static_assert template metaprogramming:

template <bool, typename t> struct requirement;  template <typename t> struct requirement<true, t> {     typedef t type; };  unsigned bits(float x) {     requirement<sizeof(unsigned)==sizeof(float), unsigned>::type u;     memcpy(&u, &x, sizeof u);     return u; } 

about way avoid issues memcpy.

unsigned int floattoint( float f ) {    static_assert( sizeof( float ) == sizeof( unsigned int ), "sizes must match" );    unsigned int ret;    memcpy( &ret, &f, sizeof( float ) );    return ret; } 

because memcpying fixed amount compiler optimise out.

that said union method supported.