PCF8574Write(B11111110);
what command is it? a function from you? from a library?
if you have to copy bytes to/from a vector, use the memcpy() standard C function. reference: http://www.cplusplus.com/reference/clibrary/cstring/memcpy/
maybe
memcpy(PCFStatus1, mb_mapping->tab_coil_status, n);
bye
quark