Most compilers have directives for packing structs. What the OP suggests is something that can be done for high performance, but don't expect it to be portable

Most compilers have directives for packing structs. What the OP suggests is something that can be done for high performance, but don't expect it to be portable outside of common architectures and compilers. I'd consider it something that shouldn't be done unless you really need the simplicity or performance.