arguments of the sha256 function in Solidity

Question

In Solidity, I find that the sha256 function can be used like this a = sha256(uint b, string c, bool d, ......) (the arguments can be a combination of different types, and the other types can also be included.)

What does sha256 do with the arguments of different types?

Answer 1

Solidity docs say that sha256 (and sha3, ripemd160) arguments are tightly packed:

“tightly packed” means that the arguments are concatenated without padding. This means that the following are all identical:

sha3("ab", "c")

sha3("abc")

sha3(0x616263)

sha3(6382179)

sha3(97, 98, 99)

Using the question's example of a = sha256(uint b, string c, bool d),

• if we assign some values like b is 31415, c is "abc", and d is false,

• then a would equal sha256(31415, 6382179, 0), which is same as sha256(0x7ab761626300).

---

For completeness, the docs mention that:

If padding is needed, explicit type conversions can be used: sha3(“x00x12”) is the same as sha3(uint16(0x12)).