以下cpp表达式中的优先顺序是什么？

Question

uint64_t author.value = 0;
uint64_t timestamp    = 1577369253;    
uint128_t skey = static_cast<uint128_t>(author.value) << 64 | timestamp;

skey的价值是什么？无论时间戳的值如何，我都将其设置为零。可能是什么原因？

Answer 1

uint128_t skey = ( static_cast<uint128_t>(author.value) << 64 ) | timestamp;

优先级
    Parenthesized expression ( expr )
    Lambda [ capture-list ] lambda-declarator { stmt-List }
    Scope resolution class-name :: member
    Scope resolution namespace-name :: member 
    Global :: name
    Each box holds operators with the same precedence. Operators in higher boxes have higher precedence.
    For example, N::x.m means (N::m).m rather than the illegal N::(x.m).256  Expressions  
    Member selection object . member 
    Member selection pointer −> member 
    Subscripting pointer [ expr ]
    Function call expr ( expr-list ) 
    Value construction type { expr-list } §11.3.2
    Function-style type conversion type ( expr-list ) 
    Post increment lvalue ++ 
    Post decrement lvalue −− 
    Type identification typeid ( type ) 
    Run-time type identification typeid ( expr ) 
    Run-time checked conversion dynamic_cast < type > ( expr ) 
    Compile-time checked conversion static_cast < type > ( expr ) §11.5.2
    Unchecked conversion reinterpret_cast < type > ( expr ) §11.5.2
    const conversion const_cast < type > ( expr ) §11.5.2
    Size of object sizeof expr §6.2.8
    Size of type sizeof ( type ) §6.2.8
    Size of parameter pack sizeof... name §28.6.2
    Alignment of type alignof ( type ) §6.2.9
    Pre increment ++ lvalue §11.1.4
    Pre decrement −− lvalue §11.1.4
    Complement ˜ expr §11.1.2
    Not ! expr 
    Unary minus − expr
    Unary plus + expr 
    Address of & lvalue
    Dereference ∗ expr 
    Create (allocate) new type §11.2
    Create (allocate and initialize) new type ( expr-list ) §11.2
    Create (allocate and initialize) new type { expr-list } §11.2
    Create (place) new ( expr-list ) type §11.2.4
    Create (place and initialize) new ( expr-list ) type ( expr-list ) §11.2.4
    Create (place and initialize) new ( expr-list ) type { expr-list } §11.2.4
    Destroy (deallocate) delete pointer §11.2
    Destroy array delete [] pointer §11.2.2
    Can expression throw? noexcept ( expr ) §13.5.1.2
    Cast (type conversion) ( type ) expr §11.5.3
    Member selection object .∗ pointer-to-member §20.6
    Member selection pointer −>∗ pointer-to-member §20.6
    For example, postfix ++ has higher precedence than unary ∗, so ∗p++ means ∗(p++), not (∗p)++.
    Multiply expr ∗ expr §10.2.1
    Divide expr / expr §10.2.1
    Modulo (remainder) expr % expr §10.2.1
    Add (plus) expr + expr §10.2.1
    Subtract (minus) expr − expr §10.2.1
    Shift left expr << expr §11.1.2
    Shift right expr >> expr §11.1.2
    Less than expr < expr §2.2.2
    Less than or equal expr <= expr §2.2.2
    Greater than expr > expr §2.2.2
    Greater than or equal expr >= expr §2.2.2
    Equal expr == expr §2.2.2
    Not equal expr != expr §2.2.2
    Bitwise and expr & expr §11.1.2
    Bitwise exclusive-or expr ˆ expr §11.1.2
    Bitwise inclusive-or expr | expr §11.1.2
    Logical and expr && expr §11.1.1
    Logical inclusive or expr || expr §11.1.1
    Conditional expression expr ? expr : expr 
    List { expr-list } 
    Throw exception throw expr 
    Simple assignment lvalue = expr §10.2.1
    Multiply and assign lvalue ∗= expr §10.2.1
    Divide and assign lvalue /= expr §10.2.1
    Modulo and assign lvalue %= expr §10.2.1
    Add and assign lvalue += expr 
    Subtract and assign lvalue −= expr 
    Shift left and assign lvalue <<= expr 
    Shift right and assign lvalue >>= expr 
    Bitwise and and assign lvalue &= expr 
    Bitwise inclusive-or and assign lvalue |= expr 
    Bitwise exclusive-or and assign lvalue ˆ= expr 
    comma (sequencing) expr , expr

Answer 2

uint128_t skey = (static_cast<uint128_t>(author.value) << 64) | timestamp;

并且据此，按位移位（7）的优先级高于按位或（13）：https://en.cppreference.com/w/cpp/language/operator_precedence