此处为操作员的顺序

Order of operators here

本文关键字：顺序 操作员      更新时间：2023-10-16

好的，我需要扩展代码，但这里有一些非常复杂的东西：

((Traces.Last=new SymbolSequence::Node)->Prev=(Discard.First=Processing1)->Prev)->Next=Traces.Last;

我需要将这些作业拆分为语句，但我无法确定顺序。括号里的顺序让我很困惑，这是像数学还是编译器想做什么？

非常感谢。

代码可能是预期的

Traces.Last = new SymbolSequence::Node;
Discard.First = Processing1;
Traces.Last->Prev = Discard.First->Prev;
Traces.Last->Prev->Next = Traces.Last;

然而，由于它都访问Traces.Last并在没有插入序列点的情况下设置它，因此实际结果是未定义的。编译器很有可能会生成以下内容：

temp = Traces.Last;
Traces.Last = new SymbolSequence::Node;
Discard.First = Processing1;
Traces.Last->Prev = Discard.First->Prev;
Traces.Last->Prev->Next = temp;

并且最初的程序员想要类似的东西。

我理解你的痛苦。把整个世界都依赖于一行代码来编写代码的开发人员应该在他们的女朋友面前被打湿面条。

当重构这样的代码时，每次启动一个片段总是很有用的。边走边测试。

取一个位于最内括号组中的小表达式，然后重构它。也许是通过将其分配给一个变量。每个代码都是不同的，所以你可以做你能做的。这将一点一点地缩小那大行代码。继续这样做，直到你的表达式越来越小。这也有助于在运算符之间留出空白，以便实际查看代码的分组，并帮助收集评估顺序。

因此，给定您的原始代码：

((Traces.Last=new SymbolSequence::Node)->Prev=(Discard.First=Processing1)->Prev)->Next=Traces.Last;

将其拆分为：

Traces.Last = new SymbolSequence::Node
((Traces.Last)->Prev = (Discard.First = Processing1)->Prev)->Next = Traces.Last;

现在进行另一项内部任务：

Traces.Last = new SymbolSequence::Node
Discard.First = Processing1
((Traces.Last)->Prev = (Discard.First)->Prev)->Next = Traces.Last;

然后我进行下一个最内层的任务

Traces.Last = new SymbolSequence::Node
Discard.First = Processing1
(Traces.Last)->Prev = (Discard.First)->Prev
( (Traces.Last)->Prev )->Next = Traces.Last;

我希望这能有所帮助。

除了注释中描述的未定义行为之外，下面是根据clang++的AST表示。AST显示运算符在解析时的优先级。

我不得不用一些类型引导您的示例以满足clang++:

struct SymbolSequence
{
    struct Node
    {
        Node *First;
        Node *Last;
        Node *Prev;
        Node *Next;
    };
};
void foo()
{
    SymbolSequence::Node *Processing1;
    SymbolSequence::Node Traces;
    SymbolSequence::Node Discard;
    ((Traces.Last=new SymbolSequence::Node)->Prev=(Discard.First=Processing1)->Prev)->Next=Traces.Last;
}

AST:

void foo() (CompoundStmt 0x308b6e0 <go.cpp:14:1, line:19:1>
  (DeclStmt 0x3088dc8 <line:15:5, col:38>
    (0x3088d70 "SymbolSequence::Node *Processing1"))
  (DeclStmt 0x30891d8 <line:16:5, col:32>
    (0x3088e40 "SymbolSequence::Node Traces =
      (CXXConstructExpr 0x30891a8 <col:26> 'struct SymbolSequence::Node':'struct SymbolSequence::Node''void (void)')"))
  (DeclStmt 0x30892d8 <line:17:5, col:33>
    (0x3089250 "SymbolSequence::Node Discard =
      (CXXConstructExpr 0x30892a8 <col:26> 'struct SymbolSequence::Node':'struct SymbolSequence::Node''void (void)')"))
  (BinaryOperator 0x308b6b8 <line:18:5, col:99> 'struct SymbolSequence::Node *' lvalue '='
    (MemberExpr 0x308b618 <col:5, col:87> 'struct SymbolSequence::Node *' lvalue ->Next 0x3088b60
      (ImplicitCastExpr 0x308b600 <col:5, col:84> 'struct SymbolSequence::Node *' <LValueToRValue>
        (ParenExpr 0x308b5e0 <col:5, col:84> 'struct SymbolSequence::Node *' lvalue
          (BinaryOperator 0x308b5b8 <col:6, col:80> 'struct SymbolSequence::Node *' lvalue '='
            (MemberExpr 0x308b448 <col:6, col:46> 'struct SymbolSequence::Node *' lvalue ->Prev 0x3088b00
              (ImplicitCastExpr 0x308b430 <col:6, col:43> 'struct SymbolSequence::Node *' <LValueToRValue>
                (ParenExpr 0x308b410 <col:6, col:43> 'struct SymbolSequence::Node *' lvalue
                  (BinaryOperator 0x308b3e8 <col:7, col:39> 'struct SymbolSequence::Node *' lvalue '='
                    (MemberExpr 0x3089318 <col:7, col:14> 'struct SymbolSequence::Node *' lvalue .Last 0x3088aa0
                      (DeclRefExpr 0x30892f0 <col:7> 'struct SymbolSequence::Node':'struct SymbolSequence::Node' lvalue Var 0x3088e40 'Traces' 'struct SymbolSequence::Node':'struct SymbolSequence::Node'))
                    (CXXNewExpr 0x308b390 <col:19, col:39> 'struct SymbolSequence::Node *'
                      (CXXConstructExpr 0x308b360 <col:23> 'struct SymbolSequence::Node':'struct SymbolSequence::Node''void (void)'))))))
            (ImplicitCastExpr 0x308b5a0 <col:51, col:80> 'struct SymbolSequence::Node *' <LValueToRValue>
              (MemberExpr 0x308b570 <col:51, col:80> 'struct SymbolSequence::Node *' lvalue ->Prev 0x3088b00
                (ImplicitCastExpr 0x308b558 <col:51, col:77> 'struct SymbolSequence::Node *' <LValueToRValue>
                  (ParenExpr 0x308b538 <col:51, col:77> 'struct SymbolSequence::Node *' lvalue
                    (BinaryOperator 0x308b510 <col:52, col:66> 'struct SymbolSequence::Node *' lvalue '='
                      (MemberExpr 0x308b4a0 <col:52, col:60> 'struct SymbolSequence::Node *' lvalue .First 0x3088a40
                        (DeclRefExpr 0x308b478 <col:52> 'struct SymbolSequence::Node':'struct SymbolSequence::Node' lvalue Var 0x3089250 'Discard' 'struct SymbolSequence::Node':'struct SymbolSequence::Node'))
                      (ImplicitCastExpr 0x308b4f8 <col:66> 'struct SymbolSequence::Node *' <LValueToRValue>
                        (DeclRefExpr 0x308b4d0 <col:66> 'struct SymbolSequence::Node *' lvalue Var 0x3088d70 'Processing1' 'struct SymbolSequence::Node *')))))))))))
    (ImplicitCastExpr 0x308b6a0 <col:92, col:99> 'struct SymbolSequence::Node *' <LValueToRValue>
      (MemberExpr 0x308b670 <col:92, col:99> 'struct SymbolSequence::Node *' lvalue .Last 0x3088aa0
        (DeclRefExpr 0x308b648 <col:92> 'struct SymbolSequence::Node':'struct SymbolSequence::Node' lvalue Var 0x3088e40 'Traces' 'struct SymbolSequence::Node':'struct SymbolSequence::Node')))))
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