Poor Style: Variable Never Used

C/C++
Solidity

Abstract

此變數從未被使用過。

Explanation

此變數從未被使用過。可能這只是一個無用的程式碼，但是這也可能指出了一個錯誤。

範例：在以下程式碼中，一個複製貼上錯誤導致相同的迴圈迭代器 (i) 被使用了兩次。變數 j 從未使用過。


  int i,j;

  for (i=0; i < outer; i++) {
    for (i=0; i < inner; i++) {
      ...

References

[1] Standards Mapping - CIS Azure Kubernetes Service Benchmark 1

[2] Standards Mapping - CIS Amazon Elastic Kubernetes Service Benchmark 4

[3] Standards Mapping - CIS Amazon Web Services Foundations Benchmark 1

[4] Standards Mapping - CIS Google Kubernetes Engine Benchmark normal

[5] Standards Mapping - Common Weakness Enumeration CWE ID 563

[6] Standards Mapping - Motor Industry Software Reliability Association (MISRA) C++ Guidelines 2008 Rule 0-1-3

[7] Standards Mapping - Security Technical Implementation Guide Version 3.1 APP3050 CAT II

[8] Standards Mapping - Security Technical Implementation Guide Version 3.4 APP3050 CAT II

[9] Standards Mapping - Security Technical Implementation Guide Version 3.5 APP3050 CAT II

[10] Standards Mapping - Security Technical Implementation Guide Version 3.6 APP3050 CAT II

[11] Standards Mapping - Security Technical Implementation Guide Version 3.7 APP3050 CAT II

[12] Standards Mapping - Security Technical Implementation Guide Version 3.9 APP3050 CAT II

[13] Standards Mapping - Security Technical Implementation Guide Version 3.10 APP3050 CAT II

[14] Standards Mapping - Smart Contract Weakness Classification SWC-131

desc.structural.cpp.poor_style_variable_never_used

Abstract

合約定義了一個變數，但從不使用。

Explanation

Solidity 允許宣告變數、但從不使用，儘管大多數的時候，這並不直接指向安全性弱點，但這是不好的做法。由於所需的運算週期會增加，這可能會導致雜訊和不必要的燃料消耗。

範例 1：以下程式碼宣告類型為 A 的變數 var1，但從不使用。


contract Base {
    struct A { uint a; }
}

contract DerivedA is Base {
    A var1 = A(1);
    int internal j = 500;

    function call(int a) public {
        assign1(a);
    }

    function assign3(A memory x) public returns (uint) {
        return g[1] + x.a + uint(j);
    }
}