有符号/无符号比较和-Wall [英] Signed / unsigned comparison and -Wall

问题描述

我最近开始使用-Wall编译器开关，试图提高我的代码的质量。

  int i; 
 
 for（i = start-1; i> = 0; i--）
 {
 if（i> = number1.array.size（））
 {
 one_value = 0; 
} 
  

因为number1.array.size是无符号的：：向量）。由于循环中的测试是i> = 0，我必须签名或不工作。看来我有三个选择;避免使用-Wall，忽略警告或引入辅助元素...

  int i; 
 unsigned int j; 
 
 for（i = start-1; i> = 0; i--）
 {
 j = 
 
 if（j> = number1.array.size（））
 {
 one_value = 0; 
} 
  

这些都不是特别可取的。

解决方案

因为测试在这个案件中应该做什么？循环是i> = 0，我必须签名或它不工作。只需更改您的测试，如下：

  for（unsigned i = start; i--;）{
 // ... 
} 
  

在循环体中给出相同的i值。 / p>

I have recently started using the -Wall compiler switch in an attempt to improve the quality of my code. It is giving (correctly) a warning about this little snippet...

    int i;

    for (i = start - 1; i >= 0; i--)
    {
        if (i >= number1.array.size())
        {
            one_value = 0;
        }

because number1.array.size is unsigned (it's the size method on a std::vector). Since the test in the loop is i >= 0, i has to be signed or it doesn't work. It seems I have three choices; to refrain from using -Wall, to ignore the warning, or to introduce an ancillary element...

    int          i;
    unsigned int j;

    for (i = start - 1; i >= 0; i--)
    {
        j = i;

        if (j >= number1.array.size())
        {
            one_value = 0;
        }

None of these seems particularly desirable. Can you suggest any alternative, or make a recommendation as to what I should do in this case?

解决方案

"Since the test in the loop is i >= 0, i has to be signed or it doesn't work." Just change your test like this:

for(unsigned i = start; i--;) {
    // ...
}

Gives you the same value of i in the loop body.

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