为什么要使用“未使用的属性"为结构数组生成警告? [英] Why "unused attribute" generated warning for array of struct?

问题描述

这里使用的是unused具有结构的属性.

Here used, unused attribute with structure.

根据 GCC 文件:

未使用:

此属性附加到变量，表示该变量是 意味着可能未使用. GCC不会对此发出警告 变量.

This attribute, attached to a variable, means that the variable is meant to be possibly unused. GCC will not produce a warning for this variable.

但是，在下面的代码中，结构数组生成了警告.

But, In the following code, array of struct generated warning.

#include <stdio.h>

struct __attribute__ ((unused)) St 
{ 
    int x; 
};

void func1()
{
  struct St s;      // no warning, ok
}

void func2()
{ 
  struct St s[1];   // Why warning???
}

int main() {
    func1();
    func2();
    return 0;
}

为什么GCC会为结构体数组生成警告?

Why does GCC generated warning for array of struct?

推荐答案

您没有将属性附加到变量，而是将其附加到类型.在这种情况下，适用不同的规则:

You are not attaching the attribute to a variable, you are attaching it to a type. In this case, different rules apply:

当附加到类型(包括union或struct)时，此[unused]属性表示该类型的变量可能看起来未使用.即使该变量似乎什么也不做，GCC不会对任何该类型的变量产生警告.

When attached to a type (including a union or a struct), this [unused] attribute means that variables of that type are meant to appear possibly unused. GCC will not produce a warning for any variables of that type, even if the variable appears to do nothing.

这正是func1内部发生的情况:变量struct St s的类型为struct St，因此不会生成警告.

This is exactly what happens inside func1: variable struct St s is of type struct St, so the warning is not generated.

但是，func2是不同的，因为St s[1]的类型不是struct St，而是struct St的数组.此数组类型没有附加特殊属性，因此会生成警告.

However, func2 is different, because the type of St s[1] is not struct St, but an array of struct St. This array type has no special attributes attached to it, hence the warning is generated.

您可以使用typedef将属性添加到特定大小的数组类型:

You can add an attribute to an array type of a specific size with typedef:

typedef __attribute__ ((unused)) struct St ArrayOneSt[1];
...
void func2() { 
  ArrayOneSt s;   // No warning
}

演示.

这篇关于为什么要使用“未使用的属性"为结构数组生成警告?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！