什么是编译器错误“在令牌之前缺少二进制算子”意思？ [英] What does the compiler error "missing binary operator before token" mean?

问题描述

我最近遇到以下错误尝试使用gcc编译时：

I recently got the following error when trying to compile with gcc:

错误： p>

error: missing binary operator before token "("

Web和SO搜索提供了这个错误的几个具体示例，具体的代码更改来修复它们，但我发现没有一般描述

Web and SO searches came up with several specific examples of this error, with specific code changes to fix them. But I found no general description of what condition causes this error to be issued.

gcc何时以及为什么会产生此错误？

When and why does gcc emit this error?

推荐答案

这不是一个编译器错误，它是一个预处理器错误。似乎当预处理器在尝试评估 #if 或 #elif 指令。

This is not a compiler error, it is a preprocessor error. It seems to occur when the preprocessor encounters invalid syntax while trying to evaluate an expression in a #if or #elif directive.

一个常见的原因是 sizeof 指令

中的 / code>运算符例如：

For example:

  #define NBITS (sizeof(TYPE)*8)
  //later
  #if (NBITS>16)    //ERROR

这是一个错误，因为 sizeof 由编译器评估，而不是预处理器。

This is an error because sizeof is evaluated by the compiler, not the preprocesor.

类型转换也不是有效的预处理语法：

Type casts are also not valid preprocessor syntax:

  #define ALLBITS ((unsigned int) -1)
  //later
  #if (ALLBITS>0xFFFF)    //ERROR

有效表达式中的规则

The rules for what can be in a valid expression are here.

请注意， #if 会将未定义的宏评估为0，除非看起来像它需要参数，在这种情况下，您也会收到此错误：

Note also that #if will evaluate an undefined macro as 0, unless it looks like it takes arguments, in which case you also get this error:

因此，如果 THIS 未定义：

#if THIS == 0  //valid, true

#if THIS > 0 //valid, false

#if THIS() == 0  //invalid. ERROR

您的 #if 语句中的错字也可能导致此消息。

Typos in your #if statement can also cause this message.

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