c - 为什么在#include 之前需要#？

Question

#的作用是什么？

Answer 1

它denotes a preprocessor directive :

One important thing you need to remember is that the C preprocessor is not part of the C compiler.

The C preprocessor uses a different syntax. All directives in the C preprocessor begin with a pound sign (#). In other words, the pound sign denotes the beginning of a preprocessor directive, and it must be the first nonspace character on the line.

# 可能被任意选择为 C 语法中未使用的字符。我想 @ 也能正常工作。

如果没有字符表示它，那么区分用于预处理器的代码可能会遇到麻烦——您如何判断 if (FOO) 是要预处理还是不是吗？