What is _ in c++

In C, the underscore ('_') is used for: 1. Anonymous variables; 2. Ignore parameters; 3. Macro definition (indicating the current function name); 4. Reserved keywords (override C keywords ); 5. Escape characters (semicolons are ignored); 6. Reserved identifiers (used by the standard library and user libraries).

_ in C In the C programming language, the underscore ('_') has several uses ：

1. Anonymous variable

When declaring a variable, if you do not specify a variable name, you can name it '_':

<code class="cpp">int _ = 5; // 声明一个匿名整型变量并赋予值 5</code>

2. Ignore parameters

In the function parameter list, you can use '_' to ignore unnecessary parameters:

<code class="cpp">void f(int x, int y) {
  int _ = x; // 忽略参数 x
  // ...
}</code>

3. Macro definition

In the preprocessor, the underscore is used to indicate the current function name:

<code class="cpp">#define FUNCNAME __FUNCTION__</code>

4. Some of the reserved keywords

C Keywords may be overridden by user-defined names, in which case '_' can be used instead:

<code class="cpp">#define true _true</code>

5. Escape characters

in string literals , the underscore can be used as an escape character:

<code class="cpp">char greeting[] = "Hello, _World!"; // 添加下划线以忽略分号</code>

6. Reserved identifiers

The standard library and user-defined libraries may use identifiers starting with an underscore. These identifiers are considered reserved and are not recommended for use by users.

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