What does c language @ mean?

The meaning of @ symbol in C language includes: pointing to variable address, format string, specified attribute, preprocessor directive, GCC extension (such as printing file name, line number and function name).

Meaning of @ in C language

@ symbol in C language has multiple meanings depending on its location of use.

1. Point to the address of a variable

When @ is used as a unary operator, it returns the address of its operand variable. For example:

<code class="c">int x = 5;
int *ptr = &x;  // ptr 指向 x 的地址</code>

2. Format string

Use the @ symbol to specify a format string for formatted output. For example:

<code class="c">printf("%@d", x);  // 以十进制格式打印 x</code>

3. Attributes

In C99 and later, the @ symbol can be used to specify attributes of a function or variable. For example:

<code class="c">@noreturn int my_function();  // 指示 my_function() 函数将不返回</code>

4. Preprocessor directives

In the C preprocessor, the @ symbol is used to specify preprocessor directives. For example:

<code class="c">#define PI 3.14159265  // 定义一个常量</code>

5. GCC extensions

The GCC compiler provides several @ extensions:

• @file: Print the current file name
• @line: Print the current line number
• @function: Print the current function name

These extensions are only available in the GCC compiler.

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