What is the purpose of a static function in the C language?

In the C language, static functions serve the following purposes:

1. Limiting the scope: Static functions are only visible in the source file where they are defined, and cannot be accessed by other source files. This helps prevent functions from being misused or modified by other files, thus increasing program security.
2. Avoiding naming conflicts: When there are multiple source files with the same function name, declaring one of them as a static function can prevent naming conflicts. Even if both files have static functions with the same name, they are independent and will not interfere with each other.
3. Modular programming: Define functions that are not intended to be called by other files as static functions, and group together similar functions to form a code module. This can improve code readability and maintainability.
4. Optimize performance: Static functions can be called directly without the overhead of function invocation, which improves the efficiency of the program.

In general, static functions are primarily used to limit the scope of functions and avoid naming conflicts, while also helping to improve the readability, maintainability, and execution efficiency of the code.