What are the functions of placeholders?

The functions of placeholders are: 1. Used for parameterized queries in database queries; 2. Used to dynamically insert variable values ​​​​in strings; 3. Used to pass parameters or receive function returns. Value; 4. Used to specify a specific format when outputting; 5. During the development process, used as a mark for functions or codes to be implemented.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Placeholder has many uses and functions in programming. The following are the functions of some common placeholders:

1. Parameterized query: Placeholders are often used in parameterized queries in database queries to prevent SQL injection attacks and improve query performance. . By passing variable values ​​as placeholders to the query statement, these values ​​can be inserted dynamically during query execution. This avoids directly splicing user-entered data into query statements, which increases security.

2. String formatting: In string processing, placeholders are used to dynamically insert variable values ​​​​in strings. By using placeholders, you can build complex strings and insert variables, function return values, or the results of other expressions. This makes the code clearer and easier to maintain.

3. Function parameters: Placeholders in a function call are used to pass parameters or receive the return value of the function. Placeholders allow you to pass parameters to a function, which can perform calculations using these parameters and return a result.

4. Format placeholder: During output, placeholders are used to specify a specific format. For example, placeholders used in datetime formatting can define the format in which dates are displayed.

5. To-be-implemented markers: During the development process, placeholders can be used as markers for features or codes to be implemented. They are used to temporarily represent the location of a feature or code and to implement it in subsequent development.

In general, the role of placeholders in programming is to dynamically insert values, parameters, or formats to improve the readability, security, and maintainability of the code. They are widely used in scenarios such as parameterized queries, string formatting, function parameter passing, and marking functions to be implemented.

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