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Program libraries

What is a program library?

  • A program library is a collection of pre-written code (called library routines) that programmers can reuse in their own software

  • These routines can perform common tasks such as:

    • Sorting

    • Displaying graphics

    • Playing sounds

    • Managing data

  • Advantages of using program libraries includes:

Advantage

Explanation

Saves development time

Pre-written routines can be reused, so programmers don’t need to write common functions from scratch

Promotes code reuse

Well-tested routines can be used in multiple programs, reducing duplication

Improves reliability

Library routines are usually thoroughly tested and debugged, reducing the chance of errors

Easier maintenance

Updates to a library routine automatically benefit all programs that use it (especially with DLLs)

Efficient memory usage

Dynamic link libraries (DLLs) are only loaded when needed at runtime, saving system resources

Standardisation

Promotes consistency in how common tasks (e.g. file handling, sorting) are implemented

What is a DLL?

  • A Dynamic Link Library (DLL) is a file that contains pre-written code, such as functions or routines, that can be used by multiple programs at runtime

Aspect

Advantages

Disadvantages

Program Size

Reduces program size by keeping reusable code separate

Memory Usage

Saves memory by sharing DLLs between programs

Code Reuse

Encourages reuse of common routines (e.g. sorting, sound)

Modularity

Supports modular design for easier development and maintenance

Ease of Updates

Update a DLL once to improve all programs that use it

Can cause version conflicts if newer DLLs aren’t compatible

Dependencies

External DLLs can be reused by many applications

Program may fail to run if a required DLL is missing

Security

Malicious or altered DLLs can pose security risks

Debugging

Errors in DLLs can be hard to trace across multiple programs

Worked Example

Jennifer is writing a computer program for her A Level homework.

Jennifer uses a program library to help her write her computer program.

Describe how a program library can be used while writing a computer program. [2]

Answer

  • Program libraries store pre-written functions and routines [1 mark]

  • The program library can be referenced/imported [1 mark]

  • The functions/routines can be called in her own program [1 mark]

Responses

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