Fortran is a general-purpose, compiled imperative programming language that is especially suited to numeric computation and scientific computing. It was originally developed by IBM in the 1950s for scientific and engineering applications.
Fortran Anti-Patterns Overview
Fortran, despite being one of the oldest programming languages still in active use, has several common anti-patterns that can lead to performance issues, maintainability problems, and bugs. Here are the most important anti-patterns to avoid when writing Fortran code.
Using GOTO Statements
Avoid using GOTO
statements, which make code difficult to understand and maintain. Use structured control flow constructs like DO
loops, IF-THEN-ELSE
, and SELECT CASE
instead.
Not Using IMPLICIT NONE
Always use IMPLICIT NONE
to disable implicit typing. This helps catch typos and undeclared variables at compile time, making your code more robust.
Using COMMON Blocks
Avoid using COMMON
blocks for sharing data between program units. Use modules instead, which provide better type checking, encapsulation, and maintainability.
Using Fixed-Form Source
Use free-form source format (introduced in Fortran 90) instead of the older fixed-form format. Free-form is more readable, flexible, and doesn’t have column restrictions.
Using Obsolete Features
Avoid using obsolete features like labeled DO loops, arithmetic IF statements, and computed GOTO. Use modern control structures that are more readable and maintainable.
Not Using Modules for Data Encapsulation
Use modules to encapsulate data and related procedures. This improves code organization, maintainability, and helps prevent unintended modifications to data.
Using EQUIVALENCE Statement
Avoid using the EQUIVALENCE
statement, which can lead to undefined behavior and makes code hard to understand and maintain. Use explicit type conversions or derived types instead.
Not Using Proper Array Operations
Use Fortran’s array operations instead of explicit loops for element-by-element operations. Array operations are more concise, often more efficient, and can be automatically parallelized by the compiler.
Not Using Allocatable Arrays
Use allocatable arrays instead of fixed-size arrays when the size is not known at compile time. This avoids wasting memory and potential buffer overflows.
Not Using INTENT Attributes
Always use INTENT
attributes (IN
, OUT
, INOUT
) for subroutine and function arguments. This documents how arguments are used, helps prevent bugs, and enables compiler optimizations.
Using ENTRY Statement
Avoid using the ENTRY
statement, which creates multiple entry points in a single subroutine or function. This makes code hard to understand and maintain. Use separate subroutines or functions instead.
Not Using Proper Error Handling
Use proper error handling for I/O operations and other potential sources of errors. Check status codes (IOSTAT
) and provide meaningful error messages (IOMSG
).
Not Using KIND Parameters
Use KIND
parameters to specify precision requirements in a portable way. This makes your code more maintainable and portable across different platforms.
Not Using Proper File Handling
Use NEWUNIT
to get a unique unit number instead of hardcoding unit numbers. Also, always check for I/O errors and handle them appropriately.
Not Using Proper Initialization
Always initialize variables before using them. Uninitialized variables can contain unpredictable values, leading to bugs that are hard to track down.
Not Using Proper Derived Types
Use derived types to group related data together. This makes code more organized, readable, and maintainable, especially for complex data structures.
Not Using Proper Documentation
Document your code with comments that explain the purpose, parameters, return values, and any important details or assumptions. This makes your code more maintainable and easier for others (including your future self) to understand.
Not Using Proper Testing
Write automated tests for your code to verify that it works correctly. This helps catch bugs early and ensures that your code continues to work as expected when you make changes.