How to Fix a list-directed I/O syntax error While Reading .CSV Files in Fortran90

Discover how to troubleshoot and solve list-directed I/O syntax errors in Fortran90 when reading .CSV files, especially when dealing with problematic data lines.
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Troubleshooting list-directed I/O syntax error in Fortran90

When working with Fortran90 to read .CSV files, you might encounter a frustrating error: the list-directed I/O syntax error. This error can halt your program and leave you confused, particularly if you're dealing with complex .CSV formats. In this post, we will explore the root cause of this error and provide a systematic solution to fix it.

Understanding the Problem

The list-directed I/O syntax error typically occurs when Fortran's read statement encounters a formatting issue it cannot process. In this specific scenario, the error message points to a problematic line in the .CSV file:

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Why Does This Error Occur?

This particular line has issues due to:

Inverted Commas: The presence of a single quote ' within the name field 'Aylo'chaxnim interrupts the expected delimiter flow. Here, Fortran expects a straightforward read of values separated by commas.

List-directed Input Limitation: Fortran’s list-directed input (read(...)) tries to process everything as a simple list. When it encounters a separator that conflicts with this format, it will throw a syntax error.

Solution: Using Custom String Handling

To resolve the list-directed I/O syntax error, you can replace the simplistic read approach with a method that splits the read line into tokens. Here’s how to implement this solution in a step-by-step format:

Step 1: Module for String Splitting

Create a module that can split a string into tokens based on the comma separator. This allows custom handling of quotes and other problematic characters:

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Step 2: Reading CSV Lines

Develop a subroutine that reads each line and separates it into tokens:

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Step 3: Putting It All Together

Finally, in your main program, call the newly created subroutines to read your CSV data properly:

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Conclusion

Switching from list-directed to a tokenized approach allows handling more complex string structures that include unexpected characters. This method ensures that you maintain the original .CSV file format while successfully reading and processing its contents.

With this guide, you should be equipped to tackle list-directed I/O syntax errors in your Fortran90 programs. By implementing these changes, you can read .CSV files accurately and efficiently. Happy coding!