CSV file reading and writing in PHP - Step-by-Step Execution

Concept Flow - CSV file reading and writing

Open CSV file

↓

Read line

↓

Parse CSV line

↓

Process data

↓

Repeat until EOF

↓

Close file

↓

Open CSV file for writing

↓

Write data line

↓

Repeat for all lines

↓

Close file

Open a CSV file, read each line parsing CSV data, process it, then close. For writing, open file, write lines, then close.

Execution Sample

PHP

<?php
$handle = fopen('data.csv', 'r');
while (($data = fgetcsv($handle)) !== false) {
    print_r($data);
}
fclose($handle);
?>

This code reads a CSV file line by line and prints each row as an array.

Execution Table

Step	Action	Function Call	Data Read/Write	Output/Result
1	Open file for reading	fopen('data.csv', 'r')	File opened	Resource handle assigned
2	Read first line	fgetcsv(handle)	"John,Doe,30"	Array('John', 'Doe', '30') printed
3	Read second line	fgetcsv(handle)	"Jane,Smith,25"	Array('Jane', 'Smith', '25') printed
4	Read third line	fgetcsv(handle)	"Bob,Brown,40"	Array('Bob', 'Brown', '40') printed
5	Read next line	fgetcsv(handle)	EOF reached	false returned, loop ends
6	Close file	fclose(handle)	File closed	No output
7	Open file for writing	fopen('output.csv', 'w')	File opened	Resource handle assigned
8	Write first line	fputcsv(handle, ['Name', 'Age'])	Writes "Name,Age\n"	1 (success) returned
9	Write second line	fputcsv(handle, ['Alice', '28'])	Writes "Alice,28\n"	1 (success) returned
10	Close file	fclose(handle)	File closed	No output

💡 Reading stops when fgetcsv returns false at EOF; writing stops after all lines written and file closed.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 8	After Step 9	Final
handle	null	resource	resource	resource	resource	null	resource	resource	null
data	null	['John', 'Doe', '30']	['Jane', 'Smith', '25']	['Bob', 'Brown', '40']	false	false	null	null	null

Key Moments - 3 Insights

Why does the loop stop reading the CSV file?

The loop stops because fgetcsv returns false when it reaches the end of the file, as shown in step 5 of the execution_table.

What does fputcsv return after writing a line?

fputcsv returns 1 on success after writing a line, as seen in steps 8 and 9 of the execution_table.

Why do we need to close the file after reading or writing?

Closing the file releases system resources and ensures data is saved properly, shown in steps 6 and 10 where fclose is called.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'data' after step 3?

A ['Jane', 'Smith', '25']

B ['John', 'Doe', '30']

C false

D null

💡 Hint

Check the 'data' column in the variable_tracker after step 3.

At which step does reading from the CSV file stop?

A Step 4

B Step 5

C Step 6

D Step 7

💡 Hint

Look at the execution_table where fgetcsv returns false indicating EOF.

If we forget to call fclose after writing, what might happen?

A Data might not be saved properly

B File will be deleted automatically

C Reading will stop early

D Nothing, fclose is optional

💡 Hint

Refer to key_moments about why closing files is important.

Concept Snapshot

CSV file reading and writing in PHP:
- Use fopen() to open file ('r' for read, 'w' for write)
- Use fgetcsv() to read CSV lines as arrays
- Use fputcsv() to write arrays as CSV lines
- Loop reading until fgetcsv returns false (EOF)
- Always fclose() to close the file and save resources

Full Transcript

This visual execution trace shows how to read and write CSV files in PHP. First, fopen opens the file for reading. Then, a while loop uses fgetcsv to read each line as an array until it returns false at the end of the file. Each array is printed. After reading, fclose closes the file. For writing, fopen opens the file in write mode. fputcsv writes arrays as CSV lines. After writing all lines, fclose closes the file. Variables like 'handle' track the file resource, and 'data' holds the current CSV row. Closing files is important to save data and free resources.