What are the differences and advantages and disadvantages between md5_file() and file_get_contents() functions when reading files?

In PHP, reading file content is a very common operation. The md5_file() function and the file_get_contents() function are both common functions for processing files, but their uses and performance differences are significant. This article will analyze in detail the differences and advantages and disadvantages of these two functions when reading files, and help you choose the right function to complete different tasks.

1. Function introduction

• md5_file(string $filename): string|false
  This function directly calculates the MD5 hash value of the specified file and returns a 32-bit string representing the MD5 digest of the file. If the file read fails, false is returned.

• file_get_contents(string $filename, bool $use_include_path = false, resource $context = null, int $offset = 0, int $maxlen = null): string|false
  This function reads the entire file content into a string and returns it. If the read fails, false is returned.

2. Purpose and results of use

• md5_file()
  The main purpose is to calculate the MD5 value of the file, which is used to verify the integrity of the file, verify whether the file has been tampered with or as a unique identifier of the file. It does not return the contents of the file, but rather the summary of the contents of the file.

• file_get_contents()
  Used to read all the contents of the file to facilitate subsequent processing of file text or binary data. What is returned is the entire data string of the file.

3. Performance comparison

• The implementation of md5_file() is usually a built-in optimization operation, which directly hash the file content, and does not need to load all files into memory as string processing, which is more efficient and has less memory usage.

• file_get_contents() will read the entire file content into memory at one time. For larger files, it may lead to higher memory usage. If you only need to verify file consistency in the future, this is unnecessary waste.

4. Applicable scenarios

5. Sample code comparison

Use md5_file() to calculate the MD5 value of a file

 <?php
$file = 'http://m66.net/path/to/file.txt';

$md5 = md5_file($file);
if ($md5 === false) {
    echo "Failed to read the file";
} else {
    echo "FiledMD5The value is: " . $md5;
}
?>

Use file_get_contents() to read file content

 <?php
$file = 'http://m66.net/path/to/file.txt';

$content = file_get_contents($file);
if ($content === false) {
    echo "Failed to read the file";
} else {
    echo "The file content is as follows：\n";
    echo $content;
}
?>

6. Summary

• If your goal is to quickly get the MD5 check value of a file, md5_file() is a better choice , which is more efficient and memory-saving.

• If you need to perform further operations on the file content, such as parsing text, modifying data, etc., file_get_contents() can help you read the complete content .

• For large files, it is recommended to avoid using file_get_contents() to directly read all content at one time. You can consider reading in chunks or using stream operations.

Understanding the differences and advantages and disadvantages of these two functions can more reasonably design program logic and improve program performance and stability.

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