File.ReadLines() vs. File.ReadAllLines(): Which Method Offers Better Performance for Reading Files?

Performance difference between File.ReadLines() and File.ReadAllLines() in System.IO

File.ReadLines() and File.ReadAllLines() are both methods in the System.IO namespace and are used to read file data into a string array. However, they differ in performance and usage.

File.ReadAllLines()

File.ReadAllLines() Read the entire file into memory at once and store it as an array. This method is more efficient for smaller files because faster processing is achieved. However, with large files, this can cause performance issues since the entire file must be loaded into memory before any processing can occur.

File.ReadLines()

File.ReadLines() returns a IEnumerable<string>, which is a way to lazy load the contents of the file. Instead of loading the entire file into memory, it reads the file line by line, returning each line as needed. For large files, this approach is preferable because it avoids the need to load the entire file into memory.

Summary of performance differences

The following table summarizes the performance differences between File.ReadLines() and File.ReadAllLines():

方法	性能	内存使用
File.ReadLines()	大型文件更佳	更低
File.ReadAllLines()	小型文件更佳	更高

Examples of usage

Here's how to use File.ReadLines() to read a file line by line:

foreach (var line in File.ReadLines("C:\mytxt.txt"))
{
    // 处理每一行...
}

On the other hand, use File.ReadAllLines() to load the entire file into memory as an array:

string[] lines = File.ReadAllLines("C:\mytxt.txt");

Conclusion

For large files, it is generally recommended to use File.ReadLines() as it uses a lazy loading mechanism. For small files, either method can be used, depending on the specific requirements of the application.

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