View Category
Files
Reading

Read the contents of a file into a string

ruby
file = File.new("Solution108.rb")
whole_file = file.read
csharp
string contents = System.IO.File.ReadAllText("filename.txt");
cpp
IO::FileStream^ file; String^ buffer;

try
{
file = gcnew IO::FileStream("test.txt", IO::FileMode::Open);
buffer = gcnew String((gcnew IO::BinaryReader(file))->ReadChars(file->Length));
}
IO::StreamReader^ stream; String^ buffer;

try
{
stream = gcnew IO::StreamReader("test.txt");
buffer = stream->ReadToEnd();
}
String^ buffer = IO::File::ReadAllText("test.txt");
clojure
(slurp "/tmp/foobar")

Process a file one line at a time

Open the source file to your solution and print each line in the file, prefixed by the line number, like:
1> First line of file
2> Second line of file
3> Third line of file
ruby
File.open("Solution103.rb").each_with_index { |line, count|
puts "#{count} > #{line}
}
csharp
int counter = 0;

// If the file is large, you would want to buffer this instead of reading everything at once
foreach (string line in System.IO.File.ReadAllLines("filename.txt"))
{
Console.WriteLine("{0}> {1}", ++counter, line);
}
cpp
IO::StreamReader^ stream; String^ ln; int i = 0;

try
{
stream = gcnew IO::StreamReader("test.txt");
while ((ln = stream->ReadLine())) Console::WriteLine("{0}> {1}", ++i, ln);
}
int i = 0;
for each(String^ line in IO::File::ReadAllLines("test.txt")) Console::WriteLine("{0}> {1}", ++i, line);
clojure
(defn read-line-by-line [fn]
(reduce str (map (partial format "%d> %s\n")
(iterate inc 1)
(read-lines fn))))
Writing

Write a string to a file

ruby
File.new("a_file", "w") << "some text"
csharp
System.IO.File.WriteAllText("filename.txt", "Some text to write to the file");
cpp
IO::StreamWriter^ stream;

try
{
stream = gcnew IO::StreamWriter("test.txt", false);
stream->WriteLine("This line overwites file contents!");
}
clojure
(with-out-writer "output.txt" (println "Hello file!"))

Append to a file

ruby
file = File.new('/tmp/test.txt', 'a+') ; file.puts 'This line appended to file!!' ; file.close()
csharp
System.IO.File.AppendAllText("filename.txt", "Some text to append to the file");
cpp
IO::StreamWriter^ stream;

try
{
stream = gcnew IO::StreamWriter("test.txt", true);
stream->WriteLine("This line appended to file!");
}
clojure
(with-out-append-writer "output.txt" (println "This is appended to the file"))
Directories

Process each file in a directory

ruby
directory = '/tmp' ; Dir.foreach(directory) {|file| puts "#{file}"}
csharp
foreach (string filename in System.IO.Directory.GetFiles(directory)) ProcessFile(filename);
cpp
for each(String^ filename in IO::Directory::GetFiles(dirname)) process(filename);
clojure
; (defn process-file [f] "process one file" body...)
(map process-file (.listFiles (File. ".")))

Process each file in a directory recursively

ruby
def procdir(dirname)
Dir.foreach(dirname) do |dir|
dirpath = dirname + '/' + dir
if File.directory?(dirpath) then
if dir != '.' && dir != '..' then
puts "DIRECTORY: #{dirpath}" ; procdir(dirpath)
end
else
puts "FILE: #{dirpath}"
end
end
end

# ------

procdir('/tmp')
cpp
void processFile(String^ filename) { Console::WriteLine("{0}", filename); }

void processDirectory(String^ dirname)
{
for each(String^ filename in IO::Directory::GetFiles(dirname)) processFile(filename);
for each(String^ subdirname in IO::Directory::GetDirectories(dirname)) processDirectory(subdirname);
}

int main()
{
processDirectory("c:\\");
}
clojure
; (defn process-file [f] "process one file" body...)
(map process-file (file-seq (File. ".")))