std.stdio.file.readln - multiple declarations

This can be faster than line = File.readln() because you can reuse the buffer for each call. Note that reusing the buffer means that you must copy the previous contents if you wish to retain them.

Prototypes

size_t readln(C)(
  C[] buf,
  dchar terminator = '\x0a'
)
if (isSomeChar!C && is(Unqual!C == C) && !is(C == enum));

size_t readln(C, R)(
  C[] buf,
  R terminator
)
if (isSomeChar!C && is(Unqual!C == C) && !is(C == enum) && isBidirectionalRange!R && is(typeof(terminator.front == (dchar).init)));

Parameters

Returns

0 for end of file, otherwise number of characters read

Throws

StdioException on I/O error, or UnicodeException on Unicode conversion error.

Example

// Read lines from stdin into a string
// Ignore lines starting with '#'
// Write the string to stdout

void main()
{
    string output;
    char[] buf;

    while (stdin.readln(buf))
    {
        if (buf[0] == '#')
            continue;

        output ~= buf;
    }

    write(output);
}

This method can be more efficient than the one in the previous example because stdin.readln(buf) reuses (if possible) memory allocated for buf, whereas line = stdin.readln() makes a new memory allocation for every line.

For even better performance you can help readln by passing in a large buffer to avoid memory reallocations. This can be done by reusing the largest buffer returned by readln:

Example

// Read lines from stdin and count words

void main()
{
    char[] buf;
    size_t words = 0;

    while (!stdin.eof)
    {
        char[] line = buf;
        stdin.readln(line);
        if (line.length > buf.length)
            buf = line;

        words += line.split.length;
    }

    writeln(words);
}

This is actually what byLine does internally, so its usage is recommended if you want to process a complete file.

This version manages its own read buffer, which means one memory allocation per call. If you are not retaining a reference to the read data, consider the File.readln(buf) version, which may offer better performance as it can reuse its read buffer.

Prototype

S readln(S)(
  dchar terminator = '\x0a'
)
if (isSomeString!S);

Parameters

Note

String terminators are not supported due to ambiguity with readln(buf) below.

Returns

The line that was read, including the line terminator character.

Throws

StdioException on I/O error, or UnicodeException on Unicode conversion error.

Example

// Reads stdin and writes it to stdout.
import std.stdio;

void main()
{
    string line;
    while ((line = stdin.readln()) !is null)
        write(line);
}