file io

Steven Schveighoffer schveiguy at gmail.com
Thu Sep 6 18:37:49 UTC 2018


On 9/6/18 2:30 PM, Steven Schveighoffer wrote:
> On 9/6/18 1:07 PM, rikki cattermole wrote:
>> On 07/09/2018 4:17 AM, Arun Chandrasekaran wrote:
>>> On Thursday, 6 September 2018 at 16:13:42 UTC, hridyansh thakur wrote:
>>>> how to read a file line by line in D
>>>
>>> std.stdio.File.byLine()
>>>
>>> Refer the doc here: 
>>> https://dlang.org/library/std/stdio/file.by_line.html
>>>
>>> An example from the doc:
>>>
>>> ```
>>> import std.algorithm, std.stdio, std.string;
>>> // Count words in a file using ranges.
>>> void main()
>>> {
>>>      auto file = File("file.txt"); // Open for reading
>>>      const wordCount = file.byLine()            // Read lines
>>>                            .map!split           // Split into words
>>>                            .map!(a => a.length) // Count words per line
>>>                            .sum();              // Total word count
>>>      writeln(wordCount);
>>> }
>>> ```
>>
>> Ranges will be far too advanced of a topic to bring up at this stage.
>>
>> So something a little more conventional might be a better option:
>>
>> ---
>> import std.file : readText;
>> import std.array : split;
>> import std.string : strip;
>>
>> string text = readText("file.txt");
>> string[] onlyWords = text.split(" ");
>>
>> uint countWords;
>> foreach(ref word; onlyWords) {
>>      word = word.strip();
>>      if (word.length > 0)
>>          countWords++;
>> }
>> ---
> 
> Ugh, don't do that, it will read the unknown-length file into RAM all at 
> once.
> 
> foreach(word; File("file.txt").byLine)
> {
>     word = word.strip();
>     if(word.length > 0) countWords++;
> }
> 
> That will buffer one line at a time and achieve the same results.

ugh, I didn't think this through. This works:

foreach(line; File("file.txt").byLine)
{
    foreach(word; line.split(" "))
    {
    	word = word.strip();
    	if(word.length > 0) countWords++;
    }
}

-Steve


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