What is a good way to loop through each line of a multiline string without using much more memory (for example without splitting it into an array)?
I suggest using a combination of StringReader
and my LineReader
class, which is part of MiscUtil but also available in this StackOverflow answer - you can easily copy just that class into your own utility project. You'd use it like this:
string text = @"First line
second line
third line";
foreach (string line in new LineReader(() => new StringReader(text)))
{
Console.WriteLine(line);
}
Looping over all the lines in a body of string data (whether that's a file or whatever) is so common that it shouldn't require the calling code to be testing for null etc :) Having said that, if you do want to do a manual loop, this is the form that I typically prefer over Fredrik's:
using (StringReader reader = new StringReader(input))
{
string line;
while ((line = reader.ReadLine()) != null)
{
// Do something with the line
}
}
This way you only have to test for nullity once, and you don't have to think about a do/while loop either (which for some reason always takes me more effort to read than a straight while loop).
You can use a StringReader
to read a line at a time:
using (StringReader reader = new StringReader(input))
{
string line = string.Empty;
do
{
line = reader.ReadLine();
if (line != null)
{
// do something with the line
}
} while (line != null);
}
from MSDN for StringReader
string textReaderText = "TextReader is the abstract base " +
"class of StreamReader and StringReader, which read " +
"characters from streams and strings, respectively.\n\n" +
"Create an instance of TextReader to open a text file " +
"for reading a specified range of characters, or to " +
"create a reader based on an existing stream.\n\n" +
"You can also use an instance of TextReader to read " +
"text from a custom backing store using the same " +
"APIs you would use for a string or a stream.\n\n";
Console.WriteLine("Original text:\n\n{0}", textReaderText);
// From textReaderText, create a continuous paragraph
// with two spaces between each sentence.
string aLine, aParagraph = null;
StringReader strReader = new StringReader(textReaderText);
while(true)
{
aLine = strReader.ReadLine();
if(aLine != null)
{
aParagraph = aParagraph + aLine + " ";
}
else
{
aParagraph = aParagraph + "\n";
break;
}
}
Console.WriteLine("Modified text:\n\n{0}", aParagraph);
I know this has been answered, but I'd like to add my own answer:
using (var reader = new StringReader(multiLineString))
{
for (string line = reader.ReadLine(); line != null; line = reader.ReadLine())
{
// Do something with the line
}
}
Here's a quick code snippet that will find the first non-empty line in a string:
string line1;
while (
((line1 = sr.ReadLine()) != null) &&
((line1 = line1.Trim()).Length == 0)
)
{ /* Do nothing - just trying to find first non-empty line*/ }
if(line1 == null){ /* Error - no non-empty lines in string */ }
To update this ancient question for .NET 4, there is now a much neater way:
var lines = File.ReadAllLines(filename);
foreach (string line in lines)
{
Console.WriteLine(line);
}
来源:https://stackoverflow.com/questions/1500194/c-looping-through-lines-of-multiline-string