c# - C#：循环遍历多行字符串

Question

什么是循环遍历多行字符串的每一行而不使用更多内存（例如不将其拆分为数组）的好方法？

Answer 1

我建议使用StringReader和我的LineReader类的组合，它是MiscUtil的一部分，但也可在这个 StackOverflow 答案中找到- 您可以轻松地将该类复制到您自己的实用程序项目中。你会这样使用它：

string text = @"First line
second line
third line";

foreach (string line in new LineReader(() => new StringReader(text)))
{
    Console.WriteLine(line);
}

循环遍历字符串数据主体中的所有行（无论是文件还是其他）是如此普遍，以至于它不应该要求调用代码测试 null 等:) 话虽如此，如果你确实想做一个手动循环，这是我通常比 Fredrik 更喜欢的形式：

using (StringReader reader = new StringReader(input))
{
    string line;
    while ((line = reader.ReadLine()) != null)
    {
        // Do something with the line
    }
}

这样，您只需测试一次无效性，并且您也不必考虑 do/while 循环（由于某种原因，这总是比直接的 while 循环花费我更多的精力阅读）。

Answer 2

您可以使用 a 一次StringReader读取一行：

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);
}

Answer 3

我知道这已经得到解答，但我想添加我自己的答案：

using (var reader = new StringReader(multiLineString))
{
    for (string line = reader.ReadLine(); line != null; line = reader.ReadLine())
    {
        // Do something with the line
    }
}

Answer 4

来自 MSDN 的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);

Answer 5

这是一个快速代码片段，它将在字符串中找到第一个非空行：

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 */ }

Answer 6

尝试使用 String.Split 方法：

string text = @"First line
second line
third line";

foreach (string line in text.Split('\n'))
{
    // do something
}

Answer 7

有时我认为我们可以使解决方案过于复杂，以避免重复一行代码。这就是我首先提出这个问题的原因。

经过一番思考，我得出结论，最简单的解决方案是重复ReadLine循环之前和内部。

using (var stringReader = new StringReader(input))
{
    var line = await stringReader.ReadLineAsync();

    while (line != null)
    {
        // do something
        line = await stringReader.ReadLineAsync();
    }
}

我意识到这可能被认为不遵循 DRY 原则，但考虑到简单性，我认为值得考虑。