从文件中读取部分内容的正确方法是什么?

本文关键字：方法是什么文件读取部 | 更新日期: 2023-09-27 18:18:42

我想从一个文本文件中读取部分内容，该文件有以下内容和换行符:

Content-Type: multipart/signed;
    boundary="boundarytext"
--<boundarytext>
Content-Type: text/plain
{1:A}{2:B      N}{4:
:10:C123
:11:124
:43E:
test.txt
2010-03-20/09:37:45
Accepted
-}
--<boundarytext>

我期待以下内容:

{1:A}{2:B      N}{4:
:10:C123
:11:124
:43E:
test.txt
2010-03-20/09:37:45
Accepted
-}

当前正在逐行读取文件。

是否有最好的方法来达到我的预期结果?

这是我使用的代码，

    using (var fileRead = new StreamReader(@"c:'temp'testfile.txt"))
    {
        var blockIdentifier = "{1:";
        var textBlockIdentifier = "-}";
        var fileContent = fileRead.ReadToEnd();
        var startPos = fileContent.LastIndexOf(blockIdentifier);
        var length = (fileContent.IndexOf(textBlockIdentifier) + 2) - startPos;
        var newContent = fileContent.Substring(startPos, length);
    }

谢谢

从文件中读取部分内容的正确方法是什么?

你可以使用LINQ:

string[] relevantLines = File.ReadLines(path)
    .SkipWhile(l => !l.StartsWith("--<boundarytext>"))
    .Skip(3)
    .TakeWhile(l => !l.StartsWith("--<boundarytext>"))
    .ToArray();

似乎boundarytext总是在变化，所以你需要先检测它:

string boundaryTextLine = File.ReadLines(path)
  .FirstOrDefault(l => l.IndexOf("boundary=", StringComparison.InvariantCultureIgnoreCase) >= 0);
if(boundaryTextLine != null)
{
    string boundaryText = boundaryTextLine
        .Substring(boundaryTextLine.IndexOf("boundary=", StringComparison.InvariantCultureIgnoreCase) + "boundary=".Length)
        .Trim(' ', '"');
}

我个人会使用正则表达式

/(?<='-'-<boundarytext>)'n(.+)'n(?='-'-<boundarytext>)/gsU

见:https://regex101.com/r/rB1tC8/1

我甚至会解析消息中的content_type。为方便起见，这里有一个c#

的工作测试用例

        [TestMethod]
        public void TestMethod1()
        {
            var input = @"Content-Type: multipart/signed;
    boundary='boundarytext1'
--<boundarytext1>
Content-Type: text/plain
{1:A}{2:B      N}{4:
:10:C123
:11:124
:43E:
test.txt
2010-03-20/09:37:45
Accepted
-}
--<boundarytext1>
Content-Type: multipart/signed;
    boundary='boundarytext2'
--<boundarytext2>
Content-Type: text/plain
{1:A}{2:B      N}{4:
:10:C123
:11:124
:43E:
test.txt
2010-03-20/09:37:45
Accepted
-}
--<boundarytext2>".Replace("'", "'"");
            var pattern = @"
boundary='(.+)'         # capture the boundary delimiter in '1
.+
(--<'1>)                # every message starts with --<boundary>
.+
Content-Type:'s
(?<content_type>['w/]+) # capture the content_type
('r?'n)+
(?<content>.+?)         # capture the content
('r?'n)+
(--<'1>)                # every message ends with --<boundary>
".Replace("'", "'"");
            var regex = new Regex(pattern, 
                RegexOptions.Singleline | RegexOptions.IgnorePatternWhitespace);
            var matches = regex.Matches(input);
            Assert.AreEqual(2, matches.Count);
            foreach (Match match in matches)
            {
                var content_type = match.Groups["content_type"].Value;
                var content = match.Groups["content"].Value;
                Assert.AreEqual("text/plain", content_type);
                Assert.IsTrue(content.StartsWith("{1") && content.EndsWith("-}"));
            }
        }
    }

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