Chris K. Chris K. - 1 year ago 84
C# Question

Slow String Formatting in C# when using more than a few lines

I have created a process which reads a "template" text file and then based on the String.Format requirements uses the tokens to place my custom text in.

So, everything works, but the process is slow.

The template file can have about 500-1000 lines; I am looking for a way to speed this process up.

Any ideas?

Here is my code below:

templateFilePath = System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase).Replace("file:\\", "");
templateFilePath += "\\Templates\\TemplateFile.txt";
tempRequestFilePath = System.IO.Path.GetTempPath();
tempRequestFilePath += Guid.NewGuid();
responseFileToWrite = tempRequestFilePath + "\\" + Path.GetFileNameWithoutExtension(zipMergeFilePath) + ".RSP";
if (!File.Exists(templateFilePath))
return false;
templateString = System.IO.File.ReadAllText(templateFilePath);
currentRecordNumber = 1;
for (int i = 0; i < createToProcess.rtfText.Lines.Length; i++)
if (createToProcess.rtfText.Lines[i].Contains("TAG ID:"))
string currentTagID = createToProcess.rtfText.Lines[i].Substring(9, 11).Trim();
string currentCustomerNumber = createToProcess.rtfText.Lines[i].Substring(25, 12).Trim();
string currentTaxPeriod = createToProcess.rtfText.Lines[i].Substring(42, 8).Trim();
string currentCustomerPhoneNumber = createToProcess.rtfText.Lines[i].Substring(55, 9).Trim();
DateTime datePurchases = (DateTime.Now).AddDays(-7);
DateTime dateReceived = (DateTime.Now).AddYears(10);
DateTime dateModified = (DateTime.Now).AddYears(-1);
string currentResearchCreateRecord = String.Format(templateString,
datePurchases.Month.ToString("00") + datePurchases.Day.ToString("00") + datePurchases.Year.ToString("0000"),
"RecordNo: " + currentRecordNumber.ToString(),
dateReceived.Month.ToString("00") + dateReceived.Day.ToString("00") + dateReceived.Year.ToString("0000"),
dateModified.Month.ToString("00") + dateModified.Day.ToString("00") + dateModified.Year.ToString("0000")
File.AppendAllText(responseFileToWrite, currentResearchCreateRecord);
currentRecordNumber += 1;
using (ZipFile currentZipFile = new ZipFile())
currentZipFile.AddFile(responseFileToWrite, "");
return true;

Answer Source

You're re-opening the file handle for each line. That's an expensive operation, and slows you down.

Instead, create (in a using block) a StreamWriter for the file, and call WriteLine() to write a single line without closing the file.

Also, reading the Lines property is quite slow. Change that to a foreach loop (or just cache the array) instead of rerunning all that code for each line.

Finally, don't call DoEvents().

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