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How to: Open and Append to a Log File

StreamWriter and StreamReader write characters to and read characters from streams. The following code example opens the log.txt file for input, or creates the file if it does not already exist, and appends information to the end of the file. The contents of the file are then written to standard output for display. As an alternative to this example, the information could be stored as a single string or string array, and the WriteAllText or WriteAllLines method could be used to achieve the same functionality.

NoteNote

Visual Basic users may choose to use the methods and properties provided by the Log class or FileSystem class for creating or writing to log files.


using namespace System;
using namespace System::IO;

ref class DirAppend
{
public:
    static void Main()
    {
        StreamWriter^ w = File::AppendText("log.txt");
        Log("Test1", w);
        Log("Test2", w);
        // Close the writer and underlying file.
        w->Close();
        // Open and read the file.
        StreamReader^ r = File::OpenText("log.txt");
        DumpLog(r);
        r->Close();
    }

    static void Log(String^ logMessage, TextWriter^ w)
    {
        w->Write("\r\nLog Entry : ");
        w->WriteLine("{0} {1}", DateTime::Now.ToLongTimeString(),
            DateTime::Now.ToLongDateString());
        w->WriteLine("  :");
        w->WriteLine("  :{0}", logMessage);
        w->WriteLine ("-------------------------------");
        // Update the underlying file.
        w->Flush();
    }

    static void DumpLog(StreamReader^ r)
    {
        // While not at the end of the file, read and write lines.
        String^ line;
        while ((line = r->ReadLine()) != nullptr)
        {
            Console::WriteLine(line);
        }
        r->Close();
    }
};

int main()
{
    DirAppend::Main();
}


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