Using fstream to open a file that is created only during runtime
CodeGuru Home VC++ / MFC / C++ .NET / C# Visual Basic VB Forums Developer.com
Results 1 to 5 of 5

Thread: Using fstream to open a file that is created only during runtime

Threaded View

  1. #1
    Join Date
    Nov 2009
    Posts
    6

    Using fstream to open a file that is created only during runtime

    Hi,

    I'm using Visual C++ 6.0 and I'm trying to use fstream to open and read a file that is created only during runtime. This file is written by another function running on another thread, and my program will keep trying to "open" the file until it can be opened, i.e. after it's created, then read 3 numbers from it and execute the rest of its code.

    The file test.txt has the content

    Code:
    1
    3
    4
    My program that polls and opens the file is as follows:

    Code:
    ifstream fin;
    std::string tfile, snum1, snum2, snum3;
    long int num2, num3;
        
    tfile.assign(argv[1]);
    printf("Begin prog %s\n", tfile.c_str());
        
    fp: fin.open(donefile.c_str(), ifstream::in);
    if (fin.is_open())
    {
       printf("fin is open\n");
       getline(fin, snum1);
       getline(fin, snum2);
       getline(fin, snum3);
       num2 = atol(snum2.c_str());
       num3 = atol(snum3.c_str());
       printf("snum1 = %s\n", snum1.c_str());
       printf("num2 = %d num3 = %d\n", num2, num3);
       fin.close();
    }
    else
    {
       printf("Cannot open file %s\n", tfile.c_str());
       fin.close();
       Sleep(500);
       goto fp;
    }
        
    remove(tfile.c_str());
    printf("End of prog\n");
    I executed the program by

    Code:
    test_prog.exe "C:\test.txt"
    and waited about 3 seconds before putting the test.txt file into C:\

    My output was

    Code:
    Begin prog C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    fin is open
    snum1 = 
    num2 = 0 num3 = 0
    End of prog
    The test.txt file disappears after I refresh the C:\ folder.

    So the values for snum1, num2 and num3 are all wrong, as if the file was not read correctly.

    If I put a while fin.good() loop after printf("fin is open\n"); for that entire block (until printing the values of num2 and num3), then I get

    Code:
    Begin prog C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    Cannot open file C:\test.txt
    fin is open
    End of prog
    How can I correctly read a file that is only created during runtime?

    Thank you.
    Last edited by hjazz; November 20th, 2012 at 05:28 AM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


Windows Mobile Development Center


Click Here to Expand Forum to Full Width

This is a CodeGuru survey question.


Featured


HTML5 Development Center