Thread: simple File I/O question

  1. #1
    Registered User
    Join Date
    Aug 2003

    simple File I/O question


    Below is a piece of code that opens a file.
    if I got readFile(fileName) where "fileName" is a string containing a file the program does not compile.

    string fileName;
    fileName = "blah.txt";
    ifstream readFile;;
    ifstream readFile;"blah.txt");
    if I enter the file name directly in quotes it works. How do I specify the file I want to open using a variable?

    I've of course #include 'ed string and fstream

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    Try fileName.c_str() );
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Registered User
    Join Date
    Aug 2003
    thanks, just found out myself, learn the whole s string part and was a about to reply that I found a solution!

    Good to see I was on the right track

  4. #4
    Registered User
    Join Date
    Oct 2003
    Code: fileName.c_str() );
    what does the .c_str() do?

  5. #5
    Registered User PotitKing's Avatar
    Join Date
    Dec 2001


    The c_str() and data() methods of the string class, returns the string as an array of bytes, like "old" C strings.

    string s = "Hello";
    char *oldtypestring = s.c_str();

    oldtypestring is now "Hello\0"
    % gcc -v
    Configured with: FreeBSD/i386 system compiler
    Thread model: posix
    gcc version 3.3.3 [FreeBSD] 20031106

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