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C++ file i/o

  1. Apr 18, 2012 #1
    I felt like learning a bit about file input and output in C++. Tried some code, couldn't get it to work unless I made the path to the file a string literal, not a variable type. Why is this, and is there any way to get a string data type to be inputted as a path?
  2. jcsd
  3. Apr 18, 2012 #2


    Staff: Mentor

    You should be able to do it with the path stored in a variable. Show us the code you're talking about.
  4. Apr 18, 2012 #3

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    I'm assuming you tried something like:
    Code (Text):
    std::string filename("/path/to/file");
    std::ifstream ifs(filename);
    Did you?

    If so, try:
    Code (Text):
    std::string filename("/path/to/file");
    std::ifstream ifs(filename.c_str());
  5. Apr 18, 2012 #4
    I tried

    Code (Text):
    #include <iostream>
    #include <fstream>
    #include <string>
    using namespace std;

    int main()
        string file = "Documents/Programming/C++.txt";
        string contents;
        ifstream in;
        ofstream out;
        out << "This is a C++ program here." << endl;
        cout << contents << endl;
        return 0;
    Note that I'm on a MAC, so that is a valid path. Using file.c_str seemed to work, thanks!
  6. Apr 18, 2012 #5

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    You're welcome. :smile:
  7. Apr 18, 2012 #6


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    Staff: Mentor

    You'd think that the C++ ifstream constructor could take a C++ string as its argument. My understanding is that it's a backward-compatibility issue with ancient versions of C++ that pre-date the first standardized version (in which the 'string' data type was introduced).
  8. Apr 18, 2012 #7


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    You'd still think you could create another constructor that takes a string object; I don't see how any backwards compatibility issues would occur.
  9. Apr 19, 2012 #8

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    You'd think they would have fixed this in C++03, but they didn't.
    I wonder why, since they must have discussed this.

    Anyway, apparently it is finally fixed in C++11.
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