Simple ifstream Question

This is a discussion on Simple ifstream Question within the C++ Programming forums, part of the General Programming Boards category; Can you use the same ifstream on multiple files? Example: ifstream input_file( "file.txt" ); input_file.close(); ifstream input_file( "file2.txt" ); This ...

  1. #1
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    Simple ifstream Question

    Can you use the same ifstream on multiple files?

    Example:

    ifstream input_file( "file.txt" );
    input_file.close();
    ifstream input_file( "file2.txt" );

    This gives an error.

    Is there any way to make it work?

  2. #2
    Registered User Codeplug's Avatar
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    You should call clear() as well after close().

    gg

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    You can't declare two variables of the same name in the same scope. So the second one would just need to be an open call, not a constructor.

  4. #4
    The larch
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    But there probably isn't much reason to go through all the trouble of reusing the fstream.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  5. #5
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    Quote Originally Posted by Codeplug View Post
    You should call clear() as well after close().

    gg
    Quote Originally Posted by tabstop View Post
    You can't declare two variables of the same name in the same scope. So the second one would just need to be an open call, not a constructor.
    Yeah woops, I mistyped. Here's what I have now:

    Code:
    ifstream input_file( "file.txt" );
    input_file.close();
    input_file.clear();
    
    input_file( "file2.txt" ); // Line 57
    But still,

    Code:
    ex2.cpp:57: error: expected `;' before ‘open’
    ex2.cpp:57: warning: statement has no effect
    Quote Originally Posted by anon View Post
    But there probably isn't much reason to go through all the trouble of reusing the fstream.
    I have to open about 20 files and do various things in each. Is there a way do reuse the same ifstream, or do I have to make 20 different ifstream variables?

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Paul22000 View Post
    Yeah woops, I mistyped. Here's what I have now:

    Code:
    ifstream input_file( "file.txt" );
    input_file.close();
    input_file.clear();
    
    input_file( "file2.txt" ); // Line 57
    But still,

    Code:
    ex2.cpp:57: error: expected `;' before ‘open’
    ex2.cpp:57: warning: statement has no effect


    I have to open about 20 files and do various things in each. Is there a way do reuse the same ifstream, or do I have to make 20 different ifstream variables?
    I don't see the word "open" in that last line. Why don't I?

  7. #7
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    Quote Originally Posted by tabstop View Post
    I don't see the word "open" in that last line. Why don't I?
    Woops

    I did

    Code:
    ifstream input_file( "file.txt" );
    input_file.close();
    input_file.clear();
    
    input_file open( "file2.txt" );

  8. #8
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Paul22000 View Post
    Woops

    I did

    Code:
    ifstream input_file( "file.txt" );
    input_file.close();
    input_file.clear();
    
    input_file open( "file2.txt" );
    Is that a direct copy-paste from the file? (If not, why not?) You need a dot between file and open.

  9. #9
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    Quote Originally Posted by tabstop View Post
    You need a dot between file and open.
    AH!!!!!!!!!!!!!!!!!!!!!

    Lol

    Thank you, works now

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