saving to a file

This is a discussion on saving to a file within the C++ Programming forums, part of the General Programming Boards category; Hey guys is there a way i could inform the user if a txt file already exists when they enter ...

  1. #1
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    saving to a file

    Hey guys is there a way i could inform the user if a txt file already exists when they enter the file name e.g. c:\\hi.txt so it won't get over written in my program the saved results are handeled by the following:

    Code:
    	cin.getline(file, 100); 
    
    	system("cls"); 
    
    
    	ofstream f;
    	f.open(file);

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    Open the file for reading. If that fails, the file doesn't exist.

    This doesn't work all the time, but it's better than just clobbering the file.
    dwk

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    Code:
    if ( file.is_open() ) {
            std::cout<<"File already exists"<<endl;
    }
    Is that the sort of thing you are meaning?

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    I was able to solve the problem using the ios:noreplace and it returns fail if there is a problem, is this a good way to do it?

    Thanks.

  5. #5
    Devil's Advocate SlyMaelstrom's Avatar
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    No, ios::noreplace isn't standard. You can use this, instead:

    Code:
    fstream myFile(filename, ios_base::in); // Open for reading
    if (!myFile) {   // If it doesn't exist, then good
       myFile.open(filename, ios_base::out); // Open for writing
    }
    else {
       cout << "File already exists. Overwrite?";
       // ... and so on
    }
    Last edited by SlyMaelstrom; 03-25-2006 at 12:00 PM.
    Sent from my iPadŽ

  6. #6
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    Hi, thanks for the reply but what do you mean by not standard? Thanks again

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    C++ experts got together and made a document called the C++ standard that defines the language and its rules so that people could write code that would work on different compilers and different operating systems. Something that is non-standard might work on one compiler or one platform, but not on another.

    In this case, ios::no_replace won't work on many modern compilers. For example, it might work with <fstream.h> in VC++ version 6, but when you move to version 7 or 8 and try to compile it, it won't compile (those require the standard header <fstream>). Also, some people trying to help on this forum and others won't be able to compile the code if you use non-standard or outdated code.

    If it works for you and you have no need for it to work in the future or for anyone else, then it is not that bad to use the non-standard <fstream.h> code, but since there is a perfectly valid alternative that won't come with all the other hassles it is probably a better idea to use it.

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