String parameter errors

This is a discussion on String parameter errors within the C++ Programming forums, part of the General Programming Boards category; I'm trying to make a program that checks if a file is there, if not make it with some writting ...

  1. #1
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    String parameter errors

    I'm trying to make a program that checks if a file is there, if not make it with some writting in it. I've done my best make sure everything is correct.

    Code:
    Code:
    /* Section: header */
    #include <iostream>
    #include <fstream>
    #include <cstdlib>
    #include <string>
    
    /* Section: constant */
    const std::string NEWLINE = "\n"
    const std::string NEWLINE_FLUSH = "std::endl"
    
    /* Section: prototype */
    void nfound( const std::string &v_file );
    
    int main( int argc, char *argv[] ) {
      using namespace std;
      string the_file = "test_file.txt";
      if ( "the_file" ) {
        cout << "File found!";
      } else {
        cout << "File not found!";
        nfound( "the_file" );
      }
    
      cin.get();
      return 0;
    }
    
    void nfound( const std::string &v_file ) {
      using namespace std;
      ofstream a_file ( "v_file" );
      a_file << "This text will go inside!NEWLINE";
      a_file.close();
    }
    Errors:
    |9|error: expected ',' or ';' before 'const'|
    ||In function 'int main(int, char**)':|
    |21|error: 'nfound' was not declared in this scope|

  2. #2
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    You need semi-colons after the definitions of NEWLINE and NEWLINE_FLUSH.

    I suspect, once you fix that, your code will not behave as you expect, as std::string's do not participate in concatenation of string literals. But you can experience that problem for yourself.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy in reply to you, it is likely you deserve it. Suck it up, sunshine, and read this, this, and this before posting again.

  3. #3
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    Colon Cancer

    The darn semi-colons! Thanks for pointing that out! Can you explain your comment here:
    Quote Originally Posted by grumpy View Post
    I suspect, once you fix that, your code will not behave as you expect, as std::string's do not participate in concatenation of string literals. But you can experience that problem for yourself.
    I've just began programming and the furthest explaination of strings was C-style vs std::string.

  4. #4
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    The code
    Code:
       a_file << "This text will go inside!NEWLINE";
    will put the text "NEWLINE" into your output file, whereas I suspect you expect there to be an actual newline.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy in reply to you, it is likely you deserve it. Suck it up, sunshine, and read this, this, and this before posting again.

  5. #5
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    Wouldn't this code here replace anywhere that I put NEWLINE with \n? Kinda like an alias, that is the intended affect anyway...
    Code:
    const std::string NEWLINE = "\n"

  6. #6
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    That is my point. Look at the output file. You will find it does not.

    Aliasing of variable names does not work inside string literals.

    Think about it: would you really want the output of "some_stream << "Hello Peter"; to change if you subsequently modified the code to introduce a variable or macro in your code named Peter?
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy in reply to you, it is likely you deserve it. Suck it up, sunshine, and read this, this, and this before posting again.

  7. #7
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    Oh I see now! So something to the tune of:
    Code:
    a_file << "This text will go inside!" << NEWLINE;

  8. #8
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    What benefit that gives you over
    Code:
    a_file << "This text will go inside!" << "\n";
    is questionable.

    Note that it will not work with your definition of NEWLINE_FLUSH, as std::endl is not a character string.
    Right 98% of the time, and don't care about the other 3%.

    If I seem grumpy in reply to you, it is likely you deserve it. Suck it up, sunshine, and read this, this, and this before posting again.

  9. #9
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    The benefit is psychological, it might change later on when I advance through the tutorials and start actually programming. As for NEWLINE_FLUSH, I don't know how to make that one an alias, but I did it to highlight to myself that there is an alternative version to doing a newline.

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