Compare Two Strings?

This is a discussion on Compare Two Strings? within the C++ Programming forums, part of the General Programming Boards category; Code: ifstream input_file("input.txt"); string line; getline( input_file, line, '\n' ); line now has the first line of the file: "C++Draw ...

  1. #1
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    Compare Two Strings?

    Code:
    	ifstream input_file("input.txt");
    	string line;
    	getline( input_file, line, '\n' );
    line now has the first line of the file: "C++Draw Object File V1.0"

    Now I do:

    Code:
    	cout << line.compare("C++Draw Object File V1.0") << "\n";
    	cout << line.compare("C++Draw Object Fidle V1.0") << "\n";
    Notice the misspelling on the word File in line 2.

    The first line prints: "1"
    The second line prints: "1"

    Wtf?? How can they be the same??

    How do I compare strings correctly?
    Last edited by Paul22000; 05-24-2008 at 03:27 PM.

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Compare returns 0 if the strings match correctly. If you read the documentation for std::string.compare, you would understand more.
    The more proper way of comparing strings is simply
    Code:
    	cout << (line == "C++Draw Object File V1.0") << "\n";
    	cout << (line == "C++Draw Object Fidle V1.0") << "\n";
    Last edited by Elysia; 05-24-2008 at 03:49 PM.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  3. #3
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    Are you sure? I'm getting:

    main.cpp:39: error: invalid operands of types ‘const char [25]’ and ‘const char [2]’ to binary ‘operator<<’
    main.cpp:40: error: invalid operands of types ‘const char [26]’ and ‘const char [2]’ to binary ‘operator<<’

    -------------------------
    Edit:

    I put parenthesis around them like so:

    cout << (line == "C++Draw Object File V1.0") << "\n";
    cout << (line == "C++Draw Object Fidle V1.0") << "\n";

    Compiles, but now BOTH lines output 0.

  4. #4
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    0 means false.

    What both your original code and the latest version are saying is that your strings are different than what is in the file.

  5. #5
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    Quote Originally Posted by Daved View Post
    0 means false.

    What both your original code and the latest version are saying is that your strings are different than what is in the file.
    Right...

    I'm asking how to make it work properly hehe.

    Even when the text of the strings are exactly the same ("C++Draw Object File V1.0"), it STILL gives false.

    THIS is what I am asking on how to fix.

  6. #6
    Cat without Hat CornedBee's Avatar
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    Have you examined the string to find out if it is really what you expect?
    Code:
    std::cout << "'" << line << "'\n";
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  7. #7
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    Quote Originally Posted by CornedBee View Post
    Have you examined the string to find out if it is really what you expect?
    Code:
    std::cout << "'" << line << "'\n";
    Genius!

    'C++Draw Object File V1.0 '

    (Has a blank at the end)

    After some Googling, I found that I should probably use string.find() instead. This will avoid this pesky problem in case the professor's input file has spaces at the end. Thanks all.

    If anyone has a better solution than string.find(), definitely post it. This thread is on my email subscription list (instant email hehe)
    Last edited by Paul22000; 05-24-2008 at 04:42 PM.

  8. #8
    Cat without Hat CornedBee's Avatar
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    Genius!
    Experienced.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  9. #9
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    Haha! Yes I will save this in my brain alongside the dreaded "if ( a = b )" mistake

  10. #10
    and the hat of sweating
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    Quote Originally Posted by Paul22000 View Post
    Haha! Yes I will save this in my brain alongside the dreaded "if ( a = b )" mistake
    Well that's one bug the compiler should find for you (assuming you turn your Warning Levels high enough).

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