Help in strings

This is a discussion on Help in strings within the C++ Programming forums, part of the General Programming Boards category; Hello all. Getting to the point, I need some help in string functions. I was making a program to implement ...

  1. #1
    Cryptanalyst
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    Sep 2007
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    Help in strings

    Hello all. Getting to the point, I need some help in string functions. I was making a program to implement my own string functions, without using string.h
    The program turns out proper and correct, but one little flaw remains and that appears in the execution. For this snippet of code -:
    Code:
     cout << "\nEnter 2 strings - ";
    gets(str1);
    fflush(stdin);
    gets(str2);
    fflush(stdin);
    The computer accepts only one string and not the other. Why is this so? Even if I try
    Code:
    cout << "\nEnter 1 string - ";
    gets(str1);
    fflush(stdin);
    cout << "\nEnter 2nd string - ";
    gets(str2);
    fflush(stdin);
    It doesn't work. Will be grateful if you help ASAP.
    Last edited by SVXX; 12-09-2008 at 12:03 AM.

  2. #2
    C++ Witch laserlight's Avatar
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    Maybe your implementation of gets() is wrong. Oh wait, why bother implementing the terribly unsafe gets() in the first place? Have you considered designing and implementing a cleaner version of std::string instead?

    By the way, fflush(stdin) results in undefined behaviour. There are other ways to "flush" the input buffer that do not result in undefined behaviour; see the cprogramming.com FAQs.
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  3. #3
    Cryptanalyst
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    Hmm..I checked that. Then I suppose this is how I would go about it -:
    Code:
    cout << "\nEnter 2 strings - ";
    int ch;
    char buf[BUFSIZ];
    while((ch = cin.get()) != '\n && ch != EOF);
            {
                gets(str1);
                cout.flush();
                gets(str2);
                cout.flush();
            }
    Edit : Ah yes its working now. Thanks a bunch!
    Last edited by SVXX; 12-09-2008 at 12:27 AM.

  4. #4
    Registered User C_ntua's Avatar
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    It does? You read the first character, check it and then read the rest of the line with gets(). Won't you miss a character like that? And why do you fflush cout?

  5. #5
    Kernel hacker
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    Let me guess - there is a scanf/cin >> to read a number before this function - so your clearing of the input buffer allows the left-over newline that was in the input buffer to be cleared. This would be the 112th time someone has posted about this since I joined the forum.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
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  6. #6
    C++まいる!Cをこわせ! Elysia's Avatar
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    And you are still using gets.
    Get rid of it.
    http://cpwiki.sourceforge.net/Gets
    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.

  7. #7
    Cryptanalyst
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    Alright..I've been berated too much for gets(). Let it never haunt thy mind again! xD.
    For the alternative, I used something a little simpler. Please do tell me if this method is safe from buffer overflows. And no, I wasn't entering a number before the string or anything, mat. I was making a program implementing my own functions for string operations, without using anything in string.h.

    Code:
    cout << "\nEnter a string - ";
    cin.ignore(); //Ignores the newline
    cin.getline(str1, 200);

  8. #8
    C++まいる!Cをこわせ! Elysia's Avatar
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    std::string str;
    std::getline(std::cin, str);
    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.

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