Searching a file for a String Occurence

This is a discussion on Searching a file for a String Occurence within the C++ Programming forums, part of the General Programming Boards category; Originally Posted by laserlight As in it does not actually do a case insensitive comparison? That would be because pStudent ...

  1. #31
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    Quote Originally Posted by laserlight View Post
    As in it does not actually do a case insensitive comparison? That would be because pStudent and pOStudent are pointers, so you are merely comparing addresses. You would need to use strcmp() if you really want to use C-style strings.
    My mind isn't working right today, I shouldn't have woken up to watch the BCS Championship earlier this morning. I need some coffee! Or a nap

    But it goes to show that I am reminded of something every day!

    Code:
    if(!strcmp(pStudent, pOStudent))
    ...
    Thanks!

    Now I will try the std::string route, once I have that figured out i'll post it.

    Cheers!
    Last edited by Phyxashun; 01-09-2009 at 10:52 AM.

  2. #32
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    Quote Originally Posted by Phyxashun
    But it goes to show that I am reminded of something every day!
    Personally, I would prefer to write:
    Code:
    if (strcmp(pStudent, pOStudent) == 0)
    The ! make me think of "not equal" instead of "equal"

    Quote Originally Posted by Phyxashun
    Now I will try the std::string route, once I have that figured out i'll post it.
    Incidentally, if you are trying to figure out my example, note that you need to #include <algorithm> for std::equal(). If you are trying to write a case insensitive "less than" comparator then the same idea applies, but you might use std::lexicographical_compare() instead of std::equal().
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #33
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    Thumbs up

    Quote Originally Posted by laserlight View Post
    The use of std::toupper (as opposed to the global toupper) is problematic in this case, though the exact reason eludes me at the moment. (Type mismatch? I know this has been discussed before.) Josuttis suggests just defining a function that compares characters without regard for case, and then use say, equal(), e.g.,
    Code:
    bool noCaseEqualChar(char lhs, char rhs)
    {
        return std::toupper(lhs) == std::toupper(rhs);
    }
    
    bool noCaseEqual(const std::string& lhs, const std::string& rhs)
    {
        return lhs.size() == rhs.size()
            && std::equal(lhs.begin(), lhs.end(), rhs.begin(), noCaseEqualChar);
    }
    We could use function object template classes instead and thus not have to resort to the different function names.
    These functions are absolutely perfect for use when comparing std::strings.

    Thanks laserlight!

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    Quote Originally Posted by laserlight View Post
    Josuttis suggests just defining a function that compares characters without regard for case, and then use say, equal(), e.g.,
    What page does Josuttis talk about that. I can't find it.

    Thanks in advance!

  5. #35
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    Quote Originally Posted by Phyxashun
    What page does Josuttis talk about that. I can't find it.
    In the 16th printing of The C++ Standard Library: A Tutorial and Reference, Josuttis talks about this case insensitive comparison on pages 499 to 501.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Once again, thanks.


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    Lightbulb Useful?

    This might be useful to someone:

    Code:
    /*******************************************************************************
    *   Usage:
    *       to_lower(std::string); Converts std::string to lowercase
    *       to_upper(std::string); Converts std::string to uppercase
    *******************************************************************************/
    #include <locale>
    #include <string>
    
    // to_lower(std::string)
    template <typename Char, typename Traits>
        std::basic_string<Char, Traits> &to_lower(std::basic_string<Char, Traits>
        &str, std::locale loc = std::locale())
    {
        typedef std::basic_string<Char, Traits> string;
        typedef std::ctype<Char> char_type;
        char_type const * the_type_ptr = &std::use_facet<char_type>(loc);
        for (typename string::size_type i = 0; i <str.size(); ++i)
        {
            str[i] = the_type_ptr->tolower(str[i]);
        }
        return (str);
    }
    
    // to_upper(std::string)
    template <typename Char, typename Traits>
        std::basic_string<Char, Traits> &to_upper(std::basic_string<Char, Traits>
        &str, std::locale loc = std::locale())
    {
        typedef std::basic_string<Char, Traits> string;
        typedef std::ctype<Char> char_type;
        char_type const * the_type_ptr = &std::use_facet<char_type>(loc);
        for (typename string::size_type i = 0; i <str.size(); ++i)
        {
            str[i] = the_type_ptr->toupper(str[i]);
        }
        return (str);
    }
    Cheers!

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    Talking

    This is what I settled on:
    Code:
    void searchRecords(std::ifstream &fin, std::string &searchString, 
                       OldStudentData &obj, long recordNum)
    {
        fin.seekg(sizeof(OldStudentData) * recordNum, std::ios::beg);
        fin.read((char *) &obj, sizeof(OldStudentData));
    
        std::string personName(obj.studentname);
    
        if(noCaseEqual(searchString, personName))
        {
            // Do some stuff in here!
        }
    }
    
    bool noCaseEqual(const std::string &lhs, const std::string &rhs)
    {
        return lhs.size() == rhs.size() 
            && std::equal(lhs.begin(), lhs.end(), rhs.begin(), noCaseEqualChar);
    }
    
    bool noCaseEqualChar(char lhs, char rhs)
    {
        return std::toupper(lhs) == std::toupper(rhs);
    }
    Thanks for all of the help! Any Ideas on refinement?

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