Ordering C++ strings

This is a discussion on Ordering C++ strings within the C++ Programming forums, part of the General Programming Boards category; I tried using the strcmp function on a C++ string class and the compiler complains. I know C++ string is ...

  1. #1
    Registered User Vespasian's Avatar
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    Ordering C++ strings

    I tried using the strcmp function on a C++ string class and the compiler complains. I know C++ string is a class and C string character array but do they not still have the same features that strcmp can operate on?

    Secondly. I tried alphabetically ordering a vast number of words using the correct way through string::compare. Although they look ordered at first, after close inspection half of the words starting from the second letter onwards are unordered slightly like:

    ABC
    CIF
    CIB
    CI
    CHUTS
    CIRCLIP
    DOK

    I used the standard compare lines:
    str1.compare(str2 < 0) with no other parameters.
    So why does it do this?

    Thirdly and finally, what does the simple statement string1 < string2 do?

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by Vespasian View Post
    I tried using the strcmp function on a C++ string class and the compiler complains. I know C++ string is a class and C string character array but do they not still have the same features that strcmp can operate on?
    strcmp is oblivious to what a std::string is (it has no overload that takes a std::string), and no implicit conversion from std::string -> const char* exists, therefore it does not work. There is no need to use strcmp with std::string.

    Secondly. I tried alphabetically ordering a vast number of words using the correct way through string::compare. Although they look ordered at first, after close inspection half of the words starting from the second letter onwards are unordered slightly like:

    ABC
    CIF
    CIB
    CI
    CHUTS
    CIRCLIP
    DOK

    I used the standard compare lines:
    str1.compare(str2 < 0) with no other parameters.
    So why does it do this?
    I am going to take it you did...
    str1.compare(str2) < 0
    ...and if that is the case, you need to post an example of your code that demonstrates the problem.
    Otherwise, you have a bug (though I don't think it should compile).

    Thirdly and finally, what does the simple statement string1 < string2 do?
    The same thing as str1.compare(str2) < 0.
    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
    Registered User whiteflags's Avatar
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    string::compare is really for situations when you want to compare part of a string with another string.

  4. #4
    Registered User Vespasian's Avatar
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    Quote Originally Posted by Elysia View Post
    strcmp is oblivious to what a std::string is (it has no overload that takes a std::string), and no implicit conversion from std::string -> const char* exists, therefore it does not work. There is no need to use strcmp with std::string.


    I am going to take it you did...
    str1.compare(str2) < 0
    ...and if that is the case, you need to post an example of your code that demonstrates the problem.
    Otherwise, you have a bug (though I don't think it should compile).


    The same thing as str1.compare(str2) < 0.
    Here it is. Its a function that, depending on whether the word is less than or greater than, assigns the read node to the left leaf or right leaf of a binary tree node.

    Code:
    struct masternode* insert(struct masternode* node, string token) {
        if (node == NULL) {
            return(NewNode(token));
            }
        else {
            if (token.compare(node->token) < 0)
                node->left = insert(node->left, token);
            else if (token.compare(node->token) > 0)
                node->right = insert(node->right, token);
            else
                (node->count)++;
            return(node);
            }
    }

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