Replacing characters

This is a discussion on Replacing characters within the C++ Programming forums, part of the General Programming Boards category; Hey, I would like to replace every character in a string that is not a-z A-Z 0-9 or ' with ...

  1. #1
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    Replacing characters

    Hey,

    I would like to replace every character in a string that is not a-z A-Z 0-9 or ' with a space. Currently I am trying to approach it this way:

    Code:
    replace(ss.begin(), ss.end(), '!', ' ');
    Which would require dozens of those statements, one for each character that I don't want. Is there anyway to have the program check the string and convert any character that is not a-zA-Z' with a space, instead of writing individual replace statements?
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  2. #2
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    Use transform. Write a function that takes a character and returns that character if it is alphanumeric, or ' ' if it is not.
    It is too clear and so it is hard to see.
    A dunce once searched for fire with a lighted lantern.
    Had he known what fire was,
    He could have cooked his rice much sooner.

  3. #3
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    So something like this?

    Code:
    #include <ctype.h>
    
    char checkVal(char x)
    {
      if(isalnum(x))
        return x;
      else
        return " ";
    }
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  4. #4
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    >> return " "
    That should be return ' ' (use single quotes for characters).

    You need to call that in a loop on each character in your string. Using the transform function from <algorithm> can help you do that in one line of code.

  5. #5
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    So if I wanted to convert every character that is not a letter, ', or a space to a space, the code would be:

    Code:
    string modifyWord(string ss)
    {
    
        for(int xx = 0; xx < (int)ss.length(); xx++)
        {
            ss[xx] = tolower(ss[xx]);
            if(!isalpha(ss[xx]) && ss[xx] != ' ' && ss[xx] != "'")
                ss[xx] = ' ';
        }
    
        return ss;
    }
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  6. #6
    Registered User hk_mp5kpdw's Avatar
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    Using the transform function as suggested:
    Code:
    #include <iostream>
    #include <string>
    #include <algorithm>
    #include <cctype>
    
    char checkVal(char x)
    {
        if(std::isalnum(x))
            return x;
        else
            return ' ';
    }
    
    int main()
    {
        std::string ss("ab$^&cdefg!@123");
    
        std::cout << ss << std::endl;
    
        std::transform(ss.begin(),ss.end(),ss.begin(),checkVal);
    
        std::cout << ss << std::endl;
    
        return 0;
    }
    Outputs:
    Code:
    ab$^&cdefg!@123
    ab   cdefg  123
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
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  7. #7
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    Why didn't you use checkVal in your loop? Instead you used different code that probably doesn't compile and doesn't do the same thing.

  8. #8
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    Ok, thanks. When I was trying it a different way however I came across a compiler error that intrigued me. The error was this:

    Code:
    18 main.cpp ISO C++ forbids comparison between pointer and integer
    And the code:

    Code:
    for(int xx = 0; xx < (int)ss.length(); xx++)
        {
            ss[xx] = tolower(ss[xx]);
            if(!isalpha(ss[xx]) && ss[xx] != "'")
                ss[xx] = ' ';
        }
    Just the statement if(!isalpha(ss[xx])) worked, but when I added && ss[xx] != " ' " (apostrophe), that error arose.
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  9. #9
    The larch
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    If you need to put the apostrophe character between character marks you need to escape it.

    I wouldn't take special measures to prevent a space being replaced with a space.

    Code:
            if(!isalpha(ss[xx]) && ss[xx] != ' ' && ss[xx] != '\'')
                ss[xx] = ' ';
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

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