tolower error

This is a discussion on tolower error within the C++ Programming forums, part of the General Programming Boards category; That's just a hand-coded transform()... Why do that when you already have it? And yeah, std::tolower is probably the right ...

  1. #16
    Frequently Quite Prolix dwks's Avatar
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    That's just a hand-coded transform()... Why do that when you already have it? And yeah, std::tolower is probably the right way.
    That's right. It was just another solution. I thought that perhaps the OP would like to see how transform() works.

    I caught you in mid-edit when you said you suspected back_inserter to be the problem... back_inserter DOES return an output iterator -- this is the whole purpose of it.
    Yes, I figured that out eventually . . . sorry, I edited it out because I thought no one would have had time to read it. Evidently someone did.
    dwk

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  2. #17
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Livijn View Post
    17 C:\Users\Fredrik\Desktop\main.cpp no matching function for call to `transform(__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::back_insert_iterator<std::string>, string_lower(const std::string&)::lower)'
    You can't put the lower class inside the function. Move it outside into the global space.

    EDIT: Also, you could try what dwks said, and use std::tolower instead of just tolower. I bet that would work. My system is apparently too "helpful." Good demonstration of why it's important to compile your code under different compilers
    Last edited by brewbuck; 05-30-2007 at 03:44 PM.

  3. #18
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by dwks View Post
    That's right. It was just another solution. I thought that perhaps the OP would like to see how transform() works.
    Looking inside the STL headers can be tremendously informative. All kinds of cool, inspiring stuff in there.

    Yes, I figured that out eventually . . . sorry, I edited it out because I thought no one would have had time to read it. Evidently someone did.
    I saw it only by accident

  4. #19
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    Quote Originally Posted by Livijn View Post
    17 C:\Users\Fredrik\Desktop\main.cpp no matching function for call to `transform(__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::back_insert_iterator<std::string>, string_lower(const std::string&)::lower)'
    Code:
    >   transform(str.begin(), str.end(), back_inserter(x), tolower);
    Code:
       transform(str.begin(), str.end(), back_inserter(x), ::tolower);
    I have no clue why. Apparently it finds the overloaded function this way. You can also create a custom to_lower(), and substitute that for tolower in the transform call.
    Code:
    char to_lower(char c)
    {
       return tolower(c);
    }

  5. #20
    Just Lurking Dave_Sinkula's Avatar
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    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  6. #21
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    Errors:
    C:/Dev-Cpp/include/ctype.h: In function `std::string string_lower(const std::string&)':
    C:/Dev-Cpp/include/ctype.h:63: error: too few arguments to function `int tolower(int)'
    main.cpp:17: error: at this point in file

    C:/Dev-Cpp/include/c++/3.4.2/bits/stl_algo.h: In function `_OutputIterator std::transform(_InputIterator, _InputIterator, _OutputIterator, _UnaryOperation) [with _InputIterator = __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _OutputIterator = std::back_insert_iterator<std::string>, _UnaryOperation = int]':
    main.cpp:17: instantiated from here
    C:/Dev-Cpp/include/c++/3.4.2/bits/stl_algo.h:789: error: `__unary_op' cannot be used as a function


    I'm getting annoyed :P

  7. #22
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    Can you post your latest code?

  8. #23
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    Code:
    #include <iostream>
    #include <cctype>
    #include <iterator>
    #include <algorithm>
    
    using namespace std;
    
    string string_lower(const string &str)
    {
           class lower
           {
                 public:
                        char operator()(char ch) { return tolower(ch); }
           };
    
       string x;
       transform(str.begin(), str.end(), back_inserter(x), std::tolower());
       return x;
    }
    
    int main(int argc, char *argv[])
    {
        //Alla våra svenska ord i en array
        string swedish[2];
        swedish[0] = "hej";
        swedish[1] = "vem";
        
        //Alla våra engelska ord i en array
        string english[2];
        english[0] = "hi";
        english[1] = "who";
        
        /*Alla ord ska ligga i ordning så att swedish[2] representerar det svenska ordet för english[2]*/
        //Precis XD
        
        string insert; //Namnet på stringen som användaren skriver in i
        int quantity = 3; //Hur många ord det finns + 1. Om det finns 2 frågor ska det vara 3 här. Om det är 4 frågor ska det vara 5 här.
        int done = 0; //Hur många ord som har blivit svarade
        int points = 0; //Hur många poäng man får
        
        //Skriver ut en text
        cout << "Här kommer du få svenska ord som du ska översätta!\nDå börjar vi!\n\n\n";
        
        //Kör en while-sats för att alla ord ska vara med
        while (done < quantity) 
        {
              cout << "Vad heter " << swedish[done] << " på engelska?\n"; //Skriver ut vad heter lala beronde på vilket ord det är
              cin >> insert; //Låter användaren skriva in ett ord
              
              string lower = string_lower(swedish[done]); //Gör alla bokstäver små
              
              if (english[done] == lower) //kollar om det är rätt
              {
                         points = points + 1; //Lägg till 1 poäng
              } 
        done++;
        }
        
        cout << "Du fick " << points << " poäng!";
    }

  9. #24
    Captain Crash brewbuck's Avatar
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    Don't put the parentheses on std::tolower.

    I realize the parentheses are confusing. The reason for the difference is that std::tolower is a FUNCTION, which can serve directly as the functor of the transform. On the other hand, the hand-cooked lower class is not a function, but a CLASS. When you INSTANTIATE the class (using the () after the name, which is a constructor call), you get an OBJECT which acts as a functor.

    When you add the () to the end of std::tolower(), you actually CALL the function. This function returns an int, so the transform() call is getting passed an integer as a functor, which is invalid.

  10. #25
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    You should also #include <string> since you are using the string class.

  11. #26
    Frequently Quite Prolix dwks's Avatar
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    Quote Originally Posted by brewbuck View Post
    Don't put the parentheses on std::tolower.

    I realize the parentheses are confusing. The reason for the difference is that std::tolower is a FUNCTION, which can serve directly as the functor of the transform. On the other hand, the hand-cooked lower class is not a function, but a CLASS. When you INSTANTIATE the class (using the () after the name, which is a constructor call), you get an OBJECT which acts as a functor.

    When you add the () to the end of std::tolower(), you actually CALL the function. This function returns an int, so the transform() call is getting passed an integer as a functor, which is invalid.
    Some people prefer the syntax
    Code:
    &tolower
    because it makes it clear that you're taking the address of a function. It is, believe it or not, the same as
    Code:
    tolower
    just as
    Code:
    int (*to_something)(int) = tolower;
    to_something('a');
    is the same as
    Code:
    int (*to_something)(int) = tolower;
    (*to_something)('a');
    There are two arguments as to which is better. Personally, I use tolower and (*to_something)(). Don't ask me why.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
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  12. #27
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    Still gets an error:
    18 C:\Users\Fredrik\Desktop\main.cpp no matching function for call to `transform(__gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, __gnu_cxx::__normal_iterator<const char*, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::back_insert_iterator<std::string>, <unknown type>)'

    Code:
    Code:
    #include <iostream>
    #include <cctype>
    #include <iterator>
    #include <algorithm>
    #include <string>
    
    using namespace std;
    
    string string_lower(const string &str)
    {
           class lower
           {
                 public:
                        char operator()(char ch) { return tolower(ch); }
           };
    
       string x;
       transform(str.begin(), str.end(), back_inserter(x), tolower);
       return x;
    }
    
    int main(int argc, char *argv[])
    {
        //Alla v&#229;ra svenska ord i en array
        string swedish[2];
        swedish[0] = "hej";
        swedish[1] = "vem";
        
        //Alla v&#229;ra engelska ord i en array
        string english[2];
        english[0] = "hi";
        english[1] = "who";
        
        /*Alla ord ska ligga i ordning s&#229; att swedish[2] representerar det svenska ordet f&#246;r english[2]*/
        //Precis XD
        
        string insert; //Namnet p&#229; stringen som anv&#228;ndaren skriver in i
        int quantity = 3; //Hur m&#229;nga ord det finns + 1. Om det finns 2 fr&#229;gor ska det vara 3 h&#228;r. Om det &#228;r 4 fr&#229;gor ska det vara 5 h&#228;r.
        int done = 0; //Hur m&#229;nga ord som har blivit svarade
        int points = 0; //Hur m&#229;nga po&#228;ng man f&#229;r
        
        //Skriver ut en text
        cout << "H&#228;r kommer du f&#229; svenska ord som du ska &#246;vers&#228;tta!\nD&#229; b&#246;rjar vi!\n\n\n";
        
        //K&#246;r en while-sats f&#246;r att alla ord ska vara med
        while (done < quantity) 
        {
              cout << "Vad heter " << swedish[done] << " p&#229; engelska?\n"; //Skriver ut vad heter lala beronde p&#229; vilket ord det &#228;r
              cin >> insert; //L&#229;ter anv&#228;ndaren skriva in ett ord
              
              string lower = string_lower(swedish[done]); //G&#246;r alla bokst&#228;ver sm&#229;
              
              if (english[done] == lower) //kollar om det &#228;r r&#228;tt
              {
                         points = points + 1; //L&#228;gg till 1 po&#228;ng
              } 
        done++;
        }
        
        cout << "Du fick " << points << " po&#228;ng!";
    }

  13. #28
    Frequently Quite Prolix dwks's Avatar
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    Hmm, that's weird. On every compiler I have access to (Dinkumware's various ones) your source compiles perfectly.

    Did you re-compile it properly?
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


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  14. #29
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    I got Dev-C++ and it wont work

  15. #30
    Frequently Quite Prolix dwks's Avatar
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    Which version? Probably 4.9.something?

    It looks like your compiler is still having trouble figuring out what tolower is.
    Code:
    18 C:\Users\Fredrik\Desktop\main.cpp no matching function for call to `transform(
        ...::__normal_iterator<..., std::basic_string<...> >,
        ...::__normal_iterator<..., std::basic_string<...> >,
        std::back_insert_iterator<std::string>,
        <unknown type>)'
    So perhaps your tolower() is implemented as a macro or something. I'd suggest looking at <cctype> or going
    Code:
    #undef tolower
    to see if that is the case. If it is, you'll have to add a wrapper around tolower() as suggested.
    Code:
    int func_tolower(int c) { return tolower(c); }
    transform(str.begin(), str.end(), back_inserter(x), func_tolower);
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


    Other boards: DaniWeb, TPS
    Unofficial Wiki FAQ: cpwiki.sf.net

    My website: http://dwks.theprogrammingsite.com/
    Projects: codeform, xuni, atlantis, nort, etc.

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