Thread: strlwr() and delimiter removal

Well as of your first function, strlwr() is looking for a const char *, you are supplying a std::string so the quick fix for this is to edit the call to strlwr() like so:

Code:

strlwr(s.c_str());

Not sure about the rest...

Originally Posted by kryptkat

after doing several searchs i found transform() i would like to stick with strlwr() that i know for now. read through thinking in cpp vol 1. looking for some type of clue to get it working. even tried strlwr(&s) nope.

The problem is that strlwr(), which is not in the C++ standard library, changes the string. As such, jeffcobb's suggestion does not work.

So, you have a few choices: you could allocate space for a null terminated string, copy over the contents of your std::string, and only then apply strlwr(), but then you will be stuck with a null terminated string whose allocated memory needs to be managed manually.

Alternatively, you could pass &s[0] as the argument, but it is not guaranteed to work at this point of time, though it most likely will (but you should push_back() a null character before using it in this way). You can avoid this uncertainty by using a std::vector<char> and passing &v[0] instead, where v is the vector with enough space to store the null terminated string... but frankly you are better off learning how to use transform().

Originally Posted by laserlight

The problem is that strlwr(), which is not in the C++ standard library, changes the string. As such, jeffcobb's suggestion does not work.
.

My mistake, just looked it up, thought it did take a const char * but nope I was wrong. Just checked some old code, I did it once like so:

Code:

string myStrLwr(string in)
{
   string strOut = "";
   for(unsigned pos = 0; pos < in.size(); pos++)
   {
      char c = tolower(in.at(pos));
      strOut.push_back(c);
   }
   return strOut;

}

Sorry for the confusion...

Jeff

Note: this *does* work; just recompiled and tested myself ^__^

Ah, but then you might as well use std::transform, e.g.,

Code:

string myStrLwr(string in)
{
    transform(in.begin(), in.end(), in.begin(), ::tolower);
    return in;
}

Originally Posted by laserlight

Ah, but then you might as well use std::transform, e.g.,

Code:

string myStrLwr(string in)
{
    transform(in.begin(), in.end(), in.begin(), ::tolower);
    return in;
}

Yep might as well. YAWTSAC (Yet Another Way To Skin A Cat)...I never said this was the only way, just what I had written some time ago that worked...

using transform() what about the delimiter removal ? how to use transform to remove delimiters ?

Code:

   while(words[i] != '.' | words[i] != ',' )   out << words[i] ;

when i tried to use "char q[] = "test string"; " in a class i got can not covert const string. so put it in main() also tried file read. i know the prob is std::string is not char *s or not pointer to char. is not string. transform requires vector ? or algorithm ? for include. do not understand why transform need begin twice ?

lazerlight
when return in is that in in memory or does it write back to file or second file like

Code:

string myStrLwr(string in)
{
    transform(in.begin(), in.end(), in.begin(), ::tolower);
    return in;
}
    out <<  in // filetwo.txt

thank you both

YAWTSAC (Yet Another Way To Skin A Cat)

<shudders>

Originally Posted by kryptkat

using transform() what about the delimiter removal ? how to use transform to remove delimiters ?

You need to elaborate on what exactly is this delimiter removal about.

Originally Posted by kryptkat

transform requires vector ? or algorithm ? for include.

<algorithm> is the correct header.

Originally Posted by kryptkat

do not understand why transform need begin twice ?

In my example, I am applying transform to the elements of the string, and then assigning the result to those same elements.

Originally Posted by kryptkat

when return in is that in in memory or does it write back to file or second file like

jeffcobb's myStrLwr example is a function that takes a std::string argument by value and returns a std::string object. It has nothing to do with files. Personally, I would have taken the argument by non-const reference and modified it as demonstrated in my example. In such a case, the return type can be void.

Originally Posted by kryptkat

i put that in main ().

It is a function definition, and functions cannot be defined within other functions.

Originally Posted by kryptkat

this is the error i got when i tried

Code:

string myStrLwr(string in)
{
    transform(in.begin(), in.end(), in.begin(), ::tolower);
    return in;
}

i was writing to files my bad. i put that in main ().

I've seen problems like that before, relating to the fact that tolower() is a macro. It's not SUPPOSED to be a macro if you include <cctype> instead of <ctype.h>, but some library implementations are broken, go figure. Try this:

Code:

char MyToLower( char ch )
{
    return tolower( ch );
}

string myStrLwr(string in)
{
    transform(in.begin(), in.end(), in.begin(), MyToLower);
    return in;
}

Originally Posted by laserlight

You need to elaborate on what exactly is this delimiter removal about.


<algorithm> is the correct header.


In my example, I am applying transform to the elements of the string, and then assigning the result to those same elements.


jeffcobb's myStrLwr example is a function that takes a std::string argument by value and returns a std::string object. It has nothing to do with files. Personally, I would have taken the argument by non-const reference and modified it as demonstrated in my example. In such a case, the return type can be void.

I should have done it by reference but figured the heart of the method was what was of educational value (if any)...as for doing it as a file, I would have mmapped the file and iterated over the contents that way...simple and fast.

// 'out' now contains a lowercased version of in

ok it compiles but how do you get it to write to the file ? i tried out << out and nothing in the file. have been using string s and doing out << s which works. so would something like

Code:

  string s; 
   out << s(out) ;

work ?

nope got

44 C:\Dev-Cpp\project333 misc\stringtolowercvc.cpp no match for call to `(std::string) (std::ofstream&)'