transform help!!!

this maybe to easy for some of you but i want to do transform this string:

this_is_a_string

to this...

this is a string

i want the underscores to be replaced by spaces and vice versa... i want also to use transform stl (although lately stls hates me )
for this to work but i seem not to do it quite right... i know that transform needs unary operators so i created one but it give me trouble because it needs a argument... here is my code

my unary_operators

Code:

    //unary functions.. for transforming  space to _
    struct trans_under : std::unary_function<char , char>
    {
        char operator () (char & in) const
        {
            if (in == '_'){
                return ' ';
            }else{
                return in;
            }
        }
    }tunder;

    //unary functions.. for transforming _ to space
    struct trans_space : std::unary_function<char , char>
    {
        char operator () (char & in) const
        {
            if (in == ' '){
                return '_';
            }else{
                return in;
            }
        }
    }tspace;

and here is my transform...

Code:

                std::string str;
                file >> str;
                
                //doesn't work because tunder needs parameters??
                std::transform(str.begin(), str.end(), str.begin(), tunder());

i look on bunch of stuffs in google and i find nothing with having your own unary operators.. it's always about lower case and upper case.

please help and more power!

i have answered my own question! i think.... i should have done this...

Code:

std::transform(str.begin(), str.end(), str.begin(), tunder);

or this...

Code:

std::transform(str.begin(), str.end(), str.begin(), trans_under());

i should pay more attention to the tutorials...

now could anyone will be kind enough to explain to me why is this so? i thought that when i did tunder() i am invoking my overloaded operator()...

and with regards with the solution, which one would be the better?

thanks again! (you know, i might never find out the answer this quickly if i never tried to make this thread )

You don't really need to use transform()

There are much simpler ways...

http://www.cprogramming.com/tutorial/string.html

Try using my_string.replace()

If you're really crazy you could totally ignore the fact that there is a standard library solution and hack it together with char buffers. I've done it a few times.

Now let's never speak of this again.

There's also replace_if:

Code:

#include <iostream>
#include <string>
#include <functional>
#include <algorithm>
using namespace std;

int main()
{
    string str = "This_is_a_string";

    cout << str << endl;

    replace_if(str.begin(),str.end(),bind1st(equal_to<char>(),'_'),' ');

    cout << str << endl;

    return 0;
}

Output:

Code:

This_is_a_string
This is a string

[edit]
You can even use for_each:

Code:

#include <iostream>
#include <string>
#include <functional>
#include <algorithm>
using namespace std;

template<char char_to_find,char char_to_replace>
class replaceit
{
public:
    operator()(char& c)
    {
        if( c == char_to_find ) c = char_to_replace;
    }
};


int main()
{
    string str = "This_is_a_string";

    cout << str << endl;

    for_each(str.begin(),str.end(),replaceit<'_',' '>());

    cout << str << endl;

    return 0;
}

Should output the same thing.
[/edit]

i tried looking at string.replace() it seems that i may have a rather harder time to implement it.

i don't like to use char buffers so i do it using STL.

i never knew replace_if until now. i think it's good from what i have read.

thanks!

Originally Posted by hk_mp5kpdw

There's also replace_if:


[edit]
You can even use for_each:

Code:

#include <iostream>
#include <string>
#include <functional>
#include <algorithm>
using namespace std;

template<char char_to_find,char char_to_replace>
class replaceit
{
public:
    operator()(char& c)
    {
        if( c == char_to_find ) c = char_to_replace;
    }
};


int main()
{
    string str = "This_is_a_string";

    cout << str << endl;

    for_each(str.begin(),str.end(),replaceit<'_',' '>());

    cout << str << endl;

    return 0;
}

Should output the same thing.
[/edit]

just to be pedantic, that's technically incorrect. the standard dictates that for_each should be a non mutating operation, but I don't know any implementation that actually enforces this, probably because it's a stupid idea.

i learn i could also do this

Code:

std::replace(str.begin(), str.end(), '_', ' ');