Really quick silly question.

How do I parse a "?

For example, I'm supposed to be coding a web crawler for this homework, and hyperlinks are enclosed in quotes. How do I do a

Code:

---

string word;
//code to fill in word

if (word[i] == "\"") {
//do stuff

---

I'm getting a warning about converting between integers and pointers :\

word[i] is one char - it should be compared to one char '\"' and not a string

Double quotes -> string.
Single quotes -> char.
Strings must be compared using strcmp.
Chars can be compared using regular comparison (==).

Quote:

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Strings must be compared using strcmp

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C-strings must be compared using strcmp
std::strings should be compared using ==

Fair enough.

Thanks, ' instead of " worked perfectly.

Another question ><. How to easily transform strings into lowercase? I hear theres a function StringToLower, but I cant seem to get my program to recognize it. I also try word[i].tolower(), but its also recognized. Halp plz? Thanks ^_^.

std::tolower.
Member functions are only available on classes.

Hrm, I'm missing something here. Its probably a preprocessor directive but the ones I'm finding on google arent doing me any good.

I have:

Code:

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string word = "Blah";
word = tolower(word);

---

Yet I receive a no matching function, candidates are INT tolower(INT).

So how do I do this for strings @_@?

Ah, it's only for characters... Hmm.
The Standard Library really does not shine when it comes to this... And MSDN's docs sucks on the matter.
Well, someone else should know.

Just loop through the word such as;

Code:

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          for (int a=0; a<word.length(); ++a)
            word[a]=tolower(word[a]);

---

Oh right, now that you told me how to use it, I can go back to my old loop. lol

Thanks guys!

Is this the quality of the standard library? Not even a function to make a lower case strings?

Quote:

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Originally Posted by Elysia

Is this the quality of the standard library? Not even a function to make a lower case strings?

---

Code:

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transform(source.begin(), source.end(), target.begin(),static_cast< int(*)(int) >(tolower));

---

The STL was made to be generic. A single function just to transform strings to lower would be too specific. This unfortunately looks a little bad with the cast, but it's necessary because there are two tolower functions.

Ah ha, another questions ><. I'm trying to declare another in file stream, and its in a function outside of the main.

Code:

---

bool Crawl(blah) {
    ...
    for (int i = 0; i < hyperlinks.size(); i++) {
        std::ifstream next_page(hyperlinks[i]);
        if (next_page) {Crawl(web, next_page, hyperlinks[i]);}
        next_page.close();
    }
    ...
}

---

It doesnt like this :\. No matching function calls again

Is hyperlinks a vector of std::string?

Quote:

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Originally Posted by King Mir

Code:

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transform(source.begin(), source.end(), target.begin(),static_cast< int(*)(int) >(tolower));

---

The STL was made to be generic. A single function just to transform strings to lower would be too specific. This unfortunately looks a little bad with the cast, but it's necessary because there are two tolower functions.

---

Horrible solution to a fundamental problem IMO.

Yes it is.

I cant even begin to understand the line of code mir posted, heh.

Then try
std::ifstream next_page( hyperlinks[i].c_str() );

Quote:

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Originally Posted by Elysia

Horrible solution to a fundamental problem IMO.

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If your talking about the cast, I agree.

But the transform is exactly the right tool for this. You want to convert each element in a STL container. Transform is the function designed to do this.

Yes it is.

I can't even begin to comprehend the line of code mir posted, haha.

EDIT: I know about second pages, totally :\.

Thanks elysia, worked like a charm =).

The cast makes it even more horrible.
You shouldn't have to call a "transform" function just to convert each character in a string. It's a string class, so provide a tolower function, even if it's just in the std namespace. It could just be a wrapper for transform, but it should exist.
The more I find out about the standard library, the more poorly designed it seems to me. I'm just at odds with it.

What do you prefer to use? is there like an 'alternate STL'? Or do you just code it all from scratch yourself @_@?

MFC is what I tend to use.

Sigh heh. Ok, now I'm getting segfaults. My intuition (which is often wrong as a novice programmer) tells me that it has to do with the fact that I'm calling this Crawl function from within itself...yet using an infile stream. I.e.

Crawl instance 1 calls crawl instance 2 with an ifs called next_page.
Crawl instance 2 then tries to call crawl instance 3 with an ifs ALSO called next_page. I just tried adding in a ifs.close() in the Crawl function before it calls any more, but that didn't fix it.

Any hints? :x I'll gladly provide any more information you need.

EDIT: On the topic of STL v MFC. So the...microsoft foundation library (?) has a better set of tools? Is it more widely used?

Quote:

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Originally Posted by Jozrael

Crawl instance 1 calls crawl instance 2 with an ifs called next_page.
Crawl instance 2 then tries to call crawl instance 3 with an ifs ALSO called next_page. I just tried adding in a ifs.close() in the Crawl function before it calls any more, but that didn't fix it.

Any hints? :x I'll gladly provide any more information you need.

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Segfault can mean a lot. If you don't have a debugger, try adding things such as cout to see if it's indeed a stack overflow.
Otherwise it can be memory corruption.
Posting code here can also help others help you debug your code.

Quote:

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EDIT: Oh, also whats MFC stand for?

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Microsoft Foundation Classes

Quote:

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Originally Posted by Jozrael

Yes it is.

I can't even begin to comprehend the line of code mir posted, haha.

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I wrote a nice long post to explain it all, but it got deleted when I accidentally pressed alt-left on my browser.

I will say this:
It does exactly what it says. Transform -- read convert -- each element in the range from the start to the end of the string, put the result in the target string -- which can be the same string . The conversion function is given as tolower. It helps to know that transform does elem=func(elem) for each element.

I'm fairly sure its memory corruption. I have a map of strings and a class called 'page' (i'm simulating a web crawler) and I just found out that none of the info is actually being stored in the map properly. When I try to access it, segfault.

>> So the...microsoft foundation library (?) has a better set of tools?
No.

They are different. One is standard and works everywhere you have a modern C++ compiler. MFC is for windows and Visual Studio only. If you have an MFC application for other reasons, then you might want to use some of the MFC containers, but otherwise stick to the standard classes.

Also, Elysia's opinion on the standard library interface is different than many C++ experts. Just because one person doesn't like the setup doesn't mean it's bad. (Of course, just because the C++ standards committee decided on the standard interface doesn't mean it's perfect either.)

EDIT: I'm a retard. Fixed. lol.

Edit: Foot in mouth x2?

Quote:

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Originally Posted by King Mir

Code:

---

transform(source.begin(), source.end(), target.begin(),static_cast< int(*)(int) >(tolower));

---

The STL was made to be generic. A single function just to transform strings to lower would be too specific. This unfortunately looks a little bad with the cast, but it's necessary because there are two tolower functions.

---

I skipped the cast and it worked just fine. I wasn't aware of transform, t'is a little neater than the old brute force method.

Code:

---

  void lowerCase(std::string &s)
      {

      std::transform(s.begin(), s.end(),
      s.begin(), std::tolower);

      std::cout<<s;  //Optional
      }

  lowerCase(anyString);

---

Quote:

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Originally Posted by Jozrael

EDIT: On the topic of STL v MFC. So the...microsoft foundation library (?) has a better set of tools? Is it more widely used?

---

As Daved says, it's a Microsoft-only library. It's a big framework with lots of classes, including GUI. I tend to use it for GUI and the rest of the classes simply because it's more tuned to how I like things. Everyone is different so there isn't any better or worse. They are different libraries with different purpose.

Code:

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#include <string>
#include <algorithm>
#include <iostream>
#include <ostream>
#include <cctype>

int main ( )
{
    const std::string test( "CAPS LOCK IS CRUISE CONTROL FOR COOL" );
    std::string lower( test );
    std::transform( test.begin(), test.end(), lower.begin(), ::tolower );
    std::cout << test << std::endl;
    std::cout << lower << std::endl;
}

---

If you find case conversions hard (and need to do lots of string processing), downloading boost is an option. Most of it, including string algorithms, is headers only, so there are no installation difficulties.
boost contains a number of nice string algorithms, for example for case conversion.

Boost seems a big, very nice library overall, as well, but it seems large and it could be difficult to know exactly what's in it.
It would be nice if the wiki pages could be updated with information about it.

Aside from string::tolower, string::toupper. I think there is also no such function as string::equals_ignore_case?

EDIT: I could not find an equalsIgnoreCase function in QString (Qt) class also! :(

But then operator == becomes case insensitive when you temporarily make both operands the same case beforehand anyway, like my example or a number of others demonstrates.

Again, case insensitive string comparisons are available in boost :)

As to it being large - naturally you won't need everything boost offers, and it does have quite well structured references (offline references come with the download if I'm not mistaken).