So my problem is next:
I have youtube link entered as input, and I should print youtubeID as output.
So, perhaps I have this link: https://www.youtube.com/watch?v=szyKv63JB3s , I should print this "szyKv63JB3s", so I came to conclusion that I need to find that " = " in user inputed string and I should look to make new string called "ytID" or "result" and store youtubeID from the moment I find that " = " characther.
So I really don't have idea how should it be done...
I mean I should go through string with for loop I guess, and after that I should store the part which will be called youtubeID, and I have problem there because I don't know how long is that link, I mean how much characthers it have, so I cannot really use for or while loops...
P.S This is not HOMEWORK, I just want to practice. :)
you should give a look at this post :
Removing everything after character (and also character)
A solution could be as simple as :
theString.substr( theString.find('=') ) ;
Just search for the character = as you mentioned in the question:
#include <iostream>
#include <string_view>
std::string_view extractYoutubeId(std::string_view const link) {
auto const off = link.find('=');
if (off == std::string_view::npos)
return std::string_view{};
return link.substr(off + 1);
}
int main() {
auto const& link = "https://www.youtube.com/watch?v=dQw4w9WgXcQ";
std::cout << extractYoutubeId(link);
}
Output: dQw4w9WgXcQ
Related
I'm trying to recognise certain phrases within a user defined string but so far have only been able to get a single word.
For example, if I have the sentence:
"What do you think of stack overflow?"
is there a way to search for "What do you" within the string?
I know you can retrieve a single word with the find function but when attempting to get all three it gets stuck and can only search for the first.
Is there a way to search for the whole string in another string?
Use str.find()
size_t find (const string& str, size_t pos = 0)
Its return value is the starting position of the substring. You can test if the string you are looking for is contained in the main string by performing the simple boolean test of returning str::npos:
string str = "What do you think of stack overflow?";
if (str.find("What do you") != str::npos) // is contained
The second argument can be used to limit your search from certain string position.
The OP question mentions it gets stuck in the attempt to find a three word string. Actually, I believe you are misinterpreting the return value. It happens that the return for the single word search "What" and the string "What do you" have coincidental starting positions, therefore str.find() returns the same. To search for individual words positions, use multiple function calls.
Use regular expressions
#include <iostream>
#include <string>
#include <regex>
int main ()
{
std::string s ("What do you think of stack overflow?");
std::smatch m;
std::regex e ("\\bWhat do you think\\b");
std::cout << "The following matches and submatches were found:" << std::endl;
while (std::regex_search (s,m,e)) {
for (auto x:m) std::cout << x << " ";
std::cout << std::endl;
s = m.suffix().str();
}
return 0;
}
Also you can find wildcards implementing with boost (regex in std library was boost::regex library before c++11) there
Consider the following string content:
string content = "{'name':'Fantastic gloves','description':'Theese gloves will fit any time period.','current':{'trend':'high','price':'47.1000'}";
I have never used regex_search and I have been searching around for ways to use it - I still do not quite get it. From that random string (it's from an API) how could I grab two things:
1) the price - in this example it is 47.1000
2) the name - in this example Fantastic gloves
From what I have read, regex_search would be the best approach here. I plan on using the price as an integer value, I will use regex_replace in order to remove the "." from the string before converting it. I have only used regex_replace and I found it easy to work with, I don't know why I am struggling so much with regex_search.
Keynotes:
Content is contained inside ' '
Content id and value is separated by :
Conent/value are separated by ,
Value of id's name and price will vary.
My first though was to locate for instance price and then move 3 characters ahead (':') and gather everything until the next ' - however I am not sure if I am completely off-track here or not.
Any help is appreciated.
boost::regex would not be needed. Regular expressions are used for more general pattern matching, whereas your example is very specific. One way to handle your problem is to break the string up into individual tokens. Here is an example using boost::tokenizer:
#include <iostream>
#include <string>
#include <boost/tokenizer.hpp>
#include <map>
int main()
{
std::map<std::string, std::string> m;
std::string content = "{'name':'Fantastic gloves','description':'Theese gloves will fit any time period.','current':{'trend':'high','price':'47.1000'}";
boost::char_separator<char> sep("{},':");
boost::tokenizer<boost::char_separator<char>> tokenizer(content, sep);
std::string id;
for (auto tok = tokenizer.begin(); tok != tokenizer.end(); ++tok)
{
// Since "current" is a special case I added code to handle that
if (*tok != "current")
{
id = *tok++;
m[id] = *tok;
}
else
{
id = *++tok;
m[id] = *++tok; // trend
id = *++tok;
m[id] = *++tok; // price
}
}
std::cout << "Name: " << m["name"] << std::endl;
std::cout << "Price: " << m["price"] << std::endl;
}
Link to live code.
As the string you are attempting to parse appears to be JSON (JavaScript Object Notation), consider using a specialized JSON parser.
You can find a comprehensive list of JSON parsers in many languages including C++ at http://json.org/. Also, I found a discussion on the merits of several JSON parsers for C++ in response to this SO question.
Apologies in advance, because I suspect this may be a silly question.
I have written a function for reading in data from an external file. I then use the data to perform calculations using other code I have written.
The function works by finding a data label that looks like this:
const std::string findMe = "<dataLabel>";
Each time I want to find data, I replace dataLabel with the label of whichever data I need from the file.
Here's what I want to do.
I don't want to have to write in the label of the data I want each time. I want to be able to do this:
for (int i = 0; i < anyNumberOfDataSets; i++)
{
findMe = "<dataLabeli>";
// Then run function for reading in data, put data into a vector.
}
I could then add any number of data sets to my external file, give each one the title
, and have each data set read into a vector.
The problem is, I simply can't figure out how to write findMe = "<dataLabeli>". Is this even possible?
I have tried things like, findMe = "<dataLabel" << i <<, but no luck!
Any suggestions would be much appreciated.
It is very hard to understand what you mean, but I guess you want this
#include <sstream>
#include <string>
for (int i = 0; i < anyNumberOfDataSets; i++)
{
std::ostringstream strm;
strm << "<dataLabel" << i << ">";
const std::string findMe = strm.str();
//...
//proceed with searching findMe
}
You can read more about string streams, for instance, here
you've already got the right answer, so this is just trying to help you with solving such problems in the future:
Your core problem here is to convert the integer i into a string s (if you've done this, than you just do findMe = "<datalabel"; findMe += s; findMe += ">";.
Googling for c++ convert integer into string will give you this as the first result. Problem solved.
This is not saying "use google before/instead of asking", it's rather "try to identify the core problem".
Another solution:
using namespace boost;
findMe = str(format("<dataLabel%d>") % i);
This will substitute %d with the value of i, formatted like printf() does.
ifstream toOpen;
openFile.open("sample.html", ios::in);
if(toOpen.is_open()){
while(!toOpen.eof()){
getline(toOpen,line);
if(line.find("href=") && !line.find(".pdf")){
start_pos = line.find("href");
tempString = line.substr(start_pos+1); // i dont want the quote
stop_pos = tempString .find("\"");
string testResult = tempString .substr(start_pos, stop_pos);
cout << testResult << endl;
}
}
toOpen.close();
}
What I am trying to do, is to extrat the "href" value. But I cant get it works.
EDIT:
Thanks to Tony hint, I use this:
if(line.find("href=") != std::string::npos ){
// Process
}
it works!!
I'd advise against trying to parse HTML like this. Unless you know a lot about the source and are quite certain about how it'll be formatted, chances are that anything you do will have problems. HTML is an ugly language with an (almost) self-contradictory specification that (for example) says particular things are not allowed -- but then goes on to tell you how you're required to interpret them anyway.
Worse, almost any character can (at least potentially) be encoded in any of at least three or four different ways, so unless you scan for (and carry out) the right conversions (in the right order) first, you can end up missing legitimate links and/or including "phantom" links.
You might want to look at the answers to this previous question for suggestions about an HTML parser to use.
As a start, you might want to take some shortcuts in the way you write the loop over lines in order to make it clearer. Here is the conventional "read line at a time" loop using C++ iostreams:
#include <fstream>
#include <iostream>
#include <string>
int main ( int, char ** )
{
std::ifstream file("sample.html");
if ( !file.is_open() ) {
std::cerr << "Failed to open file." << std::endl;
return (EXIT_FAILURE);
}
for ( std::string line; (std::getline(file,line)); )
{
// process line.
}
}
As for the inner part the processes the line, there are several problems.
It doesn't compile. I suppose this is what you meant with "I cant get it works". When asking a question, this is the kind of information you might want to provide in order to get good help.
There is confusion between variable names temp and tempString etc.
string::find() returns a large positive integer to indicate invalid positions (the size_type is unsigned), so you will always enter the loop unless a match is found starting at character position 0, in which case you probably do want to enter the loop.
Here is a simple test content for sample.html.
<html>
<a href="foo.pdf"/>
</html>
Sticking the following inside the loop:
if ((line.find("href=") != std::string::npos) &&
(line.find(".pdf" ) != std::string::npos))
{
const std::size_t start_pos = line.find("href");
std::string temp = line.substr(start_pos+6);
const std::size_t stop_pos = temp.find("\"");
std::string result = temp.substr(0, stop_pos);
std::cout << "'" << result << "'" << std::endl;
}
I actually get the output
'foo.pdf'
However, as Jerry pointed out, you might not want to use this in a production environment. If this is a simple homework or exercise on how to use the <string>, <iostream> and <fstream> libraries, then go ahead with such a procedure.
This looks like homework stuff but please be assured that it isn't homework. Just an exercise in the book we use in our c++ course, I'm trying to read ahead on pointers..
The exercise in the book tells me to split a sentence into tokens and then convert each of them into pig latin then display them..
pig latin here is basically like this: ball becomes allboy in piglatin.. boy becomes oybay.. take the first letter out, put it at the end then add "ay"..
so far this is what i have:
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
#include <cstring>
using std::strtok;
using std::strcat;
using std::strcpy;
void printPigLatin( char * );
int main()
{
char sentence[500];
char *token;
cout << "Enter string to tokenize and convert: ";
cin.getline( sentence, 500 );
token = strtok( sentence, " " );
cout << "\nPig latin for each token will be: " << endl;
while( token != NULL )
{
printPigLatin( token );
token = strtok( NULL, " " );
}
return 0;
}
void printPigLatin( char *word )
{
char temp[50];
for( int i = 0; *word != '\0'; i++ )
{
temp[i] = word[i + 1];
}
strcat( temp, "ay" );
cout << temp << endl;
}
I understand the tokenizing part quite clearly but I'm not sure how to do the pig latin.. i tried to start by simply adding "ay" to the token and see what the results will be .. not sure why the program goes into an infinite loop and keeps on displaying "ayay" .. any tips?
EDIT: this one works fine now but im not sure how to add the first letter of the token before adding the "ay"
EDIT: this is how i "see" it done but not sure how to correctly implement it ..
You're running over your input string with strcat. You need to either create a new string for each token, copying the token and "ay", or simply print the token and then "ay". However, if you're using C++ why not use istream iterators and STL algorithms?
To be honest, I severly doubt the quality of the C++ book, judging from your example. The “basic stuff” in C++ isn't the C pointer style programming. Rather, it's applying high-level library functionality. As “On Freund” pointed out, the C++ standard library provides excellent features to tackle your task. You might want to search for recommendations of better C++ books.
Concerning the problem: your printPigLatin could use the existing function strcpy (or better: strncpy which is safer in regards to buffer overflows). Your manual copy omits the first character from the input because you're using the i + 1st position. You also have a broken loop condition which always tests the same (first) character. Additionally, this should result in an overflow anyway.
As the people before me pointed out, there are several other methods of achieving what you want to do.
However, the actual problem with your code seems to be the use of strcat, I see that you changed it a bit in the edit. Here is an explanation of why the initial one did not work char* and size issues
Basically, the pointer does not allocate enough memory to add the "ay" to the string provided. If you create a pointer using the technique shown in the link, it should work fine.
I got your program to work, taking the strcat out and using
cout << word << "ay" << endl
Your loop is infinite because of *word != '\0'.
The word pointer is not changed at any time in the loop.
This seemed to have worked:
void printPigLatin( char *word )
{
cout << word + 1 << word[0] << "ay" << endl;
}
Just not sure if it's a good idea to do that.