iamprakashom I am new to stringstream. I just copied this code from submission.
Can anyone please explain me, what is happening here? Thanks in advance :)
vector<int> parseInts(string str) { stringstream ss(str); //?? vector<int> result; char ch; int tmp; while(ss >> tmp) { //?? result.push_back(tmp); ss >> ch; //?? } return result;
pygospa Let me start with streams as such: streams are potentially endless sources of data input or data output. Take the STDIN, where potentially endless data can come in. Streams provide an interface to such an device, they capsulate it and provide means to get the information of such streams, or to put them into those devices.
In the first line with question mark (
stringstream ss(str)) you create a new stream. However this is a stringstream, so as source you do not provide a streaming device, but a string. As the text for the problem says, in C++ these streams are used for extraction of different data types in a string. So, what we get in line in question is a stringstream object called ss, that encapsulates a string, and allows as to access the string as we could access any other stream (remember that cin and cout are streams as well).Now to the second line.
ss >> tmpis a simple extraction. Remembercin >> afrom previous exercises. It does the same thing here: Get me the next thing on the stream (which actually is a string) and put it in the variabletmp. Now the trick is, thattmpis of typeint, so only if the next thing in the stream is an integer value will this work. Thewhile(ss >> tmp)checks, if it actually did work. If the string is empty (I'm not sure with C++ but in C, strings terminate with an invisible character\0), or if the next thing is not a number, then the test fails, and while skips the rest.For the last line we are now in the body of the while loop, so the last character was a number and it got saved into
tmp. As en example, let's say we had"1,2", then now the1is extracted as integer and saved intotmp, and the remaining string in the stream is",2". We can add that number to the vector (result.push_back(tmp);), and due to the structure of the string, which we know, we now expect the next element to be of type character, as it is the,. We need to extract that from the string, because otherwise in the next loop of the while case will try to extracht a number as the next thing of the string, but gets the comma, which cannot be extracted as integer, and therefore the loop condition will fail and we jump out after only the first extracted number.We actually never use
ch, it's just to get rid of all the commas and make the loop work.I hope this helps?
pygospa ... and of course, once the string is empty, extracting a number will fail aswell, so this is how we get all numbers, then exit the loop and return the vector to the calling function (in this case
main()).iamprakashom thanks a lot mate :) well explained. It cleared all of my doubt.
Muthaiah Well Explained. Thanks :-)
mohitgogri04 The best explanation of stringstream till now. thanks a lot!
rohillakriti21 Very well explained. Thanks a lot.
meher_amey23 Thanks a lot, and very nice sexplanation indeed :)
jooookerwang Thank you so much!!You made me clear.
abhijiths148 thanks friend... :)
tliu41 Thanks a lot, this is very helpful
CurlyHurlyGirl very good explanation, thanks
Sneha9594 really helpful. Thanks.
trinadh1729 Thank you, well explained
Purvi97 thankyou literally helped a lot
ItsThwomp WOW THAT HELPED A LOT THANKS BRO
damoliaarvind thanks pygospa........
Anshul_Dadhich You made a perfect hit. Well explained. Special thanks.
NAVEEN14 yes
GaneshJCS Hey, great explanation, that cleared out some stuff, could you please explain why this code fails when the numbers are separated by a space, rather than a comma?
I assume it is because ss thinks the string ended because space is \0. Is that correct?
oms25verma This code works: vector parseInts(string str) { stringstream ss(str); int num; vector numbers; while (ss >> num) { numbers.push_back(num); } return numbers; } in main instead of cin use getline(cin,str);
oms25verma [deleted]
oms25verma may be because space is default delimiter so it does not require ss>>ch(to separate space) which was used in previous case
anandhavallijl Thanks, it teach me a lot
ketantoo Thanks a ton..especially for pointing out why [ch] is used...really helpful.
singhash1234567 Awesome explanation
vipulj11 Awesome explanation ... just had a single doubt though that if I combined and replaced the extraction as
while(ss>>i>>ch)
it does not work.It fails the last time.
Umasou because there is no deliminator at end of the string, for this special case ss>>i>>ch is not True.
zebacsdamu each time you use (ss>>i>>ch) it expects 2 values, which is not always possible. not in the case when the numbers separated by delimeters are odd. Thats why its giving you an error.
meaux [deleted]sigma9K Thanks for explaining so well.
_cipher got proper idea about stringstream :) thank u :)
AnnieRajoria Thank you for the great explanation! Just had a small doubt..how come a number such as 23 is pushed into the vector as 1 number(23) since we push values as soon as we get an integer. Then how come different numbers are distinguished while being oushed into the vector(23 & 8). Thank You
sam_khan U r awesome dude!! Thanks!!
erlandas what a great explanation!
dhakrey199 superb explanation,Thnx
venkatownsdraven thanks a lot
rachna_gupta I tried various sources to understand it but you explained it so much better. Thanks a lot.
manu_mm1997 Thank You very much for explanation
h992110080 Thank you very much!
akshatha_k_holla Thanks a lot .. Really helped me understand stringstream.
Manollas Good explanation.Thanks a lot.
germano_c_lodi basically the best explanation about stringstream on internet
detacher So what does ch get at the last iteration? There is no comma after last integer. How it doesn't throw exception?
ksa_karan97 what would happen if we simply put a statement as stringstream ss; will it throw up an error??
isha2866 Nicely explained. Thank you!
amidsedghi Sick explanation bra! Great job
xslittlegrass This seems to give wrong answer if there is an extrac
,in the input, ie.23,4,56,.
Lazarus94 great explanation bro!
shivamyadav2512 Thanks @pygospa
rahulsahu_blog Thank you, This Helped a lot.
manikanthg Thanks a lot man... Well explained.
_silent_ Thanks man,I searched everythin on internet but i didn't found anything but after is studied that i understood it pretty well
rkimothi Thanks for the explanation!! Very well explained.
anirudhmittal Very lucid explanantion . Thanks!
prateekchaplot Nice! Thanks...
sonupanchal u made my day :) .. and cleared many concepts in just one xplaination .. u r awesome
clover_123 Thanks Bro
yuchengfu2011 I just have one question. If the str contians 0 in it. Dose while will terminate while 0 is assigned to tmp?
Manoaj_Mani Thank u bro:)
techie_aditya int intg; while(scanf("%d,",&intg)!= EOF){ cout << intg << endl; }
ankit_891 Good explaination ! Thanks a lot!!
bhard_puja thank uh so much sir.....i help me a lot...very nice explanation
erayushi39 Thanxx for the wonderful explanation..it really helped
Thirumagaldhivya why we used push back?
sayan_mahapatra1 Awesome Explanation, really cleared all my doubts
hasanakhiar Best explaination about stringstream.. Thanks
tarunchauhan580 vector parseInts(string str) { stringstream ss(str); vector numbers; while (!ss.eof()) { if(ss >> num) numbers.push_back(num); std::cout<
vishnucfc7 I think this one is a perfect solution. Even if the string's first character isn't an integer, it waits for an integer to come and then extracts. Kudos !!
diegon Tried it! The (!ss.eof()) fails to detect the eof for some reason. Can you supply the full code?
ehsan_wwe a tiny way
string a; cin>>a; for (int i=0;i<a.size();i++) { if (a[i]!=',') cout<<a[i]; else cout<<"\n"; }smallduck perfect
guls453 will u explain why we are using ','
Rhys_Goodall his test condition for printing the number is if the ith element is not a comma. if it is a comma he instead ends the line in the output using \n .
learner_codes wow
nice one :)
abdelghanihaker but if the element isn't a comma...
mohitst Wonderful
normanj2 This was my idea for how to write it as well. Much simpler, but I guess it defeats the purpose of the exercise -- to utilize stringstream.
abhishek_satyam1 Awesome. I am impressed.
vishmalviya6 return nhi kr rha
satya_encode This was an obvious method, but the point of the program was to learn the concept of string stream.
itsamitgoel what will the last ch hold??. Example s="23,49". First ch will hold value','. What will the next iteration of ch hold??
nishchayvermani [deleted]
manvik1499 nice explanation... cheers!
saurabhpandey591 Thanks a lot friend. You made it clear in an easy way
rheriel We can also "peek" at the top of the stream and "ignore" if we find a comma, PSB:
stringstream ss(str); int a; vector<int> vec; while (ss >> a){ vec.push_back(a); if (ss.peek() == ','){ ss.ignore(); } } return vec;
I hope this helps!
Regards!
akoushik1999 can you explain me the use of ss.peek()
rheriel You look at the top of the stack, peek doesn't remove the element.
blitzippy Just use ss as the condition for a while loop.
vector<int> parseInts(string str) { vector<int> vec; // Declares a vector to store the ints stringstream ss(str); // Declares a stringstream object to deal with the modification of the string char ch; int temp; while(ss) // While the stringstream object does not hit a null byte { ss>>temp>>ch; // Extract the comma seperated ints with the extraction >> operator vec.push_back(temp); // Push the int onto the vector } return vec; // Return the vector of ints }
jkyadav11404572 i understand this now....nice code with comments
mohya it is not working
sowndharyalaksh1 nice code... i understood well
jutoorsuprajare1 can anyone explain me by taking an example for this
lishantsahu why would it extract 44 and not 4 from array {44,23,45}?
benjodaman Because stringstreams are quite smart objects - when you extract from a ss to an int, it will remove only as much of the stream as can be validly converted to an int.
ulissescruz10 stringstream ss(str); vector<int> v; for(int i=0; ss>>i; ss.ignore()) v.push_back(i) return v
ChinGyi what would happen if a comma is coming first? I really like the code though.
saurabha20 i dont get it how exactly ss.ignore() works in this case as terminating statement for for loop
pat_laugh ss.ignore()ignores the next character (in this case that'd be a comma). It "looks like" doing++i, since ss goes to the next character. I think it's bad coding style.ignore()is actually a function that takes an optional parameter (that defaults to 1) telling how many characters to ignore. It'd be better to writess.ignore(1).Also,
i=0is useless sinceigets assigned right after in the condition sectionss>>i.saurabha20 thanks pat this is good information.
tigerleapgorge [deleted]roman_kiselew Cool! Really cool.
PiCTosi Here's my solution:
#include <iostream> #include <sstream> #include <vector> using namespace std; vector<int> parseInts(const string& str) { vector<int> v; int i; char c; stringstream ss(str); while (ss >> i) { v.push_back(i); ss >> c; } return v; }
By the way, why don't we get well-written functions to work with?
maincould look like:int main() { string str; cin >> str; for (const int& i : parseInts(str)) cout << i << endl; return 0; }
instead of
int main() { string str; cin >> str; vector<int> integers = parseInts(str); for(int i = 0; i < integers.size(); i++) { cout << integers[i] << "\n"; } return 0; }
and notice the signature of
parseIntsavoiding copying the passedstringwhen calling the function and helping the compiler in any optimization! But I've seen way worse in other exercices ...For the lulz:
Although it doesn't respect all the requirements of the exercice (e.g. using
parseInts), here's a 10-liner getting the job done:#include <iostream> #include <string> using namespace std; int main() { string s; cin >> s; for (size_t f = 0; (f = s.find(",", f)) != string::npos; s.replace(f, 1, "\n")); cout << s << endl; return 0; }
and, even better, a 6-liner only using the standard streams
std::cinandstd::cout(nostrings)!#include <iostream> int main() { for (char c; std::cin >> c;) std::cout << (c != ','? c : '\n'); return 0; }
This will be hard to beat ...
jyotindersingh [deleted]lishantsahu why would it extract 44 and not 4 from array {44,23,45}?
gnemlock They are basically going through each character and reprinting it; however, whenever they come to a comma, they instead print a
'\n', creating the new line.cout << (c != ',' ? c : '\n')takes advantage of the ternary operatorx ? y : z, which follows the process of validatingx, and passing backyif it is true, orzif it is not. It basically rewrites"44,23,45"as"44\n23\45".
kandhan3694 There are a lot of easy ways to do but The proper way to implement using stringstream is https://github.com/KandhanSekar/HAckerrank-C--/tree/master/stringstream
shot_adidas works fine! thank you
satya_encode vector<int> parseInts(string str) { stringstream ss; ss << str; //transfer string to stringstream vector<int> result; // create a vector to hold the vector containing numbers char character_stream_dump; // a variable to collect all the characters int number_stream; // variable of type int to collect all the integer values while(ss >> number_stream) // as long as (dump numbers from ss in number_stream) holds true-- 2,5,7 becomes ,5,7 { result.push_back(number_stream); // add the collected number in vector ss >> character_stream_dump; // tranfer the stream of characters (,) to character_stream_dump, which means ,5,7 becomes 5,7 } return result; //returns final vector of numbers }
gnemlock A lot of people rewriting the wheel, here. The example mentions
ss >> a, so do not get confused by all of the people not using the basicss >>method.vector<int> parseInts(string str) { // StringStream to store our string for easy output stringstream ss(str); // Integer for storing the size of our final number array. // We start this at 1, as there is 1 more number than comma. int n = 1; // Character to provide a buffer, when reading. char c; // First, go through the array, and count the commas. // Each comma means another number. for(int i = 0; i < str.size(); i++) if(str[i] == ',') n++; // Now we know how many numbers there are, // create the number array. vector<int> array(n); // For each number in the string, pass it into the array, // and than pass the comma into the character buffer. for(int j = 0; j < n; j++) ss >> array[j] >> c; // Return our completed array. return array; }
lordcheeto I skipped the comma by incrementing the position in the input sequence.
vector<int> parseInts(string str) { stringstream ss(str); vector<int> v; int i; while(ss >> i) { ss.seekg(ss.tellg() + 1); v.push_back(i); } return v; }Any downsides to doing it this way? Performance, memory, edge cases?
Nephe An interesting post on the question, that provide a more stable method than just 'skipping' commas. https://www.fluentcpp.com/2017/04/21/how-to-split-a-string-in-c/
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