I'm having a bit of trouble with a school assignment for C++. The specific problem I'm having involves reading lines from a file that contain a series of between 5 and 6 grades. The grades for each student appear together in a single line following the student's name and id number. The challenge here is that the grades can have a variable number of spaces between them, and that if there are only 5 grades present, an error message needs to be generated to screen but the program is to continue running and average the 5 grades. Example of input: 23 46 68 85 98
I got the student name and id easily, but the string of digits is giving me problems. My plan was to getline and then tokenize the string and assign each token to a cell in an array. This works fine for 6 grades, but when only 5 grades are present it is assigning garbage to the sixth cell.
Here is the snippet of code that concerns this section:
fin.getline(gradeList, 200);
grade = strtok (gradeList, " ");
while (grade != '\0')
{
gradeArr[cycler] = atoi(grade);
grade = strtok(NULL, " ");
cycler++;
}
I tried doing an isdigit check on each token before converting it to an int, and writing a 0 in for any token that failed the isdigit check, but that didn't work at all. It seems like it is pulling the name from the next line when only 5 grades are present and then when it atoi's it, it changes it to a huge number.
I thought that when the program did getline, it would only grab the line until it saw the endline terminator. Is this not what is happening?
Scrap the C nonsense and use real C++:
#include <string>
#include <sstream>
#include <fstream>
#include <vector>
// ...
std::vector<int> grades;
std::string line;
while (std::getline(fin, line))
{
std::istringstream iss(line);
int grade;
while (iss >> grade)
{
grades.push_back(grade);
}
}
Here's a somewhat more compact and elegant method, using istream-iterators and back-inserters:
#include <iterator>
#include <algorithm>
// other headers as before
std::vector<int> grades;
for (std::string line; std::getline(fin, line); )
{
std::istringstream iss(line);
std::copy(std::istream_iterator<int>(iss), std::istream_iterator<int>(),
std::back_inserter(grades));
}
The point is that formatted token extraction (>>) from streams does already precisely what you want to, and it subsumes both tokenizing and parsing into integers.
The istream_iterator encapsulates the token extraction and allows you to treat a stream as if it were already a sequence of parsed tokens. The copy algorithm then simply copies this sequence into a vector, inserting it at the end of the container.
If you use strtol or strtod, it gives you back a pointer to the end of what you just processed, so you can continue from there. No tokenization necessary :)
But it sounds like your problem is that you're reading the wrong line. Print out the gradeList variable before you start parsing.
You should end up with something like this:
fin.getline(grade_text, 200);
const char* grade = grade_text;
const char* next_grade;
double grade_sum = 0;
for( int grade_count = 0; grades[grade_count] = strtol(grade, &next_grade, 10), next_grade > grade; ++grade_count )
grade_sum += grades[grade_count];
double mean_grade = grade_sum / grade_count;
Related
I am a young programmer who is trying to learn c++. i have a working csv.file. but i want to search for a specific number assigned to the name and then displays the name of what i'm looking for. i have the file here:
1,Bulbasaur,grass
2,Ivysaur, grass
3,Venusaur, grass
4,Charmander, fire
5,Charmeleon, fire
6,Charizard, fire
7,Squirtle, water
8,Wartortle, water
9,Blastoise, water
Code
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ifstream ip("pokedex.csv");
string pokedexnum[9];
string pokemonName[9];
string pokemonType[9];
cout<<"please enter a pokemon number:"<<" ";
cin>>pokemonType[0];
while (ip.good()){
getline( ip, pokedexnum[0]);
getline( ip, pokemonName[0]);
getline( ip, pokemonType[0]);
}
cout<<"the pokemon that is:"<< " "<<pokedexnum[0]<< "is the pokemon called:"<< pokemonName[0];
ifstream close("pokedex.csv");
return 0;
}
when it runs
please enter a pokemon number: 1
the pokemon that is: is the pokemon called:8,Wartortle, water
could you please point out what i am doing wrong?
Among the issues in this code:
You're not using std::getline correctly for comma-separated data. The result is each pass is consuming three lines from your input file; not three values from each line.
You're also not using ip.good() correctly as a while-condition.
You're retaining your test value in the array, which will be overwritten on the first iteration pass, so it is lost.
You're ignoring potential IO failures with each std::getline invoke.
You're overwriting slot-0 in your arrays with each loop iteration.
Minor, ifstream close("pokedex.csv"); clearly isn't doing what you think it is. That just creates another fstream object called close on the given file name.
The later may be intentional for now, but clearly broken in the near future.
In reality, you don't need arrays for any of this. All you're doing is reading lines, and seem to want to test the input number against that of the CSV data first column, reporting the line that you find, then ending this.
So do that:
Read the input value to search for.
Open the file for scanning.
Enumerate the file one line at a time.
For each line from (3), use a string stream to break the line into the comma separated values.
Test the id value against the input from (1). If the same, report the result and break the loop; you're done.
The result is something like this:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <cstdlib>
int main()
{
std::cout<<"please enter a pokemon number: ";
long num;
if (std::cin >> num && num > 0)
{
std::ifstream ip("pokedex.csv");
std::string line;
while (std::getline(ip, line))
{
std::istringstream iss(line);
std::string id, name, skill;
if (std::getline(iss, id, ',') &&
std::getline(iss, name, ',') &&
std::getline(iss, skill))
{
char *endp = nullptr;
long n = std::strtol(id.c_str(), &endp, 10);
if (id.c_str() != endp && n == num)
{
std::cout << "The pokemon that is: " << num << " is called: " << name << '\n';
break;
}
}
}
}
}
Admittedly untested, but it should work.
Whether you want to store the items in arrays at this point is entirely up to you, but it isn't needed to solve the somewhat abstract problem you seem to be attempting, namely finding the matching line and reporting the name from said-same. If you still want to store them in arrays, I suggest you craft a structure to do so, something like:
struct Pokemon
{
int id;
std::string name;
std::string skill;
};
and have a single array of those, rather than three arbitrary arrays that must be kept in sync.
Four issues jump out at me:
You store the user's input into pokemonType, but then also use pokemonType for reading data from your CSV file. The file input is going to overwrite the user input.
Your file input loop always references index 0. All of the lines from your data file are going into element 0. That's the main reason that even if the user inputs 1, the output is from the last line of the data file.
Your file reading loop is structured like you want to put one part of each data line into a different array, but what you've written actually reads three lines on every iteration, storing those lines into the three different arrays.
This isn't affecting your output, but the code ifstream close("pokedex.csv"); is written like you want to close the file stream you opened, but I do believe what this line actually does is create a new ifstream called close, and opens pokedex.csv attached to it. In other words, it's just like your other line ifstream ip("pokedex.csv"); but with close as the variable name instead of ip.
You are going to want to look into something called "string tokenization". Start with some web searches, apply what you read about to your code, and of course if you hit another snag, post a new question here to Stack Overflow, showing (as you did here) what you tried and in what way it isn't working.
Elaborating on #3, here's what how your data file is being read:
at the end of the 1st iteration of the file-reading loop, ...
pokedexnum[0] is "1,Bulbasaur,grass"
pokemonName[0] is "2,Ivysaur, grass"
pokemonType[0] is "3,Venusaur, grass"
at the end of the 2nd iteration of the file-reading loop, ...
pokedexnum[0] is "4,Charmander, fire"
pokemonName[0] is "5,Charmeleon, fire"
pokemonType[0] is "6,Charizard, fire"
at the end of the 3rd iteration of the file-reading loop, ...
pokedexnum[0] is "7,Squirtle, water"
pokemonName[0] is "8,Wartortle, water"
pokemonType[0] is "9,Blastoise, water"
And that's why
<< "is the pokemon called:"<< pokemonName[0];
outputs
is the pokemon called:8,Wartortle, water
This question already has answers here:
Why does reading a record struct fields from std::istream fail, and how can I fix it?
(9 answers)
Closed 6 years ago.
I was wondering how to store data from a CSV file into a structured array. I realize I need to use getline and such and so far I have come up with this code:
This is my struct:
struct csvData //creating a structure
{
string username; //creating a vector of strings called username
float gpa; //creating a vector of floats called gpa
int age; //creating a vector of ints called age
};
This is my data reader and the part that stores the data:
csvData arrayData[10];
string data;
ifstream infile; //creating object with ifstream
infile.open("datafile.csv"); //opening file
if (infile.is_open()) //error check
int i=0;
while(getline(infile, data));
{
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
i++;
}
Further, this is how I was attempting to print out the information:
for (int z = 0; z<10; z++)
{
cout<<arrayData[z].username<<arrayData[z].gpa<<arrayData[z].age<<endl;
}
However, when running this command, I get a cout of what seem to be random numbers:
1.83751e-0383 03 4.2039e-0453 1.8368e-0383 07011688
I assume this has to be the array running not storing the variables correctly and thus I am reading out random memory slots, however, I am unsure.
Lastly, here is the CSV file I am attempting to read.
username,gpa,age
Steven,3.2,20
Will,3.4,19
Ryan,3.6,19
Tom,3,19
There's nothing in your parsing code that actually attempts to parse the single line into the individual fields:
while(getline(infile, data));
{
This correctly reads a single line from the input file into the data string.
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
You need to try to explain to your rubber duck how this is supposed to take a single line of comma-separated values, like the one you showed in your question:
Steven,3.2,20
and separate that string into the individual values, by commas. There's nothing about the >> operator that will do this. operator>> separates input using whitespaces, not commas. Your suspicions were correct, you were not parsing the input correctly.
This is a task that you have to do yourself. I am presuming that you would like, as a learning experience, or as a homework assignment, to do this yourself, manually. Well, then, do it yourself. You have the a single line in data. Use any number of tools that C++ gives you: the std::string's find() method, or std::find() from <algorithm>, to find each comma in the data string, then extract each individual portion of the string that's between each comma. Then, you still need to convert the two numeric fields into the appropriate datatypes. And that's when you put each one of them into a std::istringstream, and use operator>> to convert them to numeric types.
But, having said all that, there's an alternative dirty trick, to solve this problem quickly. Recall that the original line in data contains
Steven,3.2,20
All you have to do is replace the commas with spaces, turning it into:
Steven 3.2 20
Replacing commas with spaces is trivial with std::replace(), or with a small loop. Then, you can stuff the result into a std::istringstream, and use operator>> to extract the individual whitespace-delimited values into the discrete variables, using the code that you've already written.
Just a small word of warning: if this was indeed your homework assignment, to write code to manually parse and extract comma-delimited values, it's not guaranteed that your instructor will give you the full grade for taking the dirty-trick approach...
UNDER CONSTRUCTION
Ton, nice try and nice complete question. Here is the answer:
1) You have a semicolon after the loop:
while(getline(infile, data));
delete it.
How did I figure that out easily? I compiled with all the warnings enabled, like this:
C02QT2UBFVH6-lm:~ gsamaras$ g++ -Wall main.cpp
main.cpp:24:33: warning: while loop has empty body [-Wempty-body]
while(getline(infile, data));
^
main.cpp:24:33: note: put the semicolon on a separate line to silence this warning
1 warning generated.
In fact, you should get that warning without -Wall as well, but get into using it, it will also make good to you! :)
2) Then, you read some elements, but not 10, so why do you print 10? Print as many as the ones you actually read, i.e. i.
When you try to print all 10 elements of your array, you print elements that are not initialized, since you didn't initialize your array of structs.
Moreover, the number of lines in datafile.csv was less than 10. So you started populating your array, but you stopped, when the file didn't have more lines. As a result, some of the elements of your array (the last 6 elements) remained uninitialized.
Printing uninitialized data, causes Undefined Behavior, that's why you see garbage values.
3) Also this:
if (infile.is_open()) //error check
could be written like this:
if (!infile.is_open())
cerr << "Error Message by Mr. Tom\n";
Putting them all together:
WILL STILL NOT WORK, BECAUSE ss >> arrayData[i].username; eats the entire input line and the next two extractions fail, as Pete Becker said, but I leave it here, so that others won't make the same attempt!!!!!!!
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;
struct csvData //creating a structure
{
string username; //creating a vector of strings called username
float gpa; //creating a vector of floats called gpa
int age; //creating a vector of ints called age
};
int main()
{
csvData arrayData[10];
string data;
ifstream infile; //creating object with ifstream
infile.open("datafile.csv"); //opening file
if (!infile.is_open()) { cerr << "File is not opened..\n"; }
int i=0;
while(getline(infile, data))
{
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
i++;
}
for (int z = 0; z< i; z++)
{
cout<<arrayData[z].username<<arrayData[z].gpa<<arrayData[z].age<<endl;
}
return 0;
}
Output:
C02QT2UBFVH6-lm:~ gsamaras$ g++ -Wall main.cpp
C02QT2UBFVH6-lm:~ gsamaras$ ./a.out
username,gpa,age00
Steven,3.2,2000
Will,3.4,1900
Ryan,3.6,1900
Tom,3,1900
But wait a minute, so now it works, but why this:
while(getline(infile, data));
{
...
}
didn't?
Because, putting a semicolon after a loop is equivalent to this:
while()
{
;
}
because as you probably already know loops with only one line as a body do not require curly brackets.
And what happened to what I thought it was the body of the loop (i.e. the part were you use std::stringstream)?
It got executed! But only once!.
You see, a pair of curly brackets alone means something, it's an anonymous scope/block.
So this:
{
stringstream ss(data);
ss >> arrayData[i].username;
ss >> arrayData[i].gpa;
ss >> arrayData[i].age;
i++;
}
functioned on its one, without being part of the while loop, as you intended too!
Any why did it work?! Because you had declared i before the loop! ;)
I want to delete some words from a string but my code doesn't work . I don't have any errors or warnings , but I'm thinking that my string becomes empty. Could someone help me with this? I tried to convert my initial strings into 2 vectors, so that I can navigate more easily then
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string s("Somewhere down the road");
string t("down");
istringstream iss(s);
vector <string> plm;
vector <string> plm2;
do
{
string sub;
iss >> sub;
plm.push_back(sub);
} while (iss);
for(unsigned int i=0 ; i<plm.size();i++){
cout<<plm[i];}
istringstream ist(t);
do
{
string subb;
ist >> subb;
plm2.push_back(subb);
} while (ist);
for(int i=0;i<plm.size();i++){
for(int j=0;j<plm2.size();i++){
{if (plm[i]==plm2[j])
plm.erase(plm.begin()+j);}}}
for(int i=0 ; i<plm.size();i++)
cout<<plm[i];
}
Warning: this is really just a comment that's too long to fit in a comment field. Oh, and a bit of a rant at that.
I'm sure glad we have these modern languages to make life so much easier than it was decades ago. Consider, for example, what this job looked like an the long-since moribund SNOBOL 4 programming language:
s = 'somewhere down the road'
del s 'down' = :s(del)
OUTPUT = s
God, it's nice that we've since made so much progress that we don't have to deal with 3 whole lines of code, and we can now do the job with only 52 lines instead (oh, except that the 52 lines don't actually work, but let's ignore that for the moment).
I guess, in fairness, we can do the job a little more compactly in C++ though. One obvious way would be with std::remove_copy, some stream iterators, and a stringstream or two:
std::istringstream input("somewhere down the road");
std::string del_str("down");
std::istream_iterator<std::string> in(input), end;
std::ostringstream result;
std::remove_copy(in, end, std::ostream_iterator<std::string>(result, " "), del_str);
std::cout << result.str();
There is no benefit in converting to vector - string itself already provides all that is necessary for what you want to do. Anyway, do it this way:
vector<char> v;
v.assign(s.c_str(), s.c_str() + s.length()); // without...
v.assign(s.c_str(), s.c_str() + s.length() + ); // including...
// ... terminating null character
Now it gets easy:
size_t pos = s.find(t);
if(pos != string::npos)
{
s.erase(pos, t.length());
}
This does not care, however, about leaving multiple whitespace or if t is not an entire word within s (e. g. t = "down"; s = "I'm going to downtown."; would result in s == "I'm going to town."), but you did not do so either...
First problem is, if std::string::erase is called only with the beginning position, it erases everything until the end of string.
Second problem is, that the code will just erase all letters which are in the second string, one by one. I.e. not the entire word - for that, you would need to check if the entire word matches, and only then erase (the entire length of the word). Ask yourself - what will happen in the code, if e.g. the first two letters will match, but not the rest of the word?
In your second for loop you never incremented j and inside the if (plm[i]==plm2[j]) block you used j instead of i as your offset in erase().
for(int i=0;i<plm.size();i++)
{
for(int j=0;j<plm2.size();j++)//here you need to increment j
{
if (plm[i]==plm2[j])
plm.erase(plm.begin()+i);//here the offset should be i
}
}
Another thing don't use a do...while loop to read from the stringstream and push back on the vector. If the reading fails you will be pushing invalid data to the vector, instead try something like:
string sub;
while(iss >> sub;)
plm.push_back(sub);//only if reading is successful
...//do the same for the other istringstream too
You do not increment j this is the first thing I saw on your code. Write it correctly then if it still doesnt work, then ask!
Hey guys so I have an assignment for class where I have to split a string and manipulate it. However, when I try to split the string and assign it to an array only the first element comes and the other two don't. Please help.
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
using namespace std;
int main()
{
string str;
cout<<"Enter a first name, middle initial, last name: ";
cin>> str;
string word;
string array[3];
stringstream stream(str);
int counter = 0;
while( getline(stream, word, ' ') )
{
cout<<word;
array[counter] = word;
counter++;
}
cout<<"The "<<array[0].length()<<" characters of the first name are: "<<array[0]<<endl;
cout<<"The "<<array[2].length()<<" characters of the last name are: "<<array[2]<<endl;
string newstring = array[2]+", "+array[0]+" "+array[1];
cout<<"In the phone book, the name would be: "<<newstring<<endl;
cout<<"The length of the name is: "<<newstring.length()<<endl;
cout<<"The comma is at position: "<<newstring.find(",")<<endl;
array[0].swap(array[2]);
cout<<"After the swap, the last name is "<<array[2]<<" and the first name is "<<array[0];
system("pause");
return 0;
}
There are a few blatant errors in your code:
You need to always check your input after trying to read! You do that using the while-loop but you also need to verify that you actually successfully read the string first.
It seems you are mixing the what the input operator for std::string and std::getline() are doing: the input operator reads the first word after skipping leading spaces while std::getline() read, well, a line (whether the line terminator can be specified as third argument).
When reading fixed sized array you always need to make sure you do not read more than fits into this array! You may have heart about hackers exploiting software by using buffer overruns: assuming you'd actually indeed read a line first followed by splitting it into words you'd have created one of those exploitable programs! If you don't want to check before each word if there is enough space in the array, you'd use, e.g., a std::vector<std::string> (doing so also has a problem with hackers, namely that it opens up the program for a Denial of Service attack but although this is still a problem it is a somewhat lesser problem).
There are also a few smaller issues with your program, too:
If you are only reading from a string stream, you should use std::istringstream as there is no need to also set up the writing part of the std::stringstream.
The programs asks for "first name, middle name, and last name". I would read that specification to use, e.g., "John, F., Kennedy" but it seems you'd expect "John F. Kennedy". One reason I would expect that commas are to be used is that I don't have a middle name, i.e., I would enter "Dietmar, , Kühl".
I have the following code that read input from txt file as follow
Paris,Juli,5,3,6
Paris,John,24,2
Canberra,John,4,3
London,Mary,29,4,1,2
my code is to load the data into map then I want to print the map content to make sure that it has been inserted correctly, I check the vaue of m as it is used during splitting the line. However, during the execution I get this as continues 0s which means it is never enter the while loop. I have used this part of code before and it works. I could not find where I've made the mistake.
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <vector>
#include<map>
using namespace std;
struct info {
string Name;
int places;// i will use the binary value to identfy the visited places example 29 is 100101
// this means he visited three places (London,LA,Rome)
vector<int> times; // will represent the visiting time,e.g. 1,2,5 means london 1 time, LA
// twice and Rome five times
};
map<string,vector<info> > log;
map<string,vector<info> >::iterator i;
fstream out;
int main() {
out.open("log.txt", std::ios::in | std::ios::out | std::ios::app);
string line;
char* pt;
string temp[19];
// for each line in the file
while (!out.eof())
{
getline(out,line);//read line from the file
pt=strtok(&line[0],"," );//split the line
int m=0;
while (pt != NULL)
{
temp[m++] = pt; // save the line info to the array
cout<<m<<" ";
pt = strtok (NULL, ",");
}
cout<<m<<" "; // during the execution I get this as continues 0s which means it is never enter the while loop
info tmp;
// read the other data
tmp.Name=temp[1];
tmp.places=atoi(temp[2].c_str());
for ( int i=3;i<=m;i++)
{
tmp.times.push_back(atoi(temp[i].c_str()));
}
// create a new object
log[temp[0]].push_back(tmp);
}
vector<int>::iterator j;
for(i=log.begin();i!=log.end();i++) {
cout<< "From "<< i->first<<" city people who travels: "<<endl;
for (size_t tt = 0; tt < (i->second).size(); tt++) {
cout<< (i->second[tt]).Name<< " went to distnations "<< (i->second)[tt].places<<" \nwith the folloing number of visiting time ";
for (j=((i->second[tt]).times).begin();j!= ((i->second[tt]).times).end();j++)
cout<<*j<<" ";
}
}
system("PAUSE");
return 0;
}
This is an error
// for each line in the file
while (!out.eof())
{
getline(out,line);//read line from the file
should be
// for each line in the file
while (getline(out,line))
{
I find it frankly incredible how often this error is repeated. eof does not do what you think it does. It tests if the last read failed because of end of file. You are using it to try and predict whether the next read will fail. It simply doesn't work like that.
This line is an error
pt=strtok(&line[0],"," );//split the line
strtok works on C strings, there's no guarantee it will work on std::string.
But neither of these are likely to be your real error. I would suggest opening the file with ios::in only. After all you only want to read from it.
Your fstream should not open in app mode. That will seek the file to the end of file. Delete std::ios::app from it.
You can't tokenize an std::string using strtok. Use getline instead:
std::string str("some,comma,separated,data");
std::string token;
while (getline(str, token, ',')) {
cout << "Token: " << token << end;
}
At each iteration, token contains the next parsed token from str.
This is wrong temp[m++] = pt; // save the line info to the array
Switch to something like this, instead of "temp"
std::vector<std::string> vTemp;
pt=strtok(&line[0],"," );//split the line
while (pt != NULL)
{
vTemp.push_back(pt); // save the line info to the array
pt = strtok (NULL, ",");
}
Also consider using something like this to do the split.
std::vector<std::string> SplitString(const std::string &strInput, char cDelimiter)
{
std::vector<std::string> vRetValue;
std::stringstream ss(strInput);
string strItem;
while(std::getline(ss, strItem, cDelimiter))
{
// Skip Empty
if(strItem.size()==0)
continue;
vRetValue.push_back(strItem);
}
return vRetValue;
}
#halfelf really great solution for my simple error, it works but the problem is now when I print the data I got this
From Paris city people who travels:
Juli went to distnations 5
with the folloing number of visiting time 3 6 0
John went to distnations 24
with the folloing number of visiting time 2 6
From Canberra city people who travels:
Johnwent to distnations 4
with the folloing number of visiting time 3 6
From London city people who travels:
Mary went to distnations 29
with the folloing number of visiting time 4 1 2 0
This is not correct as 6 is added to John from Canberra and Paris and 0 is added to Juli and Mary.
any idea of where I get it wrong ,, its about the times vector , its seems that I need to reset the value for each line or clear the content after the insertion. what about the extra 0?