Facing problem with iterating over vector> and printing data

Question

I am reading a CSV file and storing it in vector vector string. I want to print the data and for that I am using two for loops one iterating over vector of vector and other iterating over the vector string.

a1,b1,c1,d1
a1,b1,c4,d3
a1,b2,c2,d2
a2,b3,c3,d4
a2,b4,c3,d4

this is the CSV data I am reading. Below code I am using to print it to screen

void ReadCSV::printdata(vector<vector<string>> ipd){
    for(auto it1 = ipd.begin();it1 != ipd.end();++it1){
        vector<string> test = *it1;
        for(auto it2 = test.begin();it2 != test.end();++it2){
            string r = "";
            r= *it2;
            cout<<r<<" ";
        }
        cout<<endl;
    }
}

But the output I am getting seems is not iterating properly:

a1 b1 c1 d1 
a1 b1 c1 d1 a1 b1 c4 d3 
a1 b1 c1 d1 a1 b1 c4 d3 a1 b2 c2 d2 
a1 b1 c1 d1 a1 b1 c4 d3 a1 b2 c2 d2 a2 b3 c3 d4 
a1 b1 c1 d1 a1 b1 c4 d3 a1 b2 c2 d2 a2 b3 c3 d4 a2 b4 c3 d4

I used below code to read data:

vector<vector<string>> ReadCSV:: ReadData(){
    fstream fin(filename);
    vector<string> temp;
    string val1, val2, val3 ,val4;
    if(!fin.is_open()){
        cout<<"ERROR: file open";
    }
    cout<<"FIRST OUTPUT: "<<endl;
    while(fin.good()){
        getline(fin, val1,',');
        //store
        temp.push_back(val1);
        cout<<val1<<" ";
        getline(fin, val2,',');
        temp.push_back(val2);
        cout<<val2<<" ";
        getline(fin, val3,',');
        temp.push_back(val3);
        cout<<val3<<" ";
        getline(fin, val4,'\n');
        temp.push_back(val4);
        cout<<val4<<" ";
        csvdata.push_back(temp);
    }
    cout<<endl;
    return csvdata;
}

Can anyone tell where I am going wrong, other issue I face is when I run debugger (ECLIPSE IDE) and hover over a variable it opens up some popup but doesn't displays the value of the variable, such as "string r" in this case. thanks

Are you sure that the error is in the `printdata` function, and not with how you read (or otherwise process) the data? Have you tried to step through the code statement by statement in a debugger while monitoring variables and their values and contents? — Some programmer dude, Oct 19 '19 at 02:01
Agree with @Someprogrammerdude It looks like the error is most likely in the reading that populates `vector>` — doug, Oct 19 '19 at 02:04
Yes I did debugging on reading part, i have updated the reading code in the description — adi_226, Oct 19 '19 at 02:04
Time to do some [rubber duck debugging](https://en.wikipedia.org/wiki/Rubber_duck_debugging) of that reading code. What happens with `temp` when you read the contents of the file? Will `temp` ever be "reset" or cleared? — Some programmer dude, Oct 19 '19 at 02:06
You are simply appending data to temp each time. You need to clear it after each line. — doug, Oct 19 '19 at 02:07
Also please read [Why is iostream::eof inside a loop condition (i.e. `while (!stream.eof())`) considered wrong?](https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-i-e-while-stream-eof-cons) Doing `while (fin.good())` is just the same. — Some programmer dude, Oct 19 '19 at 02:07
Unrelated: `void ReadCSV::printdata(vector> ipd)` should be a oneliner. ... if "`ReadCSV::printdata`" doesn't raise concerns. — Ted Lyngmo, Oct 19 '19 at 02:07
As for how to solve your problem, try to define variables in the closest scope where they are needed. In your case, `temp` and `val1` through `val4` could all be defined inside the loop. — Some programmer dude, Oct 19 '19 at 02:09
@Someprogrammerdude I like your rubber duck debugging suggestion best but I commented before I saw your comment. — doug, Oct 19 '19 at 02:11
@adi_226 Before I answer that - Doesn't the combination `ReadCSV::printdata` look a little bit suspicious? — Ted Lyngmo, Oct 20 '19 at 00:53
@TedLyngmo sorry but I don't understand what you are pointing to. — adi_226, Oct 20 '19 at 00:58
A class named `Read...` and a method named `print...` does look a bit conflicting. — Ted Lyngmo, Oct 20 '19 at 01:06
@adi_226 Something like `void ReadCSV::printdata(const std::vector>& ipd) { std::for_each(ipd.begin(), ipd.end(), [](const auto& v) { std::copy(v.begin(), v.end(), std::ostream_iterator(std::cout, " ")); }); }` should work. — Ted Lyngmo, Oct 20 '19 at 12:38

nae9on · Accepted Answer · 2019-11-02T11:29:47.223

Your CSV reader besides having some minor issues is hard-coded to read exactly 4 comma separated values. Here is a more general code which can read as many lines and with each line having variable number of comma separated values.

#include <iostream>
#include <fstream>
#include <vector>
#include <iterator>
#include <algorithm>

template<typename In, typename Out>
void csv2vec(In first, In last, Out& result) {
    std::string temp;
    unsigned i{0};
    while(1) {
        do{
            if(*first == '\n') break;
            temp.push_back(*first);
            ++first;
        }while(*first != ',' && first != last);
        result[i].push_back(temp);
        if(*first == '\n') {
            ++i;
            result.resize(i+1);
        }
        temp.clear();
        if(first == last) break;
        ++first;
    }
}

int main(void) {
    std::vector<std::vector<std::string>> vec(1);
    std::ifstream in("data.txt");
    std::istreambuf_iterator<char> begin(in);
    std::istreambuf_iterator<char> end;
    csv2vec(begin,end,vec);

    for(const auto& vecouter : vec) {
        for(const auto& elem : vecouter){
            std::cout<<elem<<" ";
        }
        std::cout<<"\n";
    }
   return 0;
}

Note: I have used istreambuf_iterator which never skips any characters (including whitespaces such as '\n'). It grabs whatever's next in the stream buffer unlike istream_iterator which skips whitespaces. Also istream_iterator is useful when performing formatted input and is slower than the istreambuf_iterator. Reference: Item 29, Effective STL, Scott Meyers.

Facing problem with iterating over vector> and printing data

1 Answers1