How to read-write into/from text file with comma separated values

Question

How do I read data from a file if my file is like this with comma separated values

1, 2, 3, 4, 5\n 6, 7, 8, 9, 10\n \n 

and after reading the file, I want to write the data back into other file as same format above.

I can get total number of lines, using

string line; while(!file.eof()){       getline(file,line);       numlines++;     }     numline--; // remove the last empty line 

but how can I know total number of digits in a row/line ??

I also have vector of ints to store the data. So, I want to read the first line and then count total number of elements in that line, here 5 (1,2,3,4,5) and store them in array/vector, and read next line and store them in vector again and so on till I reach EOF.

Then, I want to write the data to file, again, I guess this will do the job of writing data to file,

numOfCols=1; for(int i = 0; i < vector.size(); i++) {     file << vector.at(i);     if((numOfCols<5) file << ",";//print comma (,)     if((i+1)%5==0)     {                   file << endl;//print newline after 5th value                   numOfCols=1;//start from column 1 again, for the next line     }     numOfCols++; } file << endl;// last new line 

So, my main problem is how to read the data from file with comma separated values ??

Thanks

Answer 1

Step 1: Don't do this:

while(!file.eof()) {     getline(file,line);     numlines++; } numline--;  

The EOF is not true until you try and read past it. The standard pattern is:

while(getline(file,line)) {     ++numline; } 

Also note that std::getline() can optionally take a third parameter. This is the character to break on. By default this is the line terminator but you can specify a comma.

while(getline(file,line)) {     std::stringstream   linestream(line);     std::string         value;      while(getline(linestream,value,','))     {         std::cout << "Value(" << value << ")\n";     }     std::cout << "Line Finished" << std::endl;  } 

If you store all the values in a single vector then print them out using a fixed width. Then I would do something like this.

struct LineWriter {         LineWriter(std::ostream& str,int size)                 :m_str(str)                 ,m_size(size)                 ,m_current(0)         {}          // The std::copy() does assignement to an iterator.         // This looks like this  (*result) = <value>;         // So overide the operator * and the operator = to         LineWriter& operator*() {return *this;}            void operator=(int val)         {                 ++m_current;                 m_str << val << (((m_current % m_size) == 0)?"\n":",");         }          // std::copy() increments the iterator. But this is not usfull here         // so just implement too empty methods to handle the increment.         void operator++()       {}         void operator++(int)    {}          // Local data.         std::ostream&           m_str;         int const               m_size;         int                     m_current; };  void printCommaSepFixedSizeLinesFromVector(std::vector const& data,int linesize) {     std::copy(data.begin(),data.end(),LineWriter(std::cout,linesize)); } 

Answer 2

here I m posting the code for CSV read as well as write code. I have checked its working fine.

#include <iostream> #include <fstream> #include <sstream> #include <vector> using namespace std;  void readCSV(istream &input, vector< vector<string> > &output) {    string csvLine;     // read every line from the stream     while( getline(input, csvLine) )     {             istringstream csvStream(csvLine);            vector<string> csvColumn;             string csvElement;             // read every element from the line that is seperated by commas             // and put it into the vector or strings             while( getline(csvStream, csvElement, ',') )             {                     csvColumn.push_back(csvElement);             }             output.push_back(csvColumn);     } }  int main() {     ofstream myfile;     string a;     fstream file("b.csv", ios::in);     myfile.open ("ab.csv");     if(!file.is_open())     {            cout << "File not found!\n";             return 1;     }     // typedef to save typing for the following object     typedef vector< vector<string> > csvVector;     csvVector csvData;      readCSV(file, csvData);     // print out read data to prove reading worked     for(csvVector::iterator i = csvData.begin(); i != csvData.end(); ++i)     {             for(vector<string>::iterator j = i->begin(); j != i->end(); ++j)             {           a=*j;                   cout << a << " ";           myfile <<a<<",";   }  myfile <<"\n";  cout << "\n";  }  myfile.close();  system("pause");  }