c++ readfile with varying element amounts per line? - c++

Question

if I have a file like this, say called file.txt
20
25 97
97 5
How would i properly read it given that the second column has missing the second element in the first row?I attempted this
int main()
{
ifstream readFile;
string filename;
cout << "Please enter file name and extention: " << endl;
cin >> filename;
readFile.open(filename);
int row = 0;
int column = 0;
while (readFile >> row >> column)
{
//does something
}
However I get segmenation fault

Answer 1

I would like using std::getline to read lines and std::stringstream to parse the lines.
#include <iostream>
#include <fstream>
#include <sstream>
int main(void) {
std::string filename;
std::string line;
std::ifstream readFile;
std::cout << "Please enter file name and extention: " << std::endl;
std::cin >> filename;
readFile.open(filename);
if (!readFile) {
std::cout << "open error\n";
return 1;
}
while (std::getline(readFile, line)) {
std::stringstream ss(line);
int row = 0, column = 0;
if (ss >> row >> column) {
std::cout << "row = " << row << ", column = " << column << '\n';
} else {
std::cout << "invalid line\n";
}
}
readFile.close();
return 0;
}
Another version (also print partial line):
#include <iostream>
#include <fstream>
#include <sstream>
int main(void) {
std::string filename;
std::string line;
std::ifstream readFile;
std::cout << "Please enter file name and extention: " << std::endl;
std::cin >> filename;
readFile.open(filename);
if (!readFile) {
std::cout << "open error\n";
return 1;
}
while (std::getline(readFile, line)) {
std::stringstream ss(line);
int row = 0, column = 0;
bool row_valid = false, column_valid = false;
if (ss >> row) row_valid = true;
if (ss >> column) column_valid = true;
std::cout << "row = ";
if (row_valid) std::cout << row; else std::cout << "(none)";
std::cout << ", column = ";
if (column_valid) std::cout << column; else std::cout << "(none)";
std::cout << '\n';
}
readFile.close();
return 0;
}
Yet another version (support lines with 3 integers and more):
#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
int main(void) {
std::string filename;
std::string line;
std::ifstream readFile;
std::cout << "Please enter file name and extention: " << std::endl;
std::cin >> filename;
readFile.open(filename);
if (!readFile) {
std::cout << "open error\n";
return 1;
}
while (std::getline(readFile, line)) {
std::stringstream ss(line);
std::vector<int> lineInts;
int data;
while (ss >> data) lineInts.push_back(data);
std::cout << lineInts.size() << " elements:";
for (int d : lineInts) std::cout << ' ' << d;
std::cout << '\n';
}
readFile.close();
return 0;
}