First, make an ifstream
:
#include <fstream> std::ifstream infile("thefile.txt");
The two standard methods are:
- Assume that every line consists of two numbers and read token by token:
int a, b; while (infile >> a >> b) { // process pair (a,b) }
- Line-based parsing, using string streams:
#include <sstream> #include <string> std::string line; while (std::getline(infile, line)) { std::istringstream iss(line); int a, b; if (!(iss >> a >> b)) { break; } // error // process pair (a,b) }
You shouldn’t mix (1) and (2), since the token-based parsing doesn’t gobble up newlines, so you may end up with spurious empty lines if you use getline()
after token-based extraction got you to the end of a line already.
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