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Reading and writing files

Read project files with std::ifstream; write temporary files under /tmp with std::ofstream.

Runs in Zerethon IDE · C++ (GCC 14) Official C++ documentation ↗
main.cpp 
#include <fstream>
#include <iostream>
#include <string>

int main() {
    std::ifstream in("data.csv");
    if (!in) {
        std::cerr << "cannot open data.csv\n";
        return 1;
    }
    std::string line;
    std::getline(in, line);   // header
    int rows = 0;
    while (std::getline(in, line)) {
        std::cout << line.substr(0, line.find(',')) << '\n';
        ++rows;
    }

    std::ofstream("/tmp/report.txt") << "rows=" << rows << '\n';
    std::ifstream report("/tmp/report.txt");
    std::getline(report, line);
    std::cout << line << '\n';
}
data.csv 
name,score
ada,90
alan,85

Output

ada
alan
rows=2
  • Check the stream (if (!in)) — opening a missing file does not throw.
  • Paths are relative to the project root. Project files are read-only; write to /tmp.

Related topics

Official references