I'm trying to complete an exercise to write a program that takes the following command line arguments: an input file, an output file, and an unspecified number of words. The program is to read the contents of the input file line by line, find for each word given which lines contain the word, and print the lines with their line number to the output file. Here's my code:

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;

int main(int argc, char* argv[]) {
    if (argc < 4) {
        cerr << "Error #1: not enough arguments provided\n";
        return 1;
    }
    ifstream in(argv[1]);
    if (!in.is_open()) {
        cerr << "Error #2: input file could not be opened\n";
        return 2;
    }
    ofstream out(argv[2]);
    if (!out.is_open()) {
        cerr << "Error #3: output file could not be opened\n";
        return 3;
    }
    ostringstream oss;
    for (int i = 3; i < argc; ++i) {
        int k = 0;
        string temp;
        oss << argv[i] << ":\n\n";
        while (getline(in, temp)) {
            ++k;
            unsigned x = temp.find(argv[i]);
            if (x != string::npos)
                oss << "Line #" << k << ": " << temp << endl;
        }
    }
    string copy = oss.str();
    out << copy;
    in.close();
    out.close();
    return 0;
}

If I try to run that, I get the predicted output for the first word given, but any words following it aren't found. For example, for the source code above will give the following output:

in:

Line #1: #include <iostream>
Line #2: #include <fstream>
Line #3: #include <string>
Line #4: #include <sstream>
Line #5: using namespace std;
Line #7: int main(int argc, char* argv[]) {
Line #12:     ifstream in(argv[1]);
Line #13:     if (!in.is_open()) {
Line #14:         cerr << "Error #2: input file could not be opened\n";
Line #22:     ostringstream oss;
Line #23:     string temp;
Line #24:     for (int i = 3; i < argc; ++i) {
Line #26:         int k = 0;
Line #28:         while (getline(in, temp)) {
Line #30:             unsigned x = temp.find(argv[i]);
Line #31:             if (x != string::npos)
Line #32:                 oss << "Line #" << k << ": " << temp << endl;
Line #35:     string copy = oss.str();
Line #37:     in.close();
out:

That is, it'll find all the instances of the first word given but not any following. What am I doing wrong here?