Такие разные потоки

#include <cassert>
#include <fstream>
#include <iostream>
#include <string>
#include <string_view>
#include <map>
#include <vector>

using namespace std;

string SplitLine(const string &line) {
    if (line.empty()) {
        return "";
    }

    string result;

    for (auto &_char: line) {
        if (_char == '>') {
            continue;
        }
        result += _char;
    }
    return result;

}



void CreateFiles(const string &config_file) {
    ifstream ifs(config_file);

    map<string, vector<string>> splits;
    string name_file;
    if (!ifs.bad()) {
        string line;

        while (getline(ifs, line)) {

            if (line.find(".txt"s) != string::npos) {
                name_file = line;
                splits[line];

            } else {
                splits[name_file].push_back(SplitLine(line));

            }

        }

        ifs.close();
    }


    for(auto &[file, text] : splits) {
        if (!ifs.bad()) {
            ofstream ofs(file);
            for(auto &str : text) {

                if (!ofs.bad())
                {
                    ofs << str<< endl;
                }
            }
            ofs.close();
        }
    }

}

string GetLine(istream &in) {
    string s;
    getline(in, s);
    return s;
}

int main() {
    ofstream("test_config.txt"s) << "a.txt\n"
                                    ">10\n"
                                    ">abc\n"
                                    "b.txt\n"
                                    ">123"sv;


    CreateFiles("test_config.txt"s);
    ifstream in_a("a.txt"s);
    assert(GetLine(in_a) == "10"s && GetLine(in_a) == "abc"s);

    ifstream in_b("b.txt"s);
    assert(GetLine(in_b) == "123"s);
}