编写元组的 C++ 映射并设置为文件

Question

我有一个由元组作为键和集合作为值的无序映射。

我如何将此hash_DICT写入文件？

#include <tuple>
#include <map>
#include <set>

int main() {
   // Create dict here
   map <tuple<int,int,int>,set<int>> hash_DICT;
   for(int i =0; i < 10; i++){
      tuple<int,int,int> tup_key = {i, i, i};
      set<int> set_val = {i};
      hash_DICT[tup_key] = set_val;
   }
   // Write hash_DICT to file here
   return 0;
}

改编自https://www.stev.org/post/cppreadwritestdmaptoafile ：

int WriteFile(std::string fname, std::map<std::tuple<int,int,int>,std::set<int>> *m) {
    int count = 0;
    if (m->empty())
            return 0;

    FILE *fp = fopen(fname.c_str(), "w");
    if (!fp)
            return -errno;

    for(std::map<std::tuple<int,int,int>,std::set<int>>::iterator it = m->begin(); it != m->end(); it++) {
            fprintf(fp, "%s=%s\n", it->first.c_str(), it->second.c_str());
            count++;
    }

    fclose(fp);
    return count;
}

但错误如下：

class "std::tuple<int, int, int>" has no member "c_str"
class "std::set<int, std::less<int>, std::allocator<int>>" has no member "c_str"

我应该如何修改它们才能写入文件并读取它们？

Answer 1

看看错误：

class "std::tuple<int, int, int>" has no member "c_str"
class "std::set<int, std::less<int>, std::allocator<int>>" has no member "c_str"

这些错误是不言自明的c_str()是一个函数，它给出了const char * （或 c 中的字符串），正如您所遵循的教程一样，它们使用了map<std::string, std::string>但您map由不同类型的元素组成。 这些错误现在有意义吗？

更新：当您要求从文件中读取和写入时，这里是完整的解决方案：

---

#include <tuple>
#include <map>
#include <set>
#include <iostream>
#include <fstream>

void read_from_file(const std::string &fileName, std::map<std::tuple<int, int, int>, std::set<int>> &targetMap) {

    std::ifstream myStream(fileName);
    if (!myStream.is_open()) {
        std::cout << "Error opening file" << std::endl;
        return;
    }

    int a, b, c, set_size;
    while (myStream >> a >> b >> c >> set_size) {
        std::tuple<int, int, int> tuple(a, b, c);
        std::set<int> set;

        for (int i = 0; i < set_size; i++) {
            int val;
            myStream >> val;
            set.insert(val);
        }
        targetMap[tuple] = set;
    }
}

void write_to_file(const std::string &fileName, const std::map<std::tuple<int, int, int>, std::set<int>> &sourceMap) {
    std::ofstream myFile(fileName);
    if (!myFile.is_open()) {
        std::cout << "Failed to open file" << std::endl;
        return;
    }

    for (const auto &it:sourceMap) {
        myFile << std::get<0>(it.first) << " " << std::get<1>(it.first) << " " << std::get<2>(it.first) << " ";
        myFile << it.second.size()
               << " "; // i'll be easier to set values read from file.. otherwise we need to use stringstream
        for (const auto &it1: it.second) {
            myFile << it1 << " ";
        }
        myFile << std::endl;
    }
    myFile.flush();
}


int main() {
    // Create dict here
    std::map<std::tuple<int, int, int>, std::set<int>> sourceMap;
    for (int i = 0; i < 10; i++) {
        std::tuple<int, int, int> tup_key = {i, i, i};
        std::set<int> set_val = {i};
        sourceMap[tup_key] = set_val;
    }

    write_to_file("file_1.txt", sourceMap);

    // now let's read it..
    sourceMap.clear();
    read_from_file("file_1.txt", sourceMap);

    for (const auto &it:sourceMap) {
        std::cout << std::get<0>(it.first) << " " << std::get<1>(it.first) << " " << std::get<2>(it.first) << " ";
        std::cout << it.second.size() << " ";
        // it'll be easier to set values read from file.. otherwise we need to use stringstream
        for (const auto &it1: it.second) {
            std::cout << it1 << " ";
        }
        std::cout << std::endl;
    }

    return 0;
}

您可以非常轻松地使用ofstream写入文件并访问正确的成员：

#include <tuple>
#include <map>
#include <set>
#include <iostream>
#include <fstream>

int main() {
    // Create dict here
    std::map<std::tuple<int, int, int>, std::set<int>> hash_DICT;
    for (int i = 0; i < 10; i++) {
        std::tuple<int, int, int> tup_key = {i, i, i};
        std::set<int> set_val = {i};
        hash_DICT[tup_key] = set_val;
    }

    std::ofstream myfile;
    myfile.open("output.txt");

    if (!myfile.is_open()) {
        std::cout << "Failed to open file" << std::endl;
        return 0;
    }

    for (const auto &it:hash_DICT) {
        myfile << std::get<0>(it.first) << " " << std::get<1>(it.first) << " " << std::get<2>(it.first) << " --> ";
        for (const auto &it1: it.second) {
            myfile << it1 << " ";
        }
        myfile << std::endl;
    }

    myfile.flush();

    return 0;
}