Question

这是我的有效代码：

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

istringstream* get_line() {
  string line;
  getline(cin, line);
  return new istringstream(line);
}

int main() {
  istringstream* line = get_line();
  int number_of_arrays, number_of_queries;
  *line >> number_of_arrays >> number_of_queries;

  int sum = number_of_arrays + number_of_queries;
  vector<int> vectors[sum];

  for (int i = 0; i < sum; ++i) {
    line = get_line();
    int n;
    while (*line >> n) vectors[i].push_back(n);
    delete line;
  }

  cout << endl;
  for (int i = number_of_arrays; i < sum; ++i) {
    int vector = vectors[i][0];
    int index = vectors[i][1];
    cout << vectors[vector][index] << endl;
  }
  return 0;
}

以下是我尝试使用引用的一些尝试：

尝试1：

istringstream& get_line() {
  string line;
  getline(cin, line);
  return new istringstream(line);
}
...
istringstream& line = get_line();

错误：

x.cpp: In function ‘std::istringstream& get_line()’:
x.cpp:10:32: error: invalid initialization of non-const reference of type ‘std::istringstream& {aka std::__cxx11::basic_istringstream<char>&}’ from an rvalue of type ‘std::istringstream* {aka std::__cxx11::basic_istringstream<char>*}’
   return new istringstream(line);
                            ^
x.cpp: In function ‘int main()’:
x.cpp:23:12: error: type ‘std::istringstream {aka class std::__cxx11::basic_istringstream<char>}’ argument given to ‘delete’, expected pointer
     delete line;

尝试2：

const istringstream& get_line() {
  string line;
  getline(cin, line);
  const istringstream* is = new istringstream(line);
  return is;
}
...
istringstream& line = get_line();

错误：

x.cpp: In function ‘const istringstream& get_line()’:
x.cpp:11:10: error: invalid initialization of reference of type ‘const istringstream& {aka const std::__cxx11::basic_istringstream<char>&}’ from expression of type ‘const istringstream* {aka const std::__cxx11::basic_istringstream<char>*}’
   return is;
          ^
x.cpp: In function ‘int main()’:
x.cpp:21:35: error: binding ‘const istringstream {aka const std::__cxx11::basic_istringstream<char>}’ to reference of type ‘std::istringstream& {aka std::__cxx11::basic_istringstream<char>&}’ discards qualifiers
     istringstream& line = get_line();
                                   ^
x.cpp:24:12: error: type ‘std::istringstream {aka class std::__cxx11::basic_istringstream<char>}’ argument given to ‘delete’, expected pointer
     delete line;
            ^

代码在做什么：

这是一个编码站点难题的变体：

输入：

2 3 // //在此行之后，我将指定2个数组和3个查询

1 2 3 4 5 //数组0

6 7 8 //数组1

0 3 //查询（返回数组0的索引3处的元素）

1 1 //查询（返回数组1的索引1处的元素）

1 2 //等

输出：

4

7

8

Answer 1

按值返回，例如：

#include <iostream>
#include <sstream>

std::istringstream get_line() {
    std::cout << "enter: ";
    std::string line;
    std::getline(std::cin, line);
    std::istringstream rv(line);
    // set the state of the stringstream to whatever state std::cin is in to
    // be able to detect EOF or error conditions outside this function
    rv.setstate(std::cin.rdstate());
    return rv;
}

int main() {
    std::istringstream ss;

    while(ss = get_line()) { // loop while the state is good
        std::string a;
        while(ss >> a) { // extract
            std::cout << a << "\n";
        }
    }
}

您还可以取消对从new获得的指针进行引用，以从函数中返回引用-但由于delete对{ {1}}对于使用该功能的任何人都不是显而易见的。在这种情况下，需要stringstream。 不要这样做：

delete &line;

有没有办法重写一个函数，该函数返回指向istringstream的指针以代替返回引用？

1 个答案: