有没有办法重写一个返回指向 istringstream 的指针的函数，而不是返回一个引用?

Is there a way to rewrite a function that returns a pointer to an istringstream to instead return a reference?

本文关键字：一个 返回 引用 函数 重写 有没有 istringstream 指针      更新时间：2023-10-16

这是我的代码：

#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：

这是编码网站拼图的变体：

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(数组 0 的索引 3 处返回元素)

11//查询(数组 1 的索引 1 处返回元素)

1 2//等

输出：

四

7

8

按值返回，示例：

#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";
}
}
}

你也可以取消引用从new获得的指针，以返回函数的引用 - 但这完全令人困惑，因为deletestringstream的责任对于使用该函数的人来说并不明显。在这种情况下，人们需要delete &line;。别这样：

#include <iostream>
#include <sstream>
std::istringstream& get_line() {
std::cout << "enter: ";
std::string line;
std::getline(std::cin, line);
std::istringstream* rv = new std::istringstream(line);
// set the state of the stringstream to whatever state std::cin is in
rv->setstate(std::cin.rdstate());
return *rv; // dereference
}
int main() {
std::istringstream& line = get_line();
std::string a;
while(line>> a) { // extract
std::cout << a << "n";
}
delete &line;
}
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