[英]Segmentation Fault while accepting input
I am trying to accept the input from user where first line will be Integer to indicate number of testcases我正在尝试接受来自用户的输入,其中第一行将是 Integer 以指示测试用例的数量
if number is 3如果数字是 3
Input will be like输入会像
3
Hello world
hey there, I am John
have a nice day
I am using getline
to read the input我正在使用
getline
读取输入
My code我的代码
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
int n;
cin >> n;
vector<string> arr;
for(int i=0; i<n; i++){
string s;
getline(cin, s);
arr[i] = s;
}
}
Error:错误:
3
Segmentation fault(core dumped)
arr
is an empty vector, so arr[i] = s;
arr
是一个空向量,所以arr[i] = s;
is going to access out of bounds.将访问越界。 The
[]
operator does not grow the vector. []
运算符不会增大向量。 It can only be used to access already existing elements.它只能用于访问已经存在的元素。
You can't create an element of a vector using the []
indexing operator;不能使用
[]
索引运算符创建向量的元素; your line arr[i] = s;
你的行
arr[i] = s;
is trying to assign a string to an element that doesn't (yet) exist .正试图将一个字符串分配给一个不(还)存在的元素。
There are several ways around this: first, you could use the push_back
function to add a new element to the end of the vector, in each loop;有几种方法可以解决这个问题:首先,您可以使用
push_back
函数在每个循环中向向量的末尾添加一个新元素; second, you could use the resize
member to pre-allocate a specified number of elements (which you can then use in the arr[i] = s;
line);其次,您可以使用
resize
成员预先分配指定数量的元素(然后您可以在arr[i] = s;
行中使用); third - and perhaps simplest - you can 'pre-allocate' the elements of the vector by specifying the number of elements in the declaration (constructor), like this:第三个——也许是最简单的——你可以通过在声明(构造函数)中指定元素的数量来“预分配”向量的元素,如下所示:
#include <iostream>
#include <vector>
#include <algorithm>
#include <string> // Need this for the "getline()" function definition
using namespace std;
int main()
{
size_t n; // Indexes and operations on std::vector use "size_t" rather than "int"
cin >> n;
cin.ignore(1); // Without this, there will be a leftover newline in the "cin" stream
// std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // More precise, actually!
vector<string> arr(n);
// arr.resize(n); // Alternative to using 'n' in constructor
for (size_t i = 0; i < n; i++) {
string s;
getline(cin, s);
arr[i] = s;
}
for (auto s : arr) cout << s << endl; // Just to confirm the input values
return 0;
}
There are also a few other issues in your code that I have 'fixed' and commented on in the code I posted.您的代码中还有一些其他问题,我已经“修复”并在我发布的代码中进行了评论。 Feel free to ask for further clarification and/or explanation.
随时要求进一步澄清和/或解释。
EDIT: On the use of the cin.ignore(1);
编辑:关于
cin.ignore(1);
line I added, see Why does std::getline() skip input after a formatted extraction?我添加的行,请参阅为什么 std::getline() 在格式化提取后跳过输入? (and the excellent answers given there) for more details.
(以及那里给出的优秀答案)了解更多详情。
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