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[英]Read amount of lines from a text file and store them as a constant int for array size c++
[英]C++ programming define array size from the external text file
我試圖使我的數組具有非常量值的大小。 大小應由從中獲取信息的“test.txt”文件定義。 例如,如果 txt 文件有 10 個數字,則數組的大小應為 10。我嘗試使用向量,但無法使其工作。 任何幫助將非常感激。 這是下面的代碼:
#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<vector>
#include<cstdlib>
using namespace std;
/* Function to print an array
A int[]: an array of n element
n int; length of an array
*/
void displayList(float A[], int n)
{
int i;
for (i = 0; i < n; i++)
cout << A[i] << ", ";
cout << endl;
}
/*
Insertion Sort function
A int[]: an array of n element
n int; length of an array
*/
void insertionSort(float A[], int n)
{
int i, j;
float key;
for (i = 1; i < n; i++)
{
key = A[i];// take key
j = i - 1;
/* Move elements of arr[0..i-1], that are
greater than key, to one position ahead
of their current position */
while (j >= 0 && A[j] > key)
{
A[j + 1] = A[j]; // move element to next postion
j = j - 1; // reduce index of j - go backward in the array
}
std::cout << "Step key at i = " << i << ": [" << key << "] inserted at j = " << j + 1 << "
position -> ";
A[j + 1] = key; // at j+1 th position we place the key
displayList(A, n);
}
};
ifstream input("test.txt"); //put your program together with thsi file in the same folder.
int main() {
int const ARRAY_SIZE = 9;
float A[ARRAY_SIZE];
string line;
ifstream inFile;
int i = 0, cnt = 0;
float n;
inFile.open("test.txt");
if (!inFile) {
cout << "Unable to open file";
exit(1); // terminate with error
}
while (!inFile.eof()) {
getline(inFile, line);
n = atof(line.c_str());
cnt++;
}
int cnt;
cin >> cnt;
vector<float> A(cnt);
inFile.close();
inFile.open("test.txt");
if (!inFile) {
cout << "Unable to open file";
exit(1); // terminate with error
}
while (!inFile.eof()) {
getline(inFile, line);
n = atof(line.c_str());
A[cnt++] = n;
}
inFile.close();
n = sizeof(A) / sizeof(A[0]);
cout << "insertionSort: \n";
cout << "Unsorted array: ";
displayList(A, n);
insertionSort(A, n);
std::cout << "Sorted array: ";
displayList(A, n);
}
來自 txt 文件的示例輸入:
12
4
5
9
6
11
0
2
0.5
要使其與vector
一起使用,您不應該創建具有多個元素的vector<float> v(10);
,例如vector<float> v(10);
. 創建一個空vector
並一次添加一個值。
void display(const std::vector<float>& A) {
std::cout << "Got " << A.size() << " elements.\n";
for(float value : A) {
std::cout << value << '\n';
}
}
int main() {
std::vector<float> A; // an empty vector of floats
float temp; // a temporary float to use for extraction
while(input >> temp) { // loop while extraction succeeds
A.push_back(temp); // save the value at the end of the vector
}
display(A);
}
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