如何從char數組中讀取數字（int）值

Question

;）我目前正在研究C ++中的文件和文件流

我的問題是：

我需要在文件中寫入幾個數字，然后從文件中讀取數據-如果可以按4 對數據進行建模（％），則僅該數據。主要問題是從文件中讀取數據並將其放入“緩沖區”之后數組，所有數字值都在char數組中轉換為單個字符->“ 100”拆分為“ 1”，“ 0”，“ 0”和“ 89”，例如拆分為“ 8”和“ 9”再次組合在一起，這樣字符將轉換回數字（以100為單位，而不是'1，'0'，'0'）並將它們放入新數組中？

附言：請盡可能簡單:)我還在學習！

#include <iostream>
#include <fstream>
#include <stdlib.h>

using namespace std;

int main()
{
    int numbers [] = {1, 100, 2, 98, 22, 12, 72, 16, 50, 51};
    int array_size = sizeof(numbers)/sizeof(numbers[0]);

                    //Start of file writing
    ofstream To_file ("C:\\CodeBlocks\\My_projects\\Test_KD_Files\\1stFile.txt");

    cout<< "This numbers will be written in file: " <<endl;
    for (int start = 0; start<array_size; start++)
    {
    To_file<< numbers[start] << " ";
    cout<<numbers[start] << ", ";
    }
    cout<<endl <<endl;

    To_file.close();
                    //End of file writing

                //Start of file reading

    char buffer [50];
    int index = 0;

    ifstream Read_it ("C:\\CodeBlocks\\My_projects\\Test_KD_Files\\1stFile.txt");
    cout<<"Data from file: " <<endl;

        while (Read_it.getline(buffer, 50))
        {
        Read_it.getline(buffer, 50); //all read data will be set in array "buffer"

        cout<< endl <<buffer[index];

            while (index<50) 
            {
                if (buffer[index]%4 ==0) //check - does number can be devided by 4
                {
                    cout<<buffer[index]; //display mostly messed numbers and characters
                }
                index++;
            }

        }

    Read_it.close();

    return 0;
}

Answer 1

getline甚至繼續讀取空格，但在行末字符處停止。 因此，getline不是您要搜索的內容。

訣竅是使用>>運算符，當到達空白或換行符時，該運算符將停止讀取。 然后我們使用atoi（）將字符串轉換為整數：

#include <iostream>
#include <fstream>
#include <stdlib.h>

using namespace std;

int main()
{
    int numbers [] = {1, 100, 2, 98, 22, 12, 72, 16, 50, 51};
    int array_size = sizeof(numbers)/sizeof(numbers[0]);

                    //Start of file writing
    ofstream To_file ("File.txt");

    cout<< "This numbers will be written in file: " <<endl;
    for (int start = 0; start<array_size; start++)
    {
    To_file<< numbers[start] << " ";
    cout<<numbers[start] << ", ";
    }
    cout<<endl <<endl;

    To_file.close();
                    //End of file writing

                //Start of file reading

    int NewNumbers[10];
    char buffer [50];
    int index = 0;

    ifstream Read_it ("File.txt");
    cout<<"Data from file: " <<endl;

    while(Read_it >> buffer)  // we use extraction >> operator to read until white space
    {
        NewNumbers[index] = atoi(buffer);
        index++;
    }

    for(int i(0); i < 10; i++)
        cout << NewNumbers[i] << ", ";

    cout << endl << endl;


    Read_it.close();

    return 0;
}