for Robot Artificial Inteligence

22. Fstream(2)

22 Sep 2019 | C++

Comparing content of two files

read 함수

basic_istream& read(char_type* s, std::streamsize count);
  • istream::read(istream에서 정의 됨)
  • 스트림에서 문자들을 받아온다.
  • 이 함수는 sentry (警卫)객체를 먼저 생성한 후, 이를 확인한 다음에 s 가 가리키는 공간에 문자들을 읽어와서 저장합니다. 이 떄 아래 조건을 만족할 때 까지 문자들을 계속 읽어들이게 됩니다.
    • count 개의 문자들을 읽었을 때
    • EOF 가 발생하였을 때 (이 경우 setstate(failbit eofbit) 이 호출되었을 것입니다.) 읽어들인 문자의 수는 gcount() 함수를 호출함으로써 알아낼 수 있습니다.
  • 인자들
    • s - 읽어들인 문자들을 저장할 문자 배열
    • count - 문자 몇 개를 읽을 것인지.
  • 리턴값
    • (asterisk)this

Example 1

#include <iostream>
#include <fstream>
#include "string.h"
//ios::ate - At The End - sets pointer at the end of file - the place of pointer can be changed in that mode, it's possible to read and write in that mode
using namespace std;

bool areFilesEqual(fstream *, fstream *); // fstream doesn't have copy constructor, so we use pointer
int sizeOfFile(fstream *);
int main()
{
    /*
        read(where to read, how many bytes to read);
        memcmp it stands memory compare
    */

    fstream file1, file2;

    file1.open("sample.txt", ios::in | ios::binary | ios::ate);
    file2.open("sample2.txt", ios::in | ios::binary | ios::ate);

    if (file1.is_open() && file2.is_open())
    {
        if (areFilesEqual(&file1, &file2))
        {
            cout << "Files are equal";
        }
        else
            cout << "Files are not the same" << endl;

    }
    else
        cout << "The file couldn't be opened properly" << endl;

    return 0;
}
bool areFilesEqual(fstream *a, fstream *b)
{
    int fileSize1 = sizeOfFile(a);
    int fileSize2 = sizeOfFile(b);

    if (fileSize1 == fileSize2)
    {
        int BUFFER_SIZE;

        if(fileSize1 > 1024)
            BUFFER_SIZE = 1024;
        else
            BUFFER_SIZE = fileSize1;

        char *file1buffer = new char[BUFFER_SIZE]; //쓸데없는 휘발성 값이니
        char *file2buffer = new char[BUFFER_SIZE];

        do
        {
            a->read(file1buffer, BUFFER_SIZE);
            b->read(file2buffer, BUFFER_SIZE);

            if (memcmp(file1buffer, file2buffer, BUFFER_SIZE) != 0)
            {
                cout << "Files are not equal, at least one of the byte was different" << endl;

                delete [] file1buffer;
                delete [] file2buffer;
                return false;
            }
        }while(a->good() && b->good()); //a->good() means a is good() state, and b->good means iit is good() state

        delete [] file1buffer;
        delete [] file2buffer;
        return true;
    }
    else
    {
        cout << "Size of Files are not equal" << endl;
        return false;
    }
}
int sizeOfFile(fstream * file)
{
    file->seekg(0, ios::end); //check the from begging to end
    int sizeOfFile = file->tellg(); // check the pointor position
    file->seekg(0, ios::beg); // and back the pointer of position as origin
    return sizeOfFile;
}

Extracting Characters from files

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    /*
        getline(where to store the extracted characters, how many characters should be taken unless, separator(delimiter)) - extracts seperators and delete it
        get(where to store the extracted characters, how many characters should be taken unless, separator(delimiter)) - doesn't extract seperator
        ignore(how_many_characters_to_extracte AND TO IGNORE THEM, separator) - extracts characters

        get();
    */

    fstream file;

    file.open("sample.txt", ios::in | ios::binary);

    if (file.is_open())
    {
        char first, second;
        char buffer[50];

        cin >> buffer;
        // cin >> getline(buffer, 50) it can get all the word how many word i write, but just cin >> buffer if there is 'space' it just stop

        cout << buffer << endl;
        do
        {
            file.getline(buffer, 50, ' '); // ' ' <- this is just delimeter , so if we change it to 'a', this function will be reading by a. (예로 나는 사람이다에서 띄어쓰기 부분 ' ' <- 에서 멈춘다)
            // 50 means we get 50 character from first sentence of last word

            second = file.get(); // 그리고 그 띄어씌기 이후의 문자 하나를 받는다.

            file.ignore(40, '\n'); // '\n' means that in there is seperator

            cout << buffer << " " << second << ". " << endl;

        } while(!file.eof());



    }
    else
        cout << "The file couldn't be opened properly" << endl;

    return 0;
}

result

Gcount Counting Characters from last operation

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    /*
        gcount - Getcharacter Count - get count of extracted characters from last extraction operation
    */

    fstream file;

    file.open("sample.txt", ios::in | ios::binary);

    if (file.is_open())
    {
        char buffer[250];
        do
        {
            file.getline(buffer, 250);

            cout << buffer << " " << file.gcount() << endl;
        }while(!file.eof());
    }
    else
        cout << "The file couldn't be opened properly" << endl;

    return 0;
}

result

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