如何将数组内容写入硬盘

Question

i am trying to write content of a very large char array to the hard disk. I have the following array(actually the size of it is going to be very large) I am using the array as a bit array and after inserting a specified number of bits into it I have to copy its content to another array and write this copy into hard disk. I then empty the content of the array by assigning it 0 for further use.

unsigned char       bit_table_[ROWS][COLUMNS];

Answer 1

Use ofstream , copy and ostream_iterator to leverage the power of STL:

#include <algorithm>
#include <fstream>
#include <iterator>
#include <iostream>
#include <vector>

using namespace std;

int main() {
    unsigned char bit_table_[20][40];
    for (int i = 0 ; i != 20 ; i++)
        for (int j = 0 ; j != 40 ; j++)
            bit_table_[i][j] = i^j;
    ofstream f("c:/temp/bit_table.bin", ios::binary | ios::out);
    unsigned char *buf = &bit_table_[0][0];
    copy(buf, buf+sizeof(bit_table_), ostream_iterator<unsigned char>(f, ""));
    return 0;
}

Answer 2

You should open a file for writing, and then write the array to it:

FILE * f;
f = fopen(filepath, "wb"); // wb -write binary
if (f != NULL) 
{
    fwrite(my_arr, sizeof(my_arr), 1, f);
    fclose(f);
}
else
{
    //failed to create the file
}

References: fopen , fwrite , fclose

Answer 3

Use a file or a database...

a file is simple to create :

FILE * f;
int i,j;
f = fopen("bit_Table_File", "w");
for (i = 0 , i< ROWS , i++)
{
    for (j = 0 , j < COLUMNS , j++)
    {
        fprintf(f, "%2x", bit_table_[i][j]);
    }
}

to read the contents of the file, you can use fscanf starting from the beginning of the file :

FILE* f = fopen("myFile","r");
for (i = 0 , i< ROWS , i++)
    {
        for (j = 0 , j < COLUMNS , j++)
        {
            fscanf(f, "%2x", &(bit_table_[i][j]));
        }
    }

whereas you have to install a database (and number of tables needed) and use specific instructions to write to it.

Answer 4

You can Store the value of array in file

so you need

• include the fstream header file and using std::ostream;

• declare a variable of type ofstream

• open the file

• check for an open file error

• use the file

• close the file when access is no longer needed

   #include <fstream> using std::ofstream; #include <cstdlib> int main() { ofstream outdata; int i; // loop index int array[5] = {4, 3, 6, 7, 12}; outdata.open("example.dat"); // opens the file if( !outdata ) { // file couldn't be opened cerr << "Error: file could not be opened" << endl; exit(1); } for (i=0; i<5; ++i) outdata << array[i] << endl; outdata.close(); return 0; }