CODEWITHSUNDEEP
c++filebinarybuffer
nf313743
nf313743

Reputation: 4227

Reading and writing binary file

I'm trying to write code to read a binary file into a buffer, then write the buffer to another file. I have the following code, but the buffer only stores a couple of ASCII characters from the first line in the file and nothing else.

int length;
char * buffer;

ifstream is;
is.open ("C:\\Final.gif", ios::binary );
// get length of file:
is.seekg (0, ios::end);
length = is.tellg();
is.seekg (0, ios::beg);
// allocate memory:
buffer = new char [length];
// read data as a block:
is.read (buffer,length);
is.close();

FILE *pFile;
pFile = fopen ("C:\\myfile.gif", "w");
fwrite (buffer , 1 , sizeof(buffer) , pFile );

Upvotes: 156

Views: 459454

Answers (8)

HeavenHM
HeavenHM

Reputation: 992

Here is implementation of standard C++ 14 using vectors and tuples to Read and Write Text, Binary and Hex files.

Snippet code :

try {
    if (file_type == BINARY_FILE) {

        /*Open the stream in binary mode.*/
        std::ifstream bin_file(file_name, std::ios::binary);

        if (bin_file.good()) {
            /*Read Binary data using streambuffer iterators.*/
            std::vector<uint8_t> v_buf((std::istreambuf_iterator<char>(bin_file)), (std::istreambuf_iterator<char>()));
            vec_buf = v_buf;
            bin_file.close();
        }

        else {
            throw std::exception();
        }

    }

    else if (file_type == ASCII_FILE) {

        /*Open the stream in default mode.*/
        std::ifstream ascii_file(file_name);
        string ascii_data;

        if (ascii_file.good()) {
            /*Read ASCII data using getline*/
            while (getline(ascii_file, ascii_data))
                str_buf += ascii_data + "\n";

            ascii_file.close();
        }
        else {
            throw std::exception();
        }
    }

    else if (file_type == HEX_FILE) {

        /*Open the stream in default mode.*/
        std::ifstream hex_file(file_name);

        if (hex_file.good()) {
            /*Read Hex data using streambuffer iterators.*/
            std::vector<char> h_buf((std::istreambuf_iterator<char>(hex_file)), (std::istreambuf_iterator<char>()));
            string hex_str_buf(h_buf.begin(), h_buf.end());
            hex_buf = hex_str_buf;

            hex_file.close();
        }
        else {
            throw std::exception();
        }
    }

}

Full Source code can be found here

Upvotes: 5

Zeta
Zeta

Reputation: 981

There is a much simpler way. This does not care if it is binary or text file.

Use noskipws.

char buf[SZ];
ifstream f("file");
int i;
for(i=0; f >> noskipws >> buffer[i]; i++);
ofstream f2("writeto");
for(int j=0; j < i; j++) f2 << noskipws << buffer[j];

Or you can just use string instead of the buffer.

string s; char c;
ifstream f("image.jpg");
while(f >> noskipws >> c) s += c;
ofstream f2("copy.jpg");
f2 << s;

normally stream skips white space characters like space or new line, tab and all other control characters. But noskipws makes all the characters transferred. So this will not only copy a text file but also a binary file. And stream uses buffer internally, I assume the speed won't be slow.

Upvotes: -1

Bj&#246;rn Pollex
Bj&#246;rn Pollex

Reputation: 76788

If you want to do this the C++ way, do it like this:

#include <fstream>
#include <iterator>
#include <algorithm>

int main()
{
    std::ifstream input( "C:\\Final.gif", std::ios::binary );
    std::ofstream output( "C:\\myfile.gif", std::ios::binary );

    std::copy( 
        std::istreambuf_iterator<char>(input), 
        std::istreambuf_iterator<char>( ),
        std::ostreambuf_iterator<char>(output));
}

If you need that data in a buffer to modify it or something, do this:

#include <fstream>
#include <iterator>
#include <vector>

int main()
{
    std::ifstream input( "C:\\Final.gif", std::ios::binary );

    // copies all data into buffer
    std::vector<unsigned char> buffer(std::istreambuf_iterator<char>(input), {});

}

Upvotes: 251

iMajetyHK
iMajetyHK

Reputation: 167

It can be done with simple commands in the following snippet.

Copies the whole file of any size. No size constraint!

Just use this. Tested And Working!!

#include<iostream>
#include<fstream>
using namespace std;
int main()
{
  ifstream infile;
  infile.open("source.pdf",ios::binary|ios::in);

  ofstream outfile;
  outfile.open("temppdf.pdf",ios::binary|ios::out);

  int buffer[2];
  while(infile.read((char *)&buffer,sizeof(buffer)))
  {
      outfile.write((char *)&buffer,sizeof(buffer));
  }

  infile.close();
  outfile.close();
  return 0;
}

Having a smaller buffer size would be helpful in copying tiny files. Even "char buffer[2]" would do the job.

Upvotes: 0

Thomas Matthews
Thomas Matthews

Reputation: 57688

Here is a short example, the C++ way using rdbuf. I got this from the web. I can't find my original source on this: 

#include <fstream>
#include <iostream>

int main () 
{
  std::ifstream f1 ("C:\\me.txt",std::fstream::binary);

  std::ofstream f2 ("C:\\me2.doc",std::fstream::trunc|std::fstream::binary);

  f2<<f1.rdbuf();

  return 0;
}

Upvotes: 17

Alexey Sudachen
Alexey Sudachen

Reputation: 384

 sizeof(buffer) == sizeof(char*)

Use length instead.

Also, better to use fopen with "wb"....

Upvotes: 15

retrodrone
retrodrone

Reputation: 5920

You should pass length into fwrite instead of sizeof(buffer).

Upvotes: 6

jcoder
jcoder

Reputation: 30035

sizeof(buffer) is the size of a pointer on your last line NOT the actual size of the buffer. You need to use "length" that you already established instead

Upvotes: 10

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