Reading and writing binary file - c++

Question

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 );

Answer 1

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), {});
}

Answer 2

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;
}

Answer 3

sizeof(buffer) == sizeof(char*)
Use length instead.
Also, better to use fopen with "wb"....

Answer 4

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

Answer 5

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

Answer 6

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

Answer 7

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.

Answer 8

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.