read and write a binary file in c++ with fstream

Question

I'm trying to write simple c++ code to read and write a file. The problem is my output file is smaller than the original file, and I'm stuck finding the cause. I have a image with 6.6 kb and my output image is about 6.4 kb

#include <iostream> #include <fstream> using namespace std; ofstream myOutpue; ifstream mySource; int main() { mySource.open("im1.jpg", ios_base::binary); myOutpue.open("im2.jpg", ios_base::out); char buffer; if (mySource.is_open()) { while (!mySource.eof()) { mySource >> buffer; myOutpue << buffer; } } mySource.close(); myOutpue.close(); return 1; }

I was trying to use it to get it's binary characters Like: cout<<static_cast<int>(buffer); — Hadi Rasekh
– Hadi Rasekh, Commented May 5, 2014 at 12:01

Kerrek SB · Accepted Answer · 2014-05-05 11:44:07Z

5

Why not just:

#include <fstream> int main() { std::ifstream mySource("im1.jpg", std::ios::binary); std::ofstream myOutpue("im2.jpg", std::ios::binary); myOutpue << mySource.rdbuf(); }

Or, less chattily:

int main() { std::ofstream("im2.jpg", std::ios::binary) << std::ifstream("im1.jpg", std::ios::binary).rdbuf(); }

answered May 5, 2014 at 11:44

Kerrek SB

480k96 gold badges904 silver badges1.1k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Hadi Rasekh Over a year ago

I was trying to use it to get it's binary characters Like: cout<<static_cast<int>(buffer); This way I can't find its binary data

Kerrek SB Over a year ago

@user3604079: That's why you should ask the question you have, and not something completely unrelated. Please post a new, different question, and make sure that an answer to it is actually helpful to you.

Some programmer dude · Accepted Answer · 2014-05-05 11:42:49Z

Two things: You forget to open the output in binary mode, and you can't use the input/output operator >> and << for binary data, except if you use the output operator to write the input-streams basic_streambuf (which you can get using rdbuf).

For input use read and for output use write.

FSFisGOOD · Accepted Answer · 2014-05-05 16:38:58Z

There are 3 problems in your code:

1- You have not opened your output file in Binary.

2- Your code return "1", normally you should return "0", if something went wrong then return an error code.

3- You should use "manipulators" and make c++ not to avoid whitespaces, so in order to read from file instead of:

mySource >> buffer;

you should use:

mySource >> std:noskipws >> buffer;

RohitArora · Accepted Answer · 2014-05-06 03:55:18Z

Well, its just because of padding at the end of the image. eof of any file do not include the padded bytes added at the end of file. Try this take img1.jpg contains 20 space charecter at the end not visible here (uegfuyregwfyugwrerycgerfcg6ygerbucykgeugcrgfrgeyf ) and run your program (do not include parenthesis in the file, these are used to show the data content) you will see img2.jpg contains (uegfuyregwfyugwrerycgerfcg6ygerbucykgeugcrgfrgeyf)

So, its better option to read the file byte by byte using the filesize which you can get using stat, and run for loop till filesize. Hope this should resolve your problem you mentioned above

Collectives™ on Stack Overflow

read and write a binary file in c++ with fstream

4 Answers 4

2 Comments

Comments

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

Comments

Comments

Related