File reading in C++

Question

I am working on the image processing through c++, I has to read the header of jpeg image in char format, I has to check the camera/system/device information of image, how can i do it.

Is you problem really about reading a file, or is it about how to find the meta data for the camera? For meta data, you probably need to ask a much more specific question. — Soren, Oct 23 '11 at 21:09
BTW, standard English sentences end with a period, '.', not a comma, ','. — Thomas Matthews, Oct 23 '11 at 22:55

score 1 · Answer 1 · answered Oct 23 '11 at 20:48

If the file isn't too big, you can read it all into memory:

#include <vector>
#include <fstream>

std::ifstream infile("thefile.bin", std::ios::binary);
infile.seekg(0, std::ios::end);

const std::size_t filesize = infile.tellg();
std::vector<char> buf(filesize);

infile.seekg(0, std::ios::beg);
infile.read(buf.data(), filesize);  // or &buf[0] on old compilers

Your file will be stored in the vector buf. If you only want to read the header, you can read smaller chunks, rather than all of filesize, and process them appropriately.

score 0 · Answer 2 · answered Oct 23 '11 at 22:58

In general, the "meta" section of images are a fixed size.

Read the file, using istream::read and binary mode into a vector. Using the image format specification, locate the field you need.

Build multibyte integers one byte a time, rather than trying to cast a location as an integer and reading. This will help you overcome the issue of Endianness.

File reading in C++

2 Answers2