How do I read a specific selection of bytes from a file type?

Question

I need to read a specific set of bytes from a file type for a project I'm working on.

For example, let's say we have the following open file called "image":

    int fd = open(image, O_RDWR, S_IRWXU);

Let's say I needed to read a specific section of this file starting from an offset from the beginning, say, a section starting at 1024 bytes and ending at 2048 bytes into the file.

I know we have read(),

    int rd = read(fd, &example, sizeof(1024));

and this would read into "example", the first 1024 bytes.

I know fseek exists, which would set a pointer starting where I want to start reading into "example", but only if I have a FILE type, right? I currently only have a name and it's fd,

    char *image;
    int fd;

Can I use file_name or fd in fseek? Or is there a better way to do this?

Answer 1

On Linux, 'pread()' does the trick:

ssize_t pread(int fd, void *buf, size_t count, off_t offset);

It will seek to 'offset', and then read 'count' bytes int 'buf'.

Answer 2

lseek is the equivalent function to fseek, using file descriptors instead of FILE pointers. You can also use pread as Mahonri Moriancumer noted.