cpipeforklseek

how to copy a file in c byte by byte


okay so I am studying C and in a textbook there is an exercise left for the reader leading up to this exercise the book explains that a file (or at least a regular file) is simply an array of bytes. it is my understanding that in linux each block is 512 bytes but when you read a file into a file descriptor then the program automatically loads up the entire file potentially correct? the book goes over the Linux system calls read, write, and lseek (some basic low-level calls).

now the goal is like i said to copy a file byte by byte to some random new file. pseudo-code will be perfectly acceptable. In any case it is my understanding that you need

My understanding is that the build would go something like this:

#include <all of the req'd headers>

int main(int argc,char** argv) {
    char buff[1]; // byte by byte buffer 
    inf fd = open("filename", O_RDONLY);
    
    int fdp[2]; // for the pipe's fd's
    pipe(fdp);
    
    if( fork() == 0 ) {
        close(fdp[0]);
        
    }

    else {
        write("newfile", buff, 1);
    }

}

for me at least at this stage this is really quite a complex question. My thinking is to read into the file descriptor the entire contents of the file then using a pipe to write byte by byte into a new file copy the entire contents of the previous file into the new file. I am also unsure as to how lseek helps us here in this situation. Or am I over-complicating this and am in the completely wrong direction?


Solution

  • Okay so i have it figured out the solution is actually very simple! Only about 10 lines of code or so here it is:

    #include <unistd.h>
    #include <stdio.h>
    #include <string.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <stdbool.h>
    #include <fcntl.h>
    #include <unistd.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <unistd.h>
    #include <errno.h>
    
    
    
    int main(int argc, char ** argv) { 
        
        char oneByte;
        
        int n;
        int source;
        int destination;
        
        source = open("notes.txt", O_RDONLY);
        destination = open("copiedFile.txt", O_RDWR | O_CREAT, 0644);
        
        while ((n = read(source, &oneByte, 1)) > 0) {
            write(destination, &oneByte, 1);
        }
        
        close(source);
        close(destination);
        
        return 0;
    }