Unix

Brief introduction about "tcp & tcpm" in basic unix.

This is a homework of unix class which is all about copy a file, not the TCP(Transmission Control Protocol).

tcp:

Base on read(), write(), lseek() and open() methods to copy a file under unix enviroment. This is an example:
tcp file1 file2 (./a.out file1 file2)
tcp file1 dir
tcp file1 dir/file2
If target is a file, then copy the source into target file. If target is a directory file1 would copyed into this dir.

tcpm:

Copy a file via mmap() and memcpy() instead of read() and write() to make the same usage like tcp.

How to achive tcp:

Here are 2 cores in this case:

1. copy file1 to file2
2. if argv[2] is a dir, copy file1 into this dir.

1.copy a file is wirtten in APUE at Part3.9.

And make sure before read/write you have make sure the files are opened.

    while((read_size = read(fd_src_file, n, BUFFSIEZ)) > 0){
        if ((write_size = write(fd_dest_file, n, read_size)) != read_size){
            perror("write dest_file fail");
            exit(1);
        }
    }

2.copy in target directory

Change avg[2] from "/User/.../Desktop" to "/User/.../Desktop/file2".
This method is not the perfect, even a little bit funny. If you have a better idea you can tell me.

    if (S_ISDIR(buf.st_mode)){
        // change the directory if file copy path is not current dir
        sprintf(copy_file_name,"%s%s%s",argv[2],"/",argv[1]);
        printf("change dir to %s
", copy_file_name);
    }

CODE:

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <string.h>

#define BUFFSIEZ 512

int main(int argc, char const *argv[])
{
    int fd_src_file, fd_dest_file;
    int read_size, write_size;
    char n[BUFFSIEZ];
    char copy_file_name[50];
    struct stat buf;
    // check input
    if (argc != 3){
        printf("a.out src_file to dest_file...
");
        exit(1);
    }

    strcpy(copy_file_name, argv[2]);

    if (lstat(argv[2], &buf) < 0)
    {
        perror("lstat error");
    }
    
    if ((fd_src_file = open(argv[1],O_RDWR,0774)) < 0)
    {
        perror("open src_file fail");
        exit(1);
    }
    else
        printf("open file ok.
");

    if (S_ISDIR(buf.st_mode)){
        // change the directory if file copy path is not current dir
        sprintf(copy_file_name,"%s%s%s",argv[2],"/",argv[1]);
        printf("change dir to %s
", copy_file_name);
    }
    if ((fd_dest_file = open(copy_file_name,O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR,0600)) < 0){
                perror("create dest_file fail");
                exit(1);
    }
    while((read_size = read(fd_src_file, n, BUFFSIEZ)) > 0){
        if ((write_size = write(fd_dest_file, n, read_size)) != read_size){
            perror("write dest_file fail");
            exit(1);
        }
    }
    if (read_size < 0) {
        fprintf(stderr, "read error
");
        exit(1);
    }
    printf("read/write ok
");

    return 0;
}

How to achive tcpm:

Search for mmap() and memcpy is the best way to understand how do these method works. Here is a better blog which introduces using mmap() to copy a file.

http://blog.chinaunix.net/uid-20662363-id-1904142.html

At last

Only when I start to write did I understang the patient I have to pay for my blogs. Greet to all those great tech-bloggers!