josephok

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josephok

from collections import defaultdict

# 构造图
# 顶点由'1', '2', '3', ... '40'构成
def build_gragh():
    graph = dict()
    with open('network.txt') as f:
        lines = f.read().splitlines()
        for vh, line in enumerate(lines, start=1):
            g = dict()

josephok

from collections import Counter

def factors(n):
    f = []
    i = 2
    while n > 1:
        while n % i == 0:
            n /= i
            f.append(i)
        i += 1

josephok

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

int main(int argc, char const *argv[])
{
    int fd, i;

josephok

#include <unistd.h>
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <linux/limits.h>

#define OPEN_MAX 1024

int mydup2(int filedes, int filedes2)

josephok

The tee command reads its standard input until end-of-file, writing a copy of the input
to standard output and to the file named in its command-line argument. (We show
an example of the use of this command when we discuss FIFOs in Section 44.7.)
Implement tee using I/O system calls. By default, tee overwrites any existing file with
the given name. Implement the –a command-line option (tee –a file), which causes tee
   to append text to the end of a file if it already exists. (Refer to Appendix B for a
  description of the getopt() function, which can be used to parse command-line
 options.)

josephok

Write a program that opens an existing file for writing with the O_APPEND flag, and
then seeks to the beginning of the file before writing some data. Where does the
data appear in the file? Why?

It appears at the end. Cause you set O_APPEND, every write will append at the end of the file.

josephok

After each of the calls to write() in the following code, explain what the content of
the output file would be, and why:
fd1 = open(file, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
fd2 = dup(fd1);
fd3 = open(file, O_RDWR);
write(fd1, "Hello,", 6);
write(fd2, "world", 6);
lseek(fd2, 0, SEEK_SET);
write(fd1, "HELLO,", 6);
write(fd3, "Gidday", 6);

josephok

Write a program to verify that duplicated file descriptors share a file offset value
    and open file status flags.

josephok

// Write a program to verify that when a child’s parent terminates, a call to getppid()
//  returns 1 (the process ID of init).

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

pid_t fork(void);