Consider the following code: int main (int argc, char* argv[]) {char buf[] = \"a

Question

Consider the following code: int main (int argc, char* argv[]) {char buf[] = "ab"; in r = open ("file.txt" O_ RDONLY); int r1, r2, pid; r1 = dup (r); read(r, buf, 1); if ((pid = fork()) = = theta) {r1 = open ("file.txt O_RDONLY);} else {waitpid (pid, NULL theta); read (r1, buf, 1); print f ("%s", buf); return theta; Assume that the disk file "file.txt" contains the string of bytes 15213 Also assume that all system calls succeed. What will be the output when this code is compiled and run and why? Explain your answer by providing a high level description of the code functionality.

Explanation / Answer

int main()
{

char buf[] = "ab";   //Defines a character array of size 2.
int r = open("file.txt", O_RDONLY);   //Opens the file file.txt for read only with file descriptor r.
int r1, r2, pid;   //Declares three integers.
r1 = dup(r); //Duplicates a file descriptor r with r1.
read(r, buf, 1);   //Reads 1 byte to buf, from file descriptor r. So, '1' will be read. And now the buf content is: "1b"
if((pid = fork()) == 0)   //If the child is executing.
r1 = open("file.txt", O_RDONLY);   //Opens the file file.txt for read only with file descriptor r1.
else               //If the parent is executing.
waitpid(pid, NULL, 0);   //Wait for child process to complete.
read(r1, buf, 1);   //Initially, the child process reads 1 byte from r1 to buf. So, now w.r.t. child buf content is: "1b"
                        //Later, the parent process reads 1 byte from r1 to buf. So, now w.r.t parent buf content is: "5b"
printf("%s ", buf); //Prints 1b by the child. Then prints 5b by the parent.                     
return 0;
}
//So, the output is: 1b5b

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