Problem 0. Suppose a file contains 100 bytes of data. A program successfully opens it for both reading and writing (i.e., passing the mode 0_READWR to open()), and gets back a file descriptor number fd. a. The program, which has a 40-byte buffer, issues a call to read() for 40 bytes. It processes that data, and then repeats the call. Both calls return the exact amount requested. Then it issues a third read, again requesting 40 bytes. What value will it return? (Assume no other program has the file open.) b. Next the program calls write(fd, buffer, 40), and the call returns 40. Then it issues another read() call for 40 bytes. What value does that call return? c. Suppose the programmer needs to read back the 40 bytes just written. First it must use 1seek () to reposition the file pointer. What parameters should it invoke 1seek () with so that the next read call will return the 40 bytes just written?

Problem 0. Suppose a file contains 100 bytes of data. A program successfully opens it for both reading and writing (i.e., passing the mode 0_READWR to open()), and gets back a file descriptor number fd. a. The program, which has a 40-byte buffer, issues a call to read() for 40 bytes. It processes that data, and then repeats the call. Both calls return the exact amount requested. Then it issues a third read, again requesting 40 bytes. What value will it return? (Assume no other program has the file open.) b. Next the program calls write(fd, buffer, 40), and the call returns 40. Then it issues another read() call for 40 bytes. What value does that call return? c. Suppose the programmer needs to read back the 40 bytes just written. First it must use 1seek () to reposition the file pointer. What parameters should it invoke 1seek () with so that the next read call will return the 40 bytes just written?

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

**Problem 0.** Suppose a file contains 100 bytes of data. A program successfully opens it for both reading and writing (i.e., passing the mode `O_READWR` to `open()`), and gets back a file descriptor number `fd`.

a. The program, which has a 40-byte buffer, issues a call to `read()` for 40 bytes. It processes that data, and then repeats the call. Both calls return the exact amount requested. Then it issues a third read, again requesting 40 bytes. What value will it return? (Assume no other program has the file open.)

b. Next, the program calls `write(fd, buffer, 40)`, and the call returns 40. Then it issues another `read()` call for 40 bytes. What value does that call return?

c. Suppose the programmer needs to read back the 40 bytes just written. First it must use `lseek()` to reposition the file pointer. What parameters should it invoke `lseek()` with so that the next read call will return the 40 bytes just written?

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