COMP1521 2022T2 Q5 · 10 marks · C 知识点: 文件I/O（FILE） · 次: fseek/ftell/负索引 · 难度: 中等 Topic: File I/O · Source: https://cgi.cse.unsw.edu.au/~cs1521/26T1/resources/practice_exams.html
一句话 / Summary: 打印前n或除末尾|n|字节
You have been given final_q5.c : a C program with an empty implementation of the function print_bytes .
// COMP1521 22T2 ... final exam, question 5
#include <stdio.h>
void print_bytes ( FILE * file , long n ) { // TODO }
Add code to the function print_bytes so that, if n is positive (or zero), it prints the first n bytes from the provided file file .
If n is negative, it should instead print all but the last |n| bytes of the provided file, where |n| is the absolute value of n ; e.g. if n is -5 , then |n| is 5 .
If n extends outside the range of the file ( e.g. n = 50 or n = -50 in a 10 byte file, then your program should behave as if n was 10 in the first case, and as if n was -10 in the second case. i.e. , extending outside the range of the file has no additional effect.
Note that you cannot assume that the provided file is an ASCII text file. In particular, the provided file may contain NUL bytes (i.e. zero bytes). This means that you cannot use string-based functions such as fgets to read from the provided file.
For example:
make 22t2final_q5 echo 'you are doing great, keep it up!' >my_file ./22t2final_q5 my_file 19 you are doing great ^^^ no terminating newline ./22t2final_q5 my_file 7 you are ^^^ no terminating newline ./22t2final_q5 my_file 10000 you are doing great, keep it up! ./22t2final_q5 my_file -14 you are doing great ^^^ no terminating newline
You may find the functions: fgetc(3) , fseek(3) , ftell(3) , putchar(3) , useful.
🤖 Adapted: write a C program with args
<n> <file>. If n ≥ 0 print the first n bytes of file; if n < 0 print all but the last |n| bytes. n outside the file size is clamped to the file size.Fixture files are provided in the run workspace; reference outputs verified on the sandbox.