COMP1521 2022T3 Q7 · 字符编码

COMP1521 2022T3 Q7 · 10 marks · C
知识点: 字符编码（UTF8） · 次: 字符串/校验/替换 · 难度: 进阶
Topic: Character encoding (UTF-8) · Source: https://cgi.cse.unsw.edu.au/~cs1521/26T1/resources/practice_exams.html

一句话 / Summary: 把非法UTF-8序列替换为问号

You have been given 22t3final_q7.c ,
which contains a C function _22t3final_q7 ,
that takes a string,
and returns it unmodified.

Add code to the function _22t3final_q7 so that,
given a UTF-8 encoded string,
it returns a new string that has any invalid UTF-8 sequences replaced with the character '?'.

For example:

xxd 22t3final_q7_examples/hello_world.txt
00000000: 6865 6c6c 6f20 776f 726c 64 hello world
./22t3final_q7 < 22t3final_q7_examples/hello_world.txt
hello world
xxd 22t3final_q7_examples/bad_hello_world.txt
00000000: 6865 6c6c 6fa1 776f 726c 64 hello.world
./22t3final_q7 < 22t3final_q7_examples/bad_hello_world.txt
hello?world
xxd 22t3final_q7_examples/valid_with_emoji.txt
00000000: 796f 7520 6172 6520 646f 696e 6720 6772 you are doing gr
00000010: 6561 7420 f09f 918d f09f 918d f09f 918d eat ............
./22t3final_q7 < 22t3final_q7_examples/valid_with_emoji.txt
you are doing great 👍👍👍
xxd 22t3final_q7_examples/invalid_with_emoji.txt
00000000: 7468 6973 f0a1 3923 7374 7269 6e67 a269 this..9#string.i
00000010: 73e7 8936 6e6f 74a0 646f 696e 67c2 c273 s..6not.doing..s
00000020: 6fa0 6772 6561 74f1 3242 a068 6f77 6576 o.great.2B.howev
00000030: 6572 20f0 9f98 ad91 er .....
./22t3final_q7 < 22t3final_q7_examples/invalid_with_emoji.txt
this?string?is?not?doing?so?great?however 😭?

Further example inputs are provided in the 22t3final_q7_examples/ directory.

You can use make(1) to build your code:

make 22t3final_q7

A reminder of how UTF-8 is encoded:

#bytes
#bits
Byte 1
Byte 2
Byte 3
Byte 4

1
7
0xxxxxxx
-
-
-

2
11
110xxxxx
10xxxxxx
-
-

3
16
1110xxxx
10xxxxxx
10xxxxxx
-

4
21
11110xxx
10xxxxxx
10xxxxxx
10xxxxxx

The provided string may be of any length.

The provided string will not contain any null bytes, apart from the terminating null byte.

Each occurrence of a continuation byte outside a sequence should be replaced with a '?'.

If a valid starting byte occurs within another UTF-8 sequence, it should be considered part of
that sequence, thus rendering the sequence invalid. It should not be considered the start of a
new sequence.

22t3final_q7_main.c includes a main function to help you test your code.

You may not change the provided 22t3final_q7_main.c file.

You may not change _22t3final_q7 's prototype.

ie: its return type and its argument types.

You may define and call your own functions if you wish.

Your solution must be in C only.

Your solution must not be in MIPS , C++ , Python , or any other language.

Your program cannot call external programs.

Your program cannot use any of: fork() / exec() , posix_spawn() , system() , or any other similar functions.

Your program may call any functions from the C standard library available by default on CSE Linux systems.

Including but not limited to: stdio.h , stdlib.h , string.h , math.h , assert.h , etc.

🤖 Adapted: write a C program. argv[1] is a filename (delivered as raw bytes). Copy it to stdout, replacing every invalid UTF-8 sequence with a single ? (a bad lead byte consumes 1 byte; a broken/truncated multi-byte sequence consumes its expected length).

Verified on the sandbox, cross-checked against an independent decoder, and reproduces every official example (raw-byte fixtures).