COMP1521 2022T2 Q6 — Character encoding (UTF-8)

COMP1521 2022T2 Q6 · 10 marks · C
Topic: Character encoding (UTF-8) · Source: https://cgi.cse.unsw.edu.au/~cs1521/26T1/resources/practice_exams.html

Summary: Extract a UTF-8 substring by code-point range

You have been given 22t2final_q6.c ,
which contains a C function 22t2final_q6 ,
that takes three parameters...

char *utf8_string : a UTF-8 encoded string,
unsigned int range_start : the (inclusive) starting index,
unsigned int range_end : the (exclusive) ending index.

... and returns a char * .

#include <string.h>
#include <stdlib.h>

/**

• given a UTF-8 encoded string,
• return a new string that is only
• the characters within the provided range.

*

• Note:
• range_start is INCLUSIVE
• range_end is EXCLUSIVE

*

• eg:
• "hello world", 0, 5
• would return "hello"

*

• "🍓🍇🍈🍍🍐", 2, 5
• would return "🍈🍍🍐"

**/

char _22t2final_q6 ( char utf8_string , unsigned int range_start , unsigned int range_end ) {
char * new_string = strdup ( utf8_string );

return new_string ;
}

Add code to the function 22t2final_q6 so that,
given the above parameters,
it returns a new string comprised of
the UTF-8 code-points that lie in the range
of range_start to range_end
in the provided utf8_string .

Note that the returned string must be a new string;
i.e. you must not modify the provided
utf8_string -- you must instead
use malloc (or otherwise, such as strdup )
to allocate new memory that you can then return.
main will later free that memory
for you.

For example:

make 22t2final_q6
./22t2final_q6 "hello world" 3 8
22t2final_q6("hello world", 3, 8) returned "lo wo"
./22t2final_q6 "🍓🍇🍈🍍🍐🍖🍧🍆🍊🍞" 2 4
22t2final_q6("🍓🍇🍈🍍🍐🍖🍧🍆🍊🍞", 2, 4) returned "🍈🍍"
./22t2final_q6 "⇜⇿↴↛⇳⇙↜↧⇥↖⇸⇋⇈⇘↟↹⇝↩↥⇊⇇⇓⇟⇬⇩" 22 25
22t2final_q6("⇜⇿↴↛⇳⇙↜↧⇥↖⇸⇋⇈⇘↟↹⇝↩↥⇊⇇⇓⇟⇬⇩", 22, 25) returned "⇟⇬⇩"

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

You can assume that the given string is valid UTF-8.

22t2final_q6_main.c includes a main function to help you test your code.

You may not change the provided 22t2final_q6_main.c file.

You may not change 22t2final_q6 's prototype.

i.e. , 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.

No error checking is necessary or required.

🤖 Adapted: write a COMPLETE C program. Read a UTF-8 string from stdin (one trailing newline ignored). argv[1]=range_start (inclusive), argv[2]=range_end (exclusive), both code-point indices (clamped to the string length). Print the sliced substring + a newline.

Reference verified on the sandbox AND cross-checked against an independent code-point oracle.