strncat

Writing text without overflowing24

Objective

Write a function that appends at most n characters from src onto the end of dst, then terminates the result.

Steps

Find the end of dst (its current \0) and start writing there.
Copy characters from src until you have appended n of them or reached the end of src, whichever comes first.
Always write a terminating \0 after the appended characters, even when n is 0 or you stopped early.
The gotcha: unlike strncpy, strncat always null-terminates, and n limits how many characters are taken from src, not the total length of the result.
Return dst.

examples

$ strncat("git ", "rebase --interactive", 6)

git rebase

$ strncat("docker ", "compose", 64)

docker compose

$ strncat("commit", " --amend", 0)

commit

Constraints

Expected files

strncat.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

libc

Standard C library

Implements the contract of a function from the standard C library.

Tests

Run the tests to grade your code

Build

01n smaller than src: truncated but terminated

02n larger than src: full append

03n is 0: nothing appended, still terminated

04Append onto an empty dst

05n exactly equals src length

06Empty src leaves dst unchanged

07Truncate src mid-string

strncat

Objective

Write a function that appends at most n characters from src onto the end of dst, then terminates the result.

Steps

Find the end of dst (its current \0) and start writing there.
Copy characters from src until you have appended n of them or reached the end of src, whichever comes first.
Always write a terminating \0 after the appended characters, even when n is 0 or you stopped early.
The gotcha: unlike strncpy, strncat always null-terminates, and n limits how many characters are taken from src, not the total length of the result.
Return dst.

examples

$ strncat("git ", "rebase --interactive", 6)

git rebase

$ strncat("docker ", "compose", 64)

docker compose

$ strncat("commit", " --amend", 0)

commit

Constraints

Expected files

strncat.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

libc

Standard C library

Implements the contract of a function from the standard C library.

strncat

Writing text without overflowing24

Objective

Write a function that appends at most n characters from src onto the end of dst, then terminates the result.

Steps

Find the end of dst (its current \0) and start writing there.
Copy characters from src until you have appended n of them or reached the end of src, whichever comes first.
Always write a terminating \0 after the appended characters, even when n is 0 or you stopped early.
The gotcha: unlike strncpy, strncat always null-terminates, and n limits how many characters are taken from src, not the total length of the result.
Return dst.

examples

$ strncat("git ", "rebase --interactive", 6)

git rebase

$ strncat("docker ", "compose", 64)

docker compose

$ strncat("commit", " --amend", 0)

commit

Constraints

Expected files

strncat.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines size_t

libc

Standard C library

Implements the contract of a function from the standard C library.

Tests

Run the tests to grade your code

Build

01n smaller than src: truncated but terminated

02n larger than src: full append

03n is 0: nothing appended, still terminated

04Append onto an empty dst

05n exactly equals src length

06Empty src leaves dst unchanged

07Truncate src mid-string