v0.40: Create exercises. Challenge the community.

strstr

Your mission

Implement gm_strstr, your own strstr, which searches a string for the first occurrence of a substring and returns a pointer to where it begins.

See it in action

gm_strstr("git rebase main", "rebase")

Expected result

rebase main

Your checklist

For your own tracking. Tests grade your code.

For each position in haystack, try to match needle character by character starting there.
On the first position where the whole needle matches, return a pointer to that position inside haystack.
If needle never appears, return NULL.
An empty needle matches at the very start: return haystack unchanged.
Watch the restart: when a partial match fails, resume the search from the next character, not from where the partial match stopped, gm_strstr("aaab", "aab") must still find "aab".
Do not modify either input buffer.

More examples

gm_strstr("merge conflict", "xyz")

Expected result

(null)

gm_strstr("commit", "")

Expected result

commit

gm_strstr("aaab", "aab")

Expected result

aab

Constraints

Expected files

strstr.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

libc

Standard C library

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

strstr

Strings: walking and searching

Your mission

Implement gm_strstr, your own strstr, which searches a string for the first occurrence of a substring and returns a pointer to where it begins.

See it in action

gm_strstr("git rebase main", "rebase")

Expected result

rebase main

Your checklist

For your own tracking. Tests grade your code.

For each position in haystack, try to match needle character by character starting there.
On the first position where the whole needle matches, return a pointer to that position inside haystack.
If needle never appears, return NULL.
An empty needle matches at the very start: return haystack unchanged.
Watch the restart: when a partial match fails, resume the search from the next character, not from where the partial match stopped, gm_strstr("aaab", "aab") must still find "aab".
Do not modify either input buffer.

More examples

gm_strstr("merge conflict", "xyz")

Expected result

(null)

gm_strstr("commit", "")

Expected result

commit

gm_strstr("aaab", "aab")

Expected result

aab

Constraints

Expected files

strstr.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

libc

Standard C library

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

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01Needle in the middleWaiting

02Needle at the startWaiting

03Needle absentWaiting

04Empty needle returns the whole haystackWaiting

05Needle longer than haystackWaiting

06Restart after a partial matchWaiting

07Overlapping prefix forces a restartWaiting

08Needle equals haystackWaiting

strstr

Your mission

Implement gm_strstr, your own strstr, which searches a string for the first occurrence of a substring and returns a pointer to where it begins.

See it in action

gm_strstr("git rebase main", "rebase")

Expected result

rebase main

Your checklist

For your own tracking. Tests grade your code.

For each position in haystack, try to match needle character by character starting there.
On the first position where the whole needle matches, return a pointer to that position inside haystack.
If needle never appears, return NULL.
An empty needle matches at the very start: return haystack unchanged.
Watch the restart: when a partial match fails, resume the search from the next character, not from where the partial match stopped, gm_strstr("aaab", "aab") must still find "aab".
Do not modify either input buffer.

More examples

gm_strstr("merge conflict", "xyz")

Expected result

(null)

gm_strstr("commit", "")

Expected result

commit

gm_strstr("aaab", "aab")

Expected result

aab

Constraints

Expected files

strstr.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

libc

Standard C library

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

v0.40: Create exercises. Challenge the community.

Meet Studio →

strstr

Strings: walking and searching

Your mission

Implement gm_strstr, your own strstr, which searches a string for the first occurrence of a substring and returns a pointer to where it begins.

See it in action

gm_strstr("git rebase main", "rebase")

Expected result

rebase main

Your checklist

For your own tracking. Tests grade your code.

For each position in haystack, try to match needle character by character starting there.
On the first position where the whole needle matches, return a pointer to that position inside haystack.
If needle never appears, return NULL.
An empty needle matches at the very start: return haystack unchanged.
Watch the restart: when a partial match fails, resume the search from the next character, not from where the partial match stopped, gm_strstr("aaab", "aab") must still find "aab".
Do not modify either input buffer.

More examples

gm_strstr("merge conflict", "xyz")

Expected result

(null)

gm_strstr("commit", "")

Expected result

commit

gm_strstr("aaab", "aab")

Expected result

aab

Constraints

Expected files

strstr.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

libc

Standard C library

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

Tests

Run the tests to grade your code

Build your code, then check each test here. Open a result to inspect its output.

Build

01Needle in the middleWaiting

02Needle at the startWaiting

03Needle absentWaiting

04Empty needle returns the whole haystackWaiting

05Needle longer than haystackWaiting

06Restart after a partial matchWaiting

07Overlapping prefix forces a restartWaiting

08Needle equals haystackWaiting