strncmp

Writing text without overflowing24

Objective

Implement a function that compares two null-terminated strings, but never looks at more than the first n bytes.

Steps

Scan both strings together, byte by byte, while the index is below n.
Stop as soon as a byte differs, or as soon as you reach a \0 in either string, even if that happens before n.
Compare each byte as an unsigned char, so bytes with the high bit set rank above ordinary ASCII.
Return 0 when the compared bytes all match, a negative value when the first differing byte in s1 is smaller, and a positive value when it is larger.
When n is 0, compare nothing and return 0.
Only the sign of the result is meaningful; do not call any library function.

examples

$ strncmp("ab", "abc", 2)

$ strncmp("ab", "abc", 3)

negative value

Constraints

Expected files

strncmp.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

01Identical strings within n

02Zero length compares nothing

03First differs and is smaller

04First differs and is larger

05Equal prefix, n stops before the difference

06Shorter string runs out first

07n longer than the equal strings

08Stops at NUL, ignores bytes after it

09High byte ranks above low byte

strncmp

Objective

Implement a function that compares two null-terminated strings, but never looks at more than the first n bytes.

Steps

Scan both strings together, byte by byte, while the index is below n.
Stop as soon as a byte differs, or as soon as you reach a \0 in either string, even if that happens before n.
Compare each byte as an unsigned char, so bytes with the high bit set rank above ordinary ASCII.
Return 0 when the compared bytes all match, a negative value when the first differing byte in s1 is smaller, and a positive value when it is larger.
When n is 0, compare nothing and return 0.
Only the sign of the result is meaningful; do not call any library function.

examples

$ strncmp("ab", "abc", 2)

$ strncmp("ab", "abc", 3)

negative value

Constraints

Expected files

strncmp.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.

strncmp

Writing text without overflowing24

Objective

Implement a function that compares two null-terminated strings, but never looks at more than the first n bytes.

Steps

Scan both strings together, byte by byte, while the index is below n.
Stop as soon as a byte differs, or as soon as you reach a \0 in either string, even if that happens before n.
Compare each byte as an unsigned char, so bytes with the high bit set rank above ordinary ASCII.
Return 0 when the compared bytes all match, a negative value when the first differing byte in s1 is smaller, and a positive value when it is larger.
When n is 0, compare nothing and return 0.
Only the sign of the result is meaningful; do not call any library function.

examples

$ strncmp("ab", "abc", 2)

$ strncmp("ab", "abc", 3)

negative value

Constraints

Expected files

strncmp.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

01Identical strings within n

02Zero length compares nothing

03First differs and is smaller

04First differs and is larger

05Equal prefix, n stops before the difference

06Shorter string runs out first

07n longer than the equal strings

08Stops at NUL, ignores bytes after it

09High byte ranks above low byte