calloc

Dynamic memory24

Objective

Implement a function that allocates memory for an array of nmemb elements of size bytes each, sets every byte to zero, and returns the pointer (or NULL on failure).

Steps

Compute the total number of bytes as nmemb * size, then hand that to malloc.
Before multiplying, guard against overflow: when both nmemb and size are non-zero, the product overflows if nmemb > SIZE_MAX / size (SIZE_MAX comes from <stdint.h>). In that case return NULL instead of wrapping around to a tiny allocation, that wrap is a real-world security bug.
After malloc succeeds, write a zero into every one of the allocated bytes. The caller is promised clean memory, so never leave it uninitialized.
Return NULL if malloc fails.
Return the pointer to the zeroed block on success.

examples

$ calloc(4, sizeof(int)) // read back the 4 ints

0 0 0 0

$ calloc(SIZE_MAX, SIZE_MAX) // would overflow, print "null" on NULL

null

Constraints

Expected files

calloc.c

Allowed functions

malloc

Allowed headers

<stdlib.h>declares malloc

<stddef.h>defines size_t

<stdint.h>defines SIZE_MAX

libc

Standard C library

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

Tests

Run the tests to grade your code

Build

01Four ints all initialized to zero

02All eight bytes are NUL

03Multiplication overflow returns NULL

04Overflow that wraps to a tiny size still returns NULL

05Allocated block is usable and NUL-terminated

06Every byte except the marker is zero

07First and last byte of a larger block are zero

08Recycled memory still reads back zeroed

calloc

Objective

Implement a function that allocates memory for an array of nmemb elements of size bytes each, sets every byte to zero, and returns the pointer (or NULL on failure).

Steps

Compute the total number of bytes as nmemb * size, then hand that to malloc.
Before multiplying, guard against overflow: when both nmemb and size are non-zero, the product overflows if nmemb > SIZE_MAX / size (SIZE_MAX comes from <stdint.h>). In that case return NULL instead of wrapping around to a tiny allocation, that wrap is a real-world security bug.
After malloc succeeds, write a zero into every one of the allocated bytes. The caller is promised clean memory, so never leave it uninitialized.
Return NULL if malloc fails.
Return the pointer to the zeroed block on success.

examples

$ calloc(4, sizeof(int)) // read back the 4 ints

0 0 0 0

$ calloc(SIZE_MAX, SIZE_MAX) // would overflow, print "null" on NULL

null

Constraints

Expected files

calloc.c

Allowed functions

malloc

Allowed headers

<stdlib.h>declares malloc

<stddef.h>defines size_t

<stdint.h>defines SIZE_MAX

libc

Standard C library

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

calloc

Dynamic memory24

Objective

Implement a function that allocates memory for an array of nmemb elements of size bytes each, sets every byte to zero, and returns the pointer (or NULL on failure).

Steps

Compute the total number of bytes as nmemb * size, then hand that to malloc.
Before multiplying, guard against overflow: when both nmemb and size are non-zero, the product overflows if nmemb > SIZE_MAX / size (SIZE_MAX comes from <stdint.h>). In that case return NULL instead of wrapping around to a tiny allocation, that wrap is a real-world security bug.
After malloc succeeds, write a zero into every one of the allocated bytes. The caller is promised clean memory, so never leave it uninitialized.
Return NULL if malloc fails.
Return the pointer to the zeroed block on success.

examples

$ calloc(4, sizeof(int)) // read back the 4 ints

0 0 0 0

$ calloc(SIZE_MAX, SIZE_MAX) // would overflow, print "null" on NULL

null

Constraints

Expected files

calloc.c

Allowed functions

malloc

Allowed headers

<stdlib.h>declares malloc

<stddef.h>defines size_t

<stdint.h>defines SIZE_MAX

libc

Standard C library

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

Tests

Run the tests to grade your code

Build

01Four ints all initialized to zero

02All eight bytes are NUL

03Multiplication overflow returns NULL

04Overflow that wraps to a tiny size still returns NULL

05Allocated block is usable and NUL-terminated

06Every byte except the marker is zero

07First and last byte of a larger block are zero

08Recycled memory still reads back zeroed