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Calloc

As explained in Modern C, Third Edition

calloc is a C standard-library function that allocates storage for an array of elements and initializes all allocated bytes to zero.

calloc is the array-oriented allocation function in <stdlib.h>: it reserves storage for a specified number of elements and sets every bit of the new storage to 0. section 13.1

Allocate a cleared integer array

size_t n = 44; int* values = calloc(n, sizeof *values); if (values) { /* values has allocated storage with all bits set to 0 */ free(values); } section 13.4 section 13.1

Use calloc with these constraints:

  • Pass a strictly positive element count and element size. section 13.1
  • Prefer it when an all-bits-zero representation is a valid initialization, basically for integer types. section 13.4
  • Initialize floating-point or pointer-containing objects through assignment or a type-specific initialization function instead. section 13.4
#include <stdlib.h>
void* malloc(size_t size);
void free(void* ptr);
void* calloc(size_t nmemb, size_t size);
void* realloc(void* ptr, size_t size);
void* aligned_alloc(size_t alignment, size_t size);

Shows calloc alongside malloc, free, realloc, and aligned_alloc in its standard-library interface. section 13.1

How Modern C, Third Edition covers it

How deep it goes
Defines the interface and bit-clearing behavior, then limits use to positive sizes and representations where zero bits initialize the type validly.
Examples
Uses an integer-array allocation example and contrasts calloc with assignment-based initialization for other object types.
What it assumes
Assumes familiarity with C objects, allocated storage, arrays, and explicit initialization.
What you can do after
Apply it via <stdlib.h> to obtain cleared storage for suitable dynamically allocated arrays and release that storage afterward.
How it connects
Connects dynamic allocation with malloc, free, realloc, aligned_alloc, and explicit object initialization.
Cover of Modern C, Third Edition
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