<string.h> header functions (1) - memory

Memory Related Function

memcpy : Copy block of memory

void* memcpy(void* destination, const void* source, size_t num);

destination : Pointer to the destination where the content is to be copied, type-casted to a pointer of type *void**.

source : Pointer to the source of data to be copied, type-casted to a pointer of type *const void**.

num : Number of bytes to copy.

#include<stdio.h>
#include<string.h>

struct{
  char name[40];
  int age;
}person, person_copy;

int main() {
  char myname[] = "R.B.Kim";
  memcpy(person.name, myname, strlen(myname)+1);
  person.age = 19;
  
  memcpy(&person_copy, &person, sizeof(person));
  
  printf("person_copy : %s, %d\n", person_copy.name, person_copy.age);
}

person_copy: R.B.Kim, 19

---

memmove : Move block of memory

void* memmove(void* destination, const void* source, size_t num);

same parameters as memcpy

Return Value

• destination is returned

#include<stdio.h>
#include<string.h>

int main()
{
  char str[] = "Now we know memmove";
  memmove(str+12, str+15, 12);
  puts(str);
}

Now we know move

---

memcmp : Compare two blocks of memory

int memcmp(const void* ptr1, const void* ptr2, size_t num);

ptr1 : Pointer to block of memory.

ptr2 : Pointer to block of memory.

num : Number of bytes to compare.

Return Value

• <0 : the first byte that does not match in both memory blocks has a lower value in ptr1 than in ptr2
• =0 : the contents of both memory blocks are equal
• >0 : the first byte that does not match in both meomry blocks has a greater value in ptr1 than in ptr2

#include <stdio.h>
#include <string.h>

int main ()
{
  char buffer1[] = "DWgaOtP12df0";
  char buffer2[] = "DWGAOTP12DF0";

  int n;

  n=memcmp ( buffer1, buffer2, sizeof(buffer1) );

  if (n>0) printf ("'%s' is greater than '%s'.\n",buffer1,buffer2);
  else if (n<0) printf ("'%s' is less than '%s'.\n",buffer1,buffer2);
  else printf ("'%s' is the same as '%s'.\n",buffer1,buffer2);

  return 0;
}

'DWgaOtP12df0' is greater than 'DWGAOTP12DF0'.

---

memchr : Locate character in block of memory

void* memchr (void* ptr, int value, size_t num);

const void* memchr (const void* ptr, int value, size_t num);

ptr : Pointer to the block of memory where the search is performed.

value : Value to be located.

num : Number of bytes to be analyzed.

Return Value

• A pointer to the first occurrence of value in the block of memory pointed by ptr.
• If value is not found, the function returns a NULL pointer.

#include <stdio.h>
#include <string.h>

int main ()
{
  char * pch;
  char str[] = "Example string";
  pch = (char*) memchr (str, 'p', strlen(str));
  if (pch!=NULL)
    printf ("'p' found at position %d.\n", pch-str+1);
  else
    printf ("'p' not found.\n");
  return 0;
}

'p' found at position 5.

---

memset : Fill block of memory

void* memset (void* ptr, int value, size_t num);

ptr : Pointer to the block of memory to fill.

value : Value to be set.

num : Number of bytes to be set to the value.

Return Value

• ptr is returned.

#include <stdio.h>
#include <string.h>

int main ()
{
  char str[] = "almost every programmer should know memset!";
  memset (str,'-',6);
  puts (str);
  return 0;
}

------ every programmer should know memset!