C ++: the fundamental difference between memset, memcpy and strcpy!

# Include <stdio. h>

# Include <stdlib. h>

# Include <string. h>

# Include <assert. h>

 

// Memcpy: copy by byte

Prototype: extern void * memcpy (void * dest, void * src, unsigned int count)

// Function: copy count bytes from the memory area indicated by src to the memory area indicated by dest;

// Same as strcpy

Void * memcpy_su (void * dest, void * src, unsigned int count)

{

Assert (dest! = NULL) & (src! = NULL ));

Char * bdest = (char *) dest;

Char * bsrc = (char *) src;

While (count --> 0)

* Bdest ++ = * bsrc ++;

Return dest;

}

 

 

 

// Strcpy: copy the string. It ends when '\ 0' is encountered.

// Prototype: extern char * strcpy (char * dest, char * src)

// Function: copy the src string ending with '\ 0' to the array indicated by dest;

// Note: the memory areas specified by src and dest cannot overlap and the dest must have enough space to hold strings. Returns the dest pointer.

Char * strcpy_su (char * dest, char * src)

{

Assert (dest! = NULL) & (src! = NULL ));

Char * address = dest;

While (* dest ++ = * src ++ )! = '\ 0 ')

Continue;

Return dest;

}

 

 

// Memset: set the first count byte of the memory area referred to by the buffer, which is replaced by the character c.

// Prototype: extern void * memset (void * buffer, int c, int count );

Void * memset_su (void * buffer, int c, int count)

{

Assert (buffer! = NULL ));

Char * buffer2 = (char *) buffer;

While (count --> 0)

* Buffer2 ++ = c;

Return buffer;

}

 

 

 

 

Void main ()

{

Char str1 [100] = "abchjhgjghjgjgh ";

Char str2 [50] = "efghdfkdjf ";

Strcpy (str1, str2 );

Printf ("% s \ n", str1 );

 

 

Char a [3];

Memset (a, 'A', sizeof (a)-1 );

Memset (& a [2], '\ 0', 1 );

Printf ("% s \ n", );

 

Memcpy (str1, str2, strlen (str2 ));

Printf ("% s \ n", str1 );

 

}