Strcpy and memcpy programming implementation, strcpymemcpy Programming

Strcpy and memcpy programming implementation, strcpymemcpy Programming

1 char * strcpy (char * dest, char * src) 2 {3 char * d = dest; // back up the input parameters 4 char * s = src; 5 6 int count = 0; 7 8 assert (dest! = NULL & src! = NULL); // pointer validity check
If (src = dest) return src; 11 count = strlen (src) + 1; // calculate the src String Length 12 if (count <= 1) return 0; // src string is empty 13 if (dest <src | dest> = (src + count) 14 {15 while (count --) 16 {* d ++ = * s ++;} // copy 17} 18 else {19 d = dest + count; 20 s = src + count; 21 while (count --) 22 {23 * d -- = * s --; // copy back and forth 24} 25} 26 return dest; 27}

 1 void memcpy(void *pDst,const void *pSrc,size_t size) 2 { 3 　　assert(pDst!=NULL && pSrc!=NULL); 4 　　if((pSrc<pDst)&&((char *)pSrc+size>pDst)) 5 　　{ 6 　　　　char *pstrSrc=(char *)pSrc + size -1; 7 　　　　char *pstrDst=(char *)pDst +size-1; 8 　　　　while(size--) 9 　　　　　　*pstrDst-- = *pstrSrc;10 　　}11 　　else{12 　　　　char *pstrSrc=(char *)pSrc;13 　　　　char *pstrDst=(char *)pDst;14 　　　　while(size--){15 　　　　　　*pstrDst++ = *pstrSrc++;16 　　　}17 }

Strcpy and memcpy have the following three differences.
1. The copied content is different. Strcpy can only copy strings, while memcpy can copy any content, such as character arrays, integers, struct, and classes.
2. The replication method is different. Strcpy does not need to specify the length. It ends with the string Terminator "\ 0" of the copied character, so it is prone to overflow. Memcpy decides the copy Length Based on its 3rd parameters.
3. Different purposes. Strcpy is usually used to copy strings, while memcpy is generally used to copy data of other types.

C ++ strcpy function implementation

/*
1123rty
1123rty
1123rty
Press any key to continue
*/
# Include <stdio. h>
Char * strcopy (char * strDest, const char * strSrc ){
Char * tempptr = strDest;
While (* tempptr ++ = * strSrc ++ );
Return strDest;
}

Int main (){
Char aa [100];
Char bb [100];
Gets (bb );
Strcopy (aa, bb );
Puts (aa );
Puts (bb );
Return 0;
}

Programming: Can I use a custom function to implement the functions of string processing functions strcat, strcpy, strcmp, strlen, and strlwr?

I don't know what strlwr is?
1. strcat
Void mycat (char * s1, char * s2)
{
While (* s1 ++ );
S1 --;
While (* s1 ++ = * s2 ++ );
}
2. strcpy
Void mycpy (char * s1, char * s2)
{
While (* s1 ++ = * s2 ++ );
}
3. strcmp
Int mycmp (char * s1, char * s2)
{
For (; * s = * t; s ++, t ++)
If (* s = 0) return 0;
Return * s-* t;
}
4. strlen
Int mylen (char * s1)
{
Char * p = s1;
While (* p ++ );
Return p-s-1;
}