Analysis and Implementation of the C language function strstr ()

The following is a detailed analysis of the use of the strstr () function in C language. For more information, see

Prototype: char * strstr (const char * str1, const char * str2 );
# Include <string. h>
Locate the position where the str2 string first appears in the str1 string (excluding the str2 string Terminator ). Returns the pointer to this position. If no pointer is found, a null pointer is returned.
Returns a pointer to the first occurrence of strSearch in str, or NULL if strSearch does not appear in str. IfstrSearch points to a string of zero length, the function returns str.

Copy codeThe Code is as follows:
# Include <stdio. h>
# Include <conio. h>
# Include <string. h>
# Include <stdlib. h>
# Pragma warning (disable: 4996)
Char * mystrstr (char * s1, char * s2 );
Int main (void)
{
Char * s = "Golden Global View ";
Char * l = "ob"; // char * l = ""
Char * p;
System ("cls ");
P = mystrstr (s, l );
If (p! = NULL)
{
Printf ("% sn", p );
}
Else
{
Printf ("Not Found! N ");
}
Getch ();
Return 0;
}
/* FROM encyclopedia */
Char * mystrstr (char * s1, char * s2)
{
Int n;
If (* s2) // two considerations
{
While (* s1)
{
For (n = 0; * (s1 + n) = * (s2 + n); n ++)
{
If (! * (S2 + n + 1) // determines whether the next character to be searched is''
{
Return (char *) s1;
}
}
S1 ++;
}
Return NULL;
}
Else
{
Return (char *) s1;
}
}

Another implementation:

Copy codeThe Code is as follows:
Char * strstr (buf, sub)
Register char * buf;
Register char * sub;
{
Register char * bp;
Register char * sp;
If (! * Sub)
Return buf;
While (* buf)
{
Bp = buf;
Sp = sub;
Do {
If (! * Sp)
Return buf;
} While (* bp ++ = * sp ++ );
Buf + = 1;
}
Return 0;
}

Another implementation:

Copy codeThe Code is as follows:

# Include <iostream>
# Include <string>
Using namespace std;
// Implement strstr in C Language
Const char * isSub (const char * str, const char * subs ){
// Special Case
If (! * Subs)
Return str;
Const char * tmp = str;
While (* tmp! = '')
{
// Used to move the parent string one character backward each time
Const char * tmp1 = tmp;
// Record the substring address
Const char * sub1 = subs;
While (* sub1! = ''& * Tmp1! = '')
{
// Jumps out if they are not equal, and removes a character from the parent string
If (* sub1! = * Tmp1)
Break;
// If the child string is equal and the next character is the end of the Child string, it is the child string of the parent string.
If (* sub1 = * tmp1 & * (sub1 + 1) = '')
Return tmp;
// If the values are equal, continue to compare the next character.
If (* sub1 = * tmp1)
{
Sub1 ++;
Tmp1 ++;
}
}
Tmp ++;
}
Return NULL;
}
Int main (){
Char * str1 = "ababcdddb ";
Char * str = "";
Const char * res = isSub (str1, str );
If (res! = NULL)
{
Cout <res <endl;
}
Else
Cout <"null" <endl;
// Cout <isSub (str1, str) <endl;
Return 0;
}