Implementation of the C-Series function prototype-strstr (char * STR, char * substr)

Ideas:

1. If the last character of the string is '\ 0', it can be used as a critical condition.

2. When * Str! = '\ 0', judge whether * P is equal to * q. If it is equal, move two pointers. If the last * q pointer reaches the boundary, the entire match is successful, return res directly. Otherwise, move the primary string pointer.

# Include <iostream>

Char * mystrstr (char * STR, char * substr ){

While (* Str! = '\ 0 '){

Char * P = STR;

Char * q = substr;

Char * res = NULL;

If (* P = * q ){

Res = P;

While (* Q! = '\ 0' & * P = * q ){

P ++;

Q ++;

}

If (* q = '\ 0 ')

Return res;

}

STR ++;

}

Returnnull;

}

Int main (INT argc, constchar * argv [])

{

Char * S1 = "abcdefghijklmn ";

Char * S2 = "BCD ";

// Search for string 2 in string S1. If the return position is found, otherwise null is returned.

Char * res = mystrstr (S1, S2 );

If (res! = NULL ){

Printf ("% s", Res );

} Else {

Printf ("not ");

}

Printf ("\ n ");

Return0;

}

Result:

Implementation of the C-Series function prototype-strstr (char * STR, char * substr)