String substring search strstr

Problem:

Function Name: strstr function prototype: char * strstr (const char * str1, const char * str2); Syntax: * strstr (str1, str2) str1: target string expression to search. str2: the string expression to find. return Value: This function returns the address of str2 in str1 for the first time. If no address is found, the return value is null: charstr[]= "1234xyz" ; char *str1= strstr (str, "34" ); Get str1 = "34xyz" 

Method 1:

One pointer scan, when the first letter is the same, the two pointers scan two strings for comparison.

The Code is as follows:

#include <stdio.h>#include <string.h>#include <assert.h>char* mystrstr(const char* str1,const char* str2)//str1 is the original string {    assert(str1 != NULL);    if(str2 != NULL) return (char*)str1;    while(str1 != ‘\0‘){        if(*str1 != *str2) str1++;        else{            char* ori = str1;            char* des = str2;            while(*des != ‘\0‘){                if(*ori == *des){                    ori++;des++;                }                else break;            }            if(*des == ‘\0‘) return str1;        }    }    return NULL;}int main(){    char ori[]="sdggdfhhttyusdfge";    char des[]="ttyu";    char* ret=mystrstr(ori,des);    printf("%s\n", ret);    return 0;}

The result is

[[Email protected] desktop] #./A. Out
Ttyusdfge

 

Method 2:

Similar methods:

#include <stdio.h>#include <string.h>char* mystrstr(const char* str1,const char* str2)//str1 is the original string {    int len2 = strlen(str2);    int len1 = strlen(str1);    if(!len2) return (char*)str1;    while(len1 >= len2){        len1--;        if(!strcmp(str1,str2,len2)) return (char*)str1;        str1++;        }    }    return NULL;}int main(){    char ori[]="sdggdfhhttyusdfge";    char des[]="ttyu";    char* ret=mystrstr(ori,des);    printf("%s\n", ret);    return 0;}

The result is

[[Email protected] desktop] #./A. Out
Ttyusdfge

 

String substring search strstr