strstr函數的簡單實現

#include <stdio.h>
#include <string.h>

char *my_strstr(char *str,char *substr)
{
	int len1 = strlen(str);
	int len2 = strlen(substr);
	if(!len2)
		return (char *)str;
	while(len1 >= len2)
	{
		len1--;
		if(!memcmp(str,substr,len2))
			return (char *)str;
		str++;
	}
	return NULL;
}

int main(void)
{
	char *str = "Hello world";
	char *substr = "llo";
	printf("%s\n",my_strstr(str,substr));
	printf("%s\n",strstr(str,substr));
	return 0;
}