{"id":269,"date":"2015-11-23T08:09:49","date_gmt":"2015-11-23T08:09:49","guid":{"rendered":"http:\/\/www.csestack.org\/?p=269"},"modified":"2019-03-09T13:49:16","modified_gmt":"2019-03-09T08:19:16","slug":"implement-strstr-function-in-c","status":"publish","type":"post","link":"https:\/\/www.csestack.org\/implement-strstr-function-in-c\/","title":{"rendered":"How to Write a code to implement strstr function in C?"},"content":{"rendered":"

Before implementing strstr function, first\u00a0thing, you need to understand strstr function. What does strstr function\u00a0do? What are its uses?<\/p>\n

What is strstr\u00a0function in C?<\/h4>\n

Strstr is the inbuilt string function given in C language. This function is used to find the substring in other string. Before to write our own code to implement the strstr function in C, I briefly introduce you\u00a0an inbuilt strstr function with its syntax.<\/p>\n

Syntax Declaration for strstr function: <\/strong><\/p>\n

int strstr(char*, char*);<\/code><\/pre>\n
This function is very easy to use in c language. It has two arguments as char strings. First string contents base string in which we want to search sub-string. The Second argument is sub-string that need to be searched in base string.<\/p>\n
If it founds substring in the base string, it returns 1. Otherwise, it returns 0.<\/p>\n
Now here, instead of using an inbuilt strstr function, we want to implement a strstr function in C. This function will work the same like as inbuilt strstr()<\/code> function.<\/p>\n
I have been asked this question in IBM placement interview<\/a> on campus.<\/p>\n
Code to implement strstr function in C<\/h4>\n
Complete C program to write your own strstr\u00a0function.<\/p>\n
[cpp]
\n#include<stdio.h><\/p>\n
int fStrStr(char* str, char* strSub)
\n{
\n\tint i=0, j=0;
\n\tint nTemp = i;
\n\tint nStrLen = strlen(str);
\n\tint nStrSubLen = strlen(strSub);
\n\tfor(i=0; i<nStrLen-nStrSubLen; i++)
\n\t{
\n\t\tnTemp = i;
\n\t\tfor(j=0; j<nStrSubLen; j++)
\n\t\t{<\/p>\n
\t\t\tif(str[nTemp]==strSub[j])
\n\t\t\t{
\n\t\t\t\tif(j==nStrSubLen-1)
\n\t\t\t\t\treturn 1;
\n\t\t\t\tnTemp++;
\n\t\t\t}
\n\t\t\telse
\n\t\t\t\tbreak;
\n\t\t}
\n\t}
\n\treturn 0;
\n}<\/p>\n
int main()
\n{
\n\tchar str[] = "CSEStack";
\n\tchar strSub[] = "SES";<\/p>\n
\tif(fStrStr(str, strSub))
\n\t\tprintf("Sub-string found.");
\n\telse
\n\t\tprintf("Sub-string not found.");<\/p>\n
}<\/p>\n
[\/cpp]<\/p>\n
Output:<\/strong><\/p>\n
Case 1: <\/strong><\/p>\n
char str[] = \"CSEStack\";\r\nchar strSub[] = \"SES\";\r\n=>Sub-string found.<\/pre>\n
Case 2: <\/strong><\/p>\n
char str[] = \"CSEStack\";\r\nchar strSub[] = \"SDS\";\r\n=>Sub-string not found.<\/pre>\n
This is one of the top\u00a0coding questions asked in an interview<\/a>.<\/p>\n
Note:<\/strong> Here, I am using fstrstr()<\/code> function that will work as an inbuilt function strstr()<\/code>. Even you can use the same function name as strstr()<\/code>. If there is inbuilt as well as user-defined function with the same name, the user-defined function will get the\u00a0call.<\/p>\n
Time Complexity:\u00a0<\/strong>O(n^2)<\/code><\/p>\n
As in the worst case, we are comparing every letter in the base string with every letter in the substring, it’s complexity is O(n^2)<\/code>.<\/p>\n
Difficulty Level:<\/strong> Medium<\/p>\n
Do you have any other solution? Let’s code it in the comment section below.<\/p>\n
Happy Programming!<\/p>\n","protected":false},"excerpt":{"rendered":"
Write a program to implement strstr function in C. Complete code explained about implementing string function strstr.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[38,7],"tags":[272],"class_list":["post-269","post","type-post","status-publish","format-standard","hentry","category-c-cpp","category-code","tag-c-string"],"yoast_head":"\nHow to Write a code to implement strstr function in C?<\/title>\n<meta name=\"description\" content=\"Now here instead of using inbuilt strstr function, we want to implement strstr function in C. 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