String search

Learn advanced search with strstr and strchr.

Substring search with strstr

strstr(haystack, needle) searches for the needle substring inside haystack. On success it returns the address of the first match; on failure it returns NULL.

Example: char *r = strstr("Merhaba dünya", "dün");. Here r holds the start address of the "dünya" part. printf("%s\n", r); prints "dünya". strstr is case-sensitive; "Dün" and "dün" differ. It's good practice to check for NULL before using the result.

Character search with strchr

strchr(s, c) searches for the character c in the string s. On success it returns the address of the first match; on failure it returns NULL.

Example: char *p = strchr("Merhaba", 'a');. Here p holds the address of the first 'a'. While strstr searches substrings, strchr searches a single character. Both return NULL on failure; so the result should be checked before use. Character search is common in parsing and format handling.

Exercise Find and print a substring

Search for the substring with char *r = strstr("Merhaba dünya", "dün");. Print the matched part with printf("%s\n", r);. Include <string.h>.

Show example solution

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

int main(void) {
    char *r = strstr("Merhaba dünya", "dün");
    printf("%s\n", r);
    return 0;
}

Test yourself

Complete the strstr call

char *r = ____("Merhaba dünya", "dün");

Show answer

char *r = strstr("Merhaba dünya", "dün");

Match the search functions

strstr

Searches substring
strchr

Searches character
NULL return

Not found
address return

Found
What does strstr return if not found?
- Empty string
- NULL
- -1
- Index 0
Show answer

NULL — strstr returns NULL on failure; so the result should be checked before use.

Next lesson: String conversion

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