strstr() / strchr() / strrchr()

Since:		C89（1989）

Functions that search for a specific substring or character within a string. Commonly used in parsers, log analysis, and other tasks where you need to extract information from a string.

Syntax

// Searches for needle within haystack.
// Returns: a pointer to the first occurrence, or NULL if not found.
char *strstr(const char *haystack, const char *needle);

// Searches for character c in string s from the beginning.
// Returns: a pointer to the first occurrence, or NULL if not found.
char *strchr(const char *s, int c);

// Searches for character c in string s from the end (finds the last occurrence).
char *strrchr(const char *s, int c);

// Returns a pointer to the first character in s that matches any character in accept.
char *strpbrk(const char *s, const char *accept);

Function List

Function	Search target	Direction	Description
strstr()	Substring	Forward	Returns a pointer to needle if it exists within haystack.
strchr()	Single character	Forward	Returns the position of the first occurrence of the character. Can also search for the null character ('\0').
strrchr()	Single character	Backward	Returns the position of the last occurrence of the character. Often used to extract a file extension from a path.
strpbrk()	Character set	Forward	Returns the position of the first character in s that matches any character in accept.

Sample Code

sample_strstr_strchr_strrchr.c

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

int main(void) {
    const char *path = "/home/user/documents/report.txt";

    // Use strstr to check whether the path contains "documents".
    if (strstr(path, "documents")) {
        printf("The file is inside the documents folder.\n");
    }

    // Use strchr to find the position of the first '/'.
    char *first_slash = strchr(path, '/');
    printf("From the first '/': %s\n", first_slash); // "/home/user/documents/report.txt"

    // Use strrchr to extract the file extension from the path.
    char *ext = strrchr(path, '.');
    if (ext) {
        printf("Extension: %s\n", ext); // ".txt"
    }

    // Use strrchr to extract the filename from the path.
    char *filename = strrchr(path, '/');
    if (filename) {
        printf("Filename: %s\n", filename + 1); // "report.txt"
    }

    // Use strpbrk to find the position of a delimiter (comma or semicolon).
    const char *csv = "Yagami Iori,Terry Bogard;Blue Mary";
    char *sep = strpbrk(csv, ",;");
    if (sep) {
        printf("First delimiter: '%c'\n", *sep); // ','
    }

    return 0;
}

gcc strstr_strchr_strrchr.c -o strstr_strchr_strrchr
./strstr_strchr_strrchr
The file is inside the documents folder.
From the first '/': /home/user/documents/report.txt
Extension: .txt
Filename: report.txt
First delimiter: ','

Notes

These functions return a pointer to the found position, which lets you continue processing from the middle of the original string. Always check whether the return value is NULL before using it. Dereferencing a NULL pointer causes undefined behavior.

You can calculate a zero-based index by subtracting the start address of the string from the found position (e.g., pos - haystack).

For string copying and concatenation, see strlen() / strcpy() and strcat().

If you find any errors or copyright issues, please contact us.

Home