C String strchr() Function

What You’ll Learn

The strchr() function scans a C-string from left to right and returns a pointer to the first matching character. If the character does not appear, it returns NULL. It is one of the most useful tools for parsing text.

Definition and Usage

strchr stands for string character. It walks the string byte by byte until it either finds the requested character or reaches the null terminator. The returned pointer points into the original string—no new memory is allocated.

Because the result is a pointer into str, you can use it to read the rest of the string starting at that character, or compute how far the match is from the start with pointer subtraction.

📝 Syntax

Standard C declaration:

char *strchr(const char *str, int c);

Parameters

• str — null-terminated string to search.
• c — character to find, passed as int (use 'a' or '\n').

Return Value

• Pointer to the first occurrence of c in str.
• NULL if c is not found (except see note on '\0' below).
• If c is '\0', returns a pointer to the terminating null byte.

Header

• #include <string.h>

Examples Gallery

Compile with gcc strchr.c -std=c11 -o strchr. Every example includes <string.h>.

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

int main(void) {
    const char *sample = "Hello, C Programming!";
    char search = 'C';

    char *result = strchr(sample, search);

    if (result != NULL) {
        printf("Character '%c' found at position: %td\n",
               search, result - sample);
    } else {
        printf("Character '%c' not found.\n", search);
    }

    return 0;
}

Character 'C' found at position: 7

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

int main(void) {
    const char *word = "hello";
    char *p = strchr(word, 'H');

    if (p == NULL) {
        printf("'H' not found (strchr is case-sensitive).\n");
    } else {
        printf("Found at %td\n", p - word);
    }

    return 0;
}

'H' not found (strchr is case-sensitive).

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

int main(void) {
    const char *email = "alex@codetofun.com";
    char *at = strchr(email, '@');

    if (at != NULL) {
        printf("Username: %.*s\n", (int)(at - email), email);
        printf("Domain:   %s\n", at + 1);
    } else {
        printf("Invalid email format.\n");
    }

    return 0;
}

Username: alex
Domain:   codetofun.com

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

int main(void) {
    const char *text = "banana";
    const char *cursor = text;
    char *found;

    printf("Positions of 'a': ");
    while ((found = strchr(cursor, 'a')) != NULL) {
        printf("%td ", found - text);
        cursor = found + 1;
    }
    printf("\n");

    return 0;
}

Positions of 'a': 1 3 5 

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

int main(void) {
    const char *path = "C:\\Users\\Docs\\readme.txt";
    char *slash = strchr(path, '\\');

    while (slash != NULL) {
        printf("Segment starts at: %s\n", slash + 1);
        slash = strchr(slash + 1, '\\');
    }

    return 0;
}

Segment starts at: Users\Docs\readme.txt
Segment starts at: Docs\readme.txt
Segment starts at: readme.txt

🚀 Common Use Cases

• Parse key=value — locate '=' to split configuration lines.
• Validate email — check for a single '@' separator.
• Path handling — find directory separators before extracting filenames.
• CSV rows — find commas between fields.
• Skip whitespace — find the first non-space character in input.

📝 Notes

• Include <string.h>—the old reference example omitted this header.
• Case-sensitive: use tolower on both sides if you need case-insensitive search.
• Searching for '\0' returns a pointer to the string end.
• Do not modify string literals through the returned pointer if str is read-only.
• For raw memory (not C-strings), use memchr() with an explicit length.

⚡ Optimization

Standard library strchr is highly optimized on most platforms. Avoid writing your own scan loop unless you need special behavior. When searching repeatedly in a loop, advance the start pointer past each match instead of rescanning from index 0.

💡 Best Practices