C String strpbrk() Function

What You’ll Learn

The strpbrk() function finds the first character in a string that belongs to a set you specify. Think of it as searching for “any of these symbols” in one pass—useful for vowels, whitespace, delimiters, and punctuation.

Definition and Usage

strpbrk stands for string pointer break. It walks s from left to right and stops at the first byte that matches any character listed in accept. The match is a single character, not a substring—accept = "abc" means “find a, b, or c.”

The returned pointer points inside the original string. You can print the character with *result, compute an index with result - s, or continue scanning from result + 1.

📝 Syntax

Standard C declaration:

char *strpbrk(const char *s, const char *accept);

Parameters

• s — null-terminated string to search.
• accept — null-terminated set of characters to find (any one match stops the search).

Return Value

• Pointer to the first matching character in s.
• NULL if no character from accept appears in s.

Header

• #include <string.h>

Examples Gallery

Compile with gcc strpbrk.c -std=c11 -o strpbrk. Every example checks for NULL before using the returned pointer.

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

int main(void) {
    const char s[] = "Hello, C Programming!";
    const char vowels[] = "aeiou";

    char *result = strpbrk(s, vowels);

    if (result != NULL) {
        printf("First vowel found: %c\n", *result);
    } else {
        printf("No vowel found.\n");
    }

    return 0;
}

First vowel found: e

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

int main(void) {
    const char line[] = "name;age:30";

    char *delim = strpbrk(line, ",;:");

    if (delim != NULL) {
        printf("First delimiter '%c' at index %td\n", *delim, delim - line);
    }

    return 0;
}

First delimiter ';' at index 4

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

int main(void) {
    const char digits[] = "12345";
    char *p = strpbrk(digits, "abcdef");

    if (p == NULL) {
        printf("No letters a-f in the string.\n");
    } else {
        printf("Found: %c\n", *p);
    }

    return 0;
}

No letters a-f in the string.

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

int main(void) {
    const char text[] = "one two  three";
    const char *cursor = text;
    const char *spaces = " \t";
    int count = 0;

    while ((cursor = strpbrk(cursor, spaces)) != NULL) {
        count++;
        cursor++;
    }

    printf("Whitespace runs found: %d\n", count);

    return 0;
}

Whitespace runs found: 3

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

int main(void) {
    const char s[] = "token=42";

    char *p = strpbrk(s, "=");
    size_t len = strcspn(s, "=");

    printf("strpbrk char: %c\n", p ? *p : '?');
    printf("strcspn len:  %zu\n", len);

    return 0;
}

strpbrk char: =
strcspn len:  5

🚀 Common Use Cases

• Token parsing — find the first delimiter in key=value or CSV text.
• Input validation — detect forbidden symbols in usernames or paths.
• Text analysis — locate the first vowel, digit, or punctuation mark.
• Lexer-style scans — jump to the next operator character.
• Path handling — find / or \ among separator sets.

📝 Notes

• Case-sensitive byte comparison—not locale-aware.
• accept is a character set, not a substring to find as a whole.
• Return pointer is into s; do not free() it.
• Empty accept makes the function return NULL (no chars to match).
• Pair with strcspn when you need prefix length instead of a pointer.

⚡ Optimization

Library implementations often build a lookup table from accept for faster scans. For tiny sets in hot loops, a hand-written loop can be equally clear. Profile before micro-optimizing—correct NULL checks matter more than shaving comparisons.

💡 Best Practices