C++ String strpbrk() Function

What You’ll Learn

The strpbrk() function scans a C-string and returns a pointer to the first character that belongs to a given set. The name means string span break—where the scan “breaks” because a matching character from the set was found. It is the pointer-based partner of strcspn().

Definition and Usage

In C++, strpbrk() is declared in <cstring>. It walks str1 from the beginning and checks each character against every character stored in str2. The first hit stops the search and returns a pointer into str1 at that position.

Treat str2 as a bag of characters, not a phrase. Passing "aeiou" finds the first vowel. Passing ",;" finds the first comma or semicolon. If nothing matches, you get nullptr.

📝 Syntax

Function signature and a typical call:

#include <cstring>

const char* strpbrk(const char* str1, const char* str2);

// Example:
const char* p = strpbrk("Hello, World!", "aeiou");
// *p == 'e' when p is not nullptr

Parameters

• str1 — the C-string to search (must be null-terminated).
• str2 — a set of characters; any one match in str1 succeeds.

Return Value

Pointer to the first matching character inside str1, or nullptr if no character from str2 appears in str1.

Examples Gallery

Compile with g++ strpbrk.cpp -std=c++17 -o strpbrk. Always check for nullptr before dereferencing the returned pointer.

#include <iostream>
#include <cstring>

int main() {
    const char* text = "Hello, World!";
    const char* vowels = "aeiou";

    const char* result = std::strpbrk(text, vowels);

    if (result != nullptr) {
        std::cout << "First vowel: " << *result << "\n";
        std::cout << "Index:       " << (result - text) << "\n";
    } else {
        std::cout << "No vowel found.\n";
    }

    return 0;
}

First vowel: e
Index:       1

#include <iostream>
#include <cstring>

int main() {
    const char* line = "timeout=30;retries=3";

    const char* delim = std::strpbrk(line, ",;\t");

    if (delim != nullptr) {
        std::cout << "First delimiter: '" << *delim << "'\n";
        std::cout << "Rest of line:    " << delim << "\n";
    }

    return 0;
}

First delimiter: ';'
Rest of line:    ;retries=3

#include <iostream>
#include <cstring>

int main() {
    const char* data = "user@example.com";
    const char* specials = "@.";

    const char* ptr = std::strpbrk(data, specials);
    std::size_t len = std::strcspn(data, specials);

    std::cout << "strcspn length: " << len << "\n";
    if (ptr != nullptr) {
        std::cout << "strpbrk index:  " << (ptr - data) << "\n";
        std::cout << "Matched char:   " << *ptr << "\n";
    }

    return 0;
}

strcspn length: 4
strpbrk index:  4
Matched char:   @

#include <iostream>
#include <cstring>

int main() {
    const char* csv = "C++,Java,Python";
    const char* separators = ",";

    std::size_t fieldLen = std::strcspn(csv, separators);
    const char* comma = std::strpbrk(csv, separators);

    std::cout << "Field 1: ";
    for (std::size_t i = 0; i < fieldLen; ++i) {
        std::cout << csv[i];
    }
    std::cout << "\n";

    if (comma != nullptr) {
        std::cout << "Next field starts at: " << (comma + 1) << "\n";
    }

    return 0;
}

Field 1: C++
Next field starts at: Java,Python

#include <iostream>
#include <cstring>

int main() {
    const char* id = "XR-49281";
    const char* found = std::strpbrk(id, "aeiou");

    if (found == nullptr) {
        std::cout << "No vowels in \"" << id << "\"\n";
    } else {
        std::cout << "Vowel found: " << *found << "\n";
    }

    return 0;
}

No vowels in "XR-49281"

🚀 Common Use Cases

• Finding delimiters — commas, spaces, tabs, or punctuation in config lines.
• Scanning for vowels or symbol classes — first special character in input.
• Tokenization helpers — locate split points in CSV or path strings.
• Validation — detect whether forbidden characters appear in an identifier.
• Pairing with strcspn() — measure prefix, then jump to the delimiter.

📝 Notes

• The returned pointer points into str1—valid only while that memory remains alive.
• str2 is a character set, not a substring to find as a whole.
• Always test for nullptr before dereferencing.
• Case-sensitive: "A" and "a" are different characters.
• C++ alternative: s.find_first_of("aeiou") on std::string.

⚡ Optimization

For small character sets on short strings, strpbrk is fine. For repeated searches with the same large set, building a lookup table (256-byte bitmap for ASCII) can beat naive nested scans. In application code, prefer std::string algorithms unless you are interfacing with C APIs.

💡 Best Practices