C++ String strchr() Function

What You’ll Learn

The strchr() function from <cstring> locates the first occurrence of a character in a null-terminated C-string. It returns a pointer to that character—or nullptr if the character is absent—making it essential for parsing emails, paths, and token boundaries in C-style text.

Definition and Usage

In C++, strchr() is declared in <cstring>. It scans a C-string from left to right until it finds the requested character or reaches the null terminator '\0'. The second parameter is typed as int but is normally a character value such as 'C' or '@'.

When a match is found, the return value points into the original string—you do not get a new copy. Subtracting the base pointer (result - str) yields the zero-based index, a common interview and debugging trick.

📝 Syntax

The standard library declaration:

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

Parameters

• str — pointer to a null-terminated C-string to search.
• character — the character to find, passed as int (e.g. 'C', '@', or 67 for ASCII 'C').

Return Value

Pointer to the first matching character in str, or nullptr if not found. Also returns a pointer to the terminating '\0' when searching for '\0'.

Header

#include <cstring>

Examples Gallery

Compile with g++ strchr.cpp -std=c++17 -o strchr. Each example shows how to search, test for success, and compute positions safely.

#include <iostream>
#include <cstring>

int main() {
    const char* sentence = "Hello, C++!";
    char searchChar = 'C';

    const char* result = strchr(sentence, searchChar);

    if (result != nullptr) {
        std::cout << "Character '" << searchChar
                  << "' found at position: "
                  << (result - sentence) << std::endl;
    } else {
        std::cout << "Character not found." << std::endl;
    }

    return 0;
}

Character 'C' found at position: 7

#include <iostream>
#include <cstring>

int main() {
    const char* word = "Hello";

    const char* found = strchr(word, 'z');

    if (found == nullptr) {
        std::cout << "'z' is not in the word." << std::endl;
    } else {
        std::cout << "Found at " << (found - word) << std::endl;
    }

    return 0;
}

'z' is not in the word.

#include <iostream>
#include <cstring>

int main() {
    const char* email = "user@example.com";
    const char* at = strchr(email, '@');

    if (at != nullptr) {
        std::cout << "Valid format hint: @ at index "
                  << (at - email) << std::endl;
    } else {
        std::cout << "Missing @ symbol." << std::endl;
    }

    return 0;
}

Valid format hint: @ at index 4

#include <iostream>
#include <cstring>

int main() {
    const char* path = "/cpp/string/function/strchr";
    const char* slash = strchr(path, '/');

    while (slash != nullptr) {
        std::cout << "Slash at " << (slash - path)
                  << ", rest: " << slash << std::endl;
        slash = strchr(slash + 1, '/');
    }

    return 0;
}

Slash at 0, rest: /cpp/string/function/strchr
Slash at 4, rest: /string/function/strchr
Slash at 11, rest: /function/strchr
Slash at 20, rest: /strchr

#include <iostream>
#include <string>

int main() {
    std::string text = "Hello, C++!";
    std::size_t pos = text.find('C');

    if (pos != std::string::npos) {
        std::cout << "'C' at index: " << pos << std::endl;
        std::cout << "Suffix: " << text.substr(pos) << std::endl;
    }

    return 0;
}

'C' at index: 7
Suffix: C++!

🚀 Common Use Cases

• Delimiter search — locate '@', ':', '/', or '=' before splitting text.
• Path parsing — find slash characters in file paths (often paired with loops).
• Presence checks — verify a required symbol exists in user input.
• Substring start — use the returned pointer as the beginning of a suffix.
• C API interop — work with libraries that pass char* strings.

📝 Notes

• Search is case-sensitive—'A' and 'a' differ.
• Always test for nullptr before dereferencing or subtracting pointers.
• The return pointer points into the original string—it is not a separate allocation.
• Searching for '\0' returns a pointer to the terminator at the end of the string.
• For the last occurrence, use strrchr() instead.

⚡ Optimization

strchr() is highly optimized in standard libraries and is appropriate for typical string lengths. For repeated searches on the same data, consider scanning once in a loop (as in Example 4) rather than restarting from the beginning unnecessarily. For heavy text processing, higher-level tools (std::string, string views, or parsers) may be clearer and safer.

💡 Best Practices