C++ Academy · Lesson

String Algorithms

Search and split efficiently.

String Algorithms is a free C++ Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C++ Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Searching with find

find returns the index of a substring or npos if absent, working directly on a view without copying.

#include <iostream>
#include <string_view>
int main() {
    std::string_view sv = "key=value";
    auto pos = sv.find('=');
    std::cout << pos << "\n"; // 3
}

Checking npos

Always compare a search result against std::string_view::npos before using it as an index.

#include <iostream>
#include <string_view>
int main() {
    std::string_view sv = "abc";
    if (sv.find('z') == std::string_view::npos)
        std::cout << "not found\n";
}

Prefix and Suffix Checks

starts_with and ends_with (C++20) make intent obvious and avoid manual substring comparisons.

#include <iostream>
#include <string_view>
int main() {
    std::string_view sv = "report.pdf";
    std::cout << sv.starts_with("report") << "\n";
    std::cout << sv.ends_with(".pdf") << "\n";
}

Extracting a Field

Combine find with substr to split a key/value pair without allocating new strings.

#include <iostream>
#include <string_view>
int main() {
    std::string_view sv = "name=Ada";
    auto eq = sv.find('=');
    std::cout << sv.substr(0, eq) << " : " << sv.substr(eq + 1) << "\n";
}

Splitting by a Delimiter

You can walk through tokens by repeatedly finding the delimiter and taking subviews, each token is just a view.

#include <iostream>
#include <string_view>
int main() {
    std::string_view sv = "a,b,c";
    size_t start = 0, pos;
    while ((pos = sv.find(',', start)) != std::string_view::npos) {
        std::cout << sv.substr(start, pos - start) << "\n";
        start = pos + 1;
    }
    std::cout << sv.substr(start) << "\n";
}

Finding from the End

rfind searches backward, handy for getting a file extension or the last separator.

#include <iostream>
#include <string_view>
int main() {
    std::string_view path = "/usr/local/bin";
    auto slash = path.rfind('/');
    std::cout << path.substr(slash + 1) << "\n"; // bin
}

Trimming Whitespace

Use find_first_not_of and find_last_not_of with remove_prefix/remove_suffix to trim, all without copying.

#include <iostream>
#include <string_view>
int main() {
    std::string_view sv = "  hi  ";
    sv.remove_prefix(sv.find_first_not_of(" "));
    sv.remove_suffix(sv.size() - 1 - sv.find_last_not_of(" "));
    std::cout << "[" << sv << "]\n"; // [hi]
}

Comparing Views

Views support == and compare for lexicographic comparison, comparing characters, not pointers.

#include <iostream>
#include <string_view>
int main() {
    std::string_view a = "apple", b = "apple";
    std::cout << (a == b) << "\n"; // 1
}

Counting Occurrences

A loop with find advancing past each hit counts how many times a character or substring appears.

#include <iostream>
#include <string_view>
int main() {
    std::string_view sv = "mississippi";
    int count = 0;
    for (size_t p = sv.find('s'); p != std::string_view::npos; p = sv.find('s', p + 1)) ++count;
    std::cout << count << "\n"; // 4
}

Algorithms Stay Allocation-Free

All of these operations work on the same underlying buffer. Tokens and trimmed results are subviews, no heap allocation occurs until you build a std::string.

Mind the Lifetimes

Subviews produced by these algorithms share the original buffer's lifetime. Do not let them outlive the source string.

Quick Check

Check your understanding of string_view algorithms.

Recap

You learned string algorithms on views:

find/rfind return positions or npos.
starts_with/ends_with check prefixes and suffixes.
Split, trim, and tokenize produce allocation-free subviews.
Subviews share the source's lifetime, mind dangling.

Frequently asked questions

Is the “String Algorithms” lesson free?

Yes — the full text of “String Algorithms” is free to read here on the web, and the C++ Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C++ Academy course, upgrade to CoddyKit PRO.

What will I learn in “String Algorithms”?

Search and split efficiently. You practise C++ Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C++ Academy?

No prior experience is required. C++ Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “String Algorithms” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C++ Academy lesson?

Yes. Every C++ Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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