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libstemmer – Snowball Stemming Library

Library: libstemmer (Snowball) Languages: C, C++, bindings in many others

Overview​

libstemmer is a lightweight stemming library implementing the Snowball stemming algorithms. A stemmer reduces words to their root form (e.g., running → run, jumps → jump), which is essential in many information retrieval (IR) and NLP pipelines to normalize terms before indexing or querying.

Snowball (the algorithm family) was designed by Martin Porter and provides a set of fast, rule‑based stemmers for many languages. The libstemmer project provides C/C++ bindings that can be integrated into retrieval systems, search engines, and text processing pipelines.

Key Features​

  • Rule‑based stemming: Language‑specific suffix stripping.
  • Multi‑language support: English, Spanish, French, German, Italian, Portuguese, Dutch, etc.
  • Efficient and lightweight: Small, fast, production-ready.
  • C/C++ API: Direct integration without heavyweight dependencies.
  • Portable: Works on embedded systems and servers alike.

Typical Use Cases​

  • Search indexing: Normalize word variants before building inverted indexes.
  • Query normalization: Reduce queries to stems to increase recall.
  • Text preprocessing: Useful when full lemmatization is unnecessary.
  • Cross-language retrieval: Consistent stemming across supported languages.

Industrial Fit​

Requirementlibstemmer Support
Term normalization (stemming)✔️
Multi-language stemming✔️
Lightweight integration✔️
Unicode normalization❌*
Lemmatization (morphology aware)❌

* libstemmer expects pretokenized words; full Unicode handling requires pre-processing.

C++ Usage Example​

#include <iostream>
#include <string>
#include <libstemmer.h>

int main() {
    struct sb_stemmer * stemmer = sb_stemmer_new("english", nullptr);
    if (!stemmer) return 1;

    std::string word = "running";
    const sb_symbol * stemmed = sb_stemmer_stem(stemmer,
                                                (const sb_symbol*)word.c_str(),
                                                word.size());
    if (stemmed)
        std::cout << "Original: " << word
                  << ", Stemmed: " << (char*)stemmed << std::endl;

    sb_stemmer_delete(stemmer);
    return 0;
}