CWEB

CWEB is a literate programming system designed for the C and C++ languages. It was created by Donald E. Knuth with Silvio Levy as an extension of the original WEB system, which Knuth developed for Pascal. CWEB enables programmers to write source code and its documentation in a single, integrated source file, emphasizing explanation and design alongside implementation.

In a CWEB file, the programmer writes prose and code blocks in a language called WEB. The source file typically uses the .w extension. The system provides two primary tools: cweave and ctangle. Cweave weaves the WEB file into a TeX document, producing richly formatted documentation that explains the program’s structure and algorithms. Ctangle tangles the same source into compilable C or C++ code. The workflow thus produces both a readable manual and a separate C/C++ source file suitable for compilation.

The approach reflects the literate programming philosophy: to tell the story of the program in human terms while presenting the actual code in a coherent, cross-referenced arrangement. CWEB supports sections, macros, and cross-references, enabling writers to organize material in a narrative order that may differ from the order of code fragments.

History and influence: CWEB originated in the 1990s as a C/C++ adaptation of Knuth’s WEB framework. While not as widely adopted as conventional C/C++ tooling today, it remains an influential example of literate programming and has influenced later systems such as Noweb. It is valued for its emphasis on documentation quality and the integration of description with code.