| cl | OpenCL Kernel |
| classpath | Eclipse IDE JAVA Project Classpath Data |
| clb | Code Librarian Database |
| clips | Coda Clips Data |
| clj | Clojure Source Code |
| cljc | Clojure Macros Code |
| cljs | ClojureScript Source Code |
| cljx | Clojure Portable Code |
| clog | MPI Parallel Environment CLOG |
| clojure | Clojure Source Code |
| cls | Visual Basic Class Module |
| clw | Clarion Source Code |
| clw | Visual Studio ClassWizard Data |
| cma | OCaml Library |
| cmake | CMake Script |
| cmbx | SharpDevelop Combine File |
| cmd | PTC Creo CL Commands Data |
| cmi | OCaml Compiled Interface |
| cml | ProWorx NXT Comment Data |
| cmn | Visual Studio Windows CE Build Settings |
| cmo | OCaml Compiled Bytecode |
| cmt | OCaml CMT Data |
| cmti | OCaml CMT Data |
| cmxa | OCaml Library |
| cnut | Squirrel Compiled Bytecode |
| cobol | Micro Focus COBOL Source Code |
| cod | µVision Complete Program Listing Data |
| codasite | Coda Site Data |
| cof | Common Object File |
| cof | MPLAB IDE COF File |
| coffee | CoffeeScript JavaScript File |
| conc | Concurnas Source Code |
| cos | Scilab Binary Diagram |
| cosf | Scilab ASCII Diagram |
| counter | NetObjects Fusion Components Bbscomp Message |