| 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 |
| cos | Scilab Binary Diagram |
| cosf | Scilab ASCII Diagram |
| counter | NetObjects Fusion Components Bbscomp Message |
| cox | Click and Create Extension Object |
| cpb | CPB Data |
| cpdsc | CMSIS Pack Project Description |
| cpf | Cab Provisioning Format |
| cphd | CloudChan Pre-processed Hypertext Document |
| cpk | Novell Netware Compiled Server Software Package |
| cplusplus | C++ Source Code |
| cpp | C++ Source Code |
| cpz | LoseThos C+ Source Code |
| cr | CRiSP Macro File |
| cr1 | CRBasic Source |
