| cdb | µVision Device Database |
| cdml | Claris Dynamic Markup Language Document |
| cdt | ProWorx NXT Temporary Long Comment Data |
| cdx | Alpha Five Table Index |
| cec | Windows CE Catalog Item |
| cel | CIMFast Event Language Source Code |
| cem | Windows CE Emulator Image |
| cetool | Windows CE Plugin |
| cfb | Microsoft Compound File Binary |
| cfc | ColdFusion Component File |
| cfm | ColdFusion Markup Language |
| cfml | ColdFusion Markup Language |
| cfo | Borland Turbo C Form Object |
| cga | CryENGINE Geometry Animation |
| cgf | CryENGINE Geometry Format Data |
| cgf | ProWorx NXT Codegen Batch |
| cgfx | Nvidia CgFX Shader |
| cgi | RAD Studio CodeGuard Configuration |
| cginc | Unity Custom Shader Include |
| cgl | RAD Studio CodeGuard Log |
| cgr | Quest3D Channel Group File |
| cgt | GOLD Parser Compiled Grammar Table |
| changes | Squeak Changes Data |
| chef | Chef Source Code |
| chi | C To Haskell Interface File |
| chs | Haskell Source With C Hooks |
| cic | Hitachi Ladder Editor Circuit Comment |
| ciq | CONNX InfoNaut Query |
| cjs | CommonJS Script |
| ck | ChucK Source Code |
| ckbx | Cricket Audio XML Bank Description |
| ckg | Kokogut C Output File |
| ckm | Creation Kit Macro |
| cko | Kokogut C Output File |
| cl | Lisp Source Code |