| cspkg | Microsoft Azure Service Package |
| csq | Microsoft Visual FoxPro Client-Server Query File |
| csx | Visual C# Script |
| ctc | Visual Studio Command Table Configuration |
| ctf | MATLAB Component Technology File |
| ctl | Visual Basic User Control Text |
| cto | Visual Studio Binary Command Table Output |
| ctp | CakePHP Template |
| ctrace | Android System Trace Data |
| ctrl | Oracle WebLogic Workshop Controls |
| cts | ABC Permanent Locations Data |
| ctsym | Visual Studio Command Table Symbols File |
| ctx | Visual Basic User Control Binary File |
| ctxt | BlueJ Context File |
| cu | CUDA Source Code |
| cuf | Turbo C Utilities Form Definition |
| cuh | CUDA Header |
| cuo | CUDA Object |
| curl | Curl Applet |
| cv | Microsoft CodeView Data |
| cv4 | Microsoft CodeView Graphics Data |
| cvb | Borland Database Engine Internationalization Data |
| cvip | NI LabWindows/CVI Profiler Data |
| cvsignore | CVS Ignore File |
| cweb | CWEB Source Code |
| cwlink | CodeWarrior Link Data |
| cwproj | Clarion 7 Project |
| cwproj | C Omega Project |
| cx | Codemapper Script |
| cxx | C++ Source Code |
| d | D Source Code |
| d | GCC Dependency File |
| d4 | Dataphor Source Code |
| d4c | Dataphor Catalog Data |
| da | Gcov Data File |