What is the CXX file format?
A .cxx file is a C++ source code file - plain text containing compilable C++ language source. It is one of several recognized source extensions alongside .cpp, .cc, and .c++, all treated identically by compilers.
The file holds preprocessor directives (#include, #define, #ifdef), class and function definitions, template specializations, and (in an executable program) a main() entry point. Encoding is plain ASCII or UTF-8; an optional UTF-8 BOM (EF BB BF) may appear at the start but is not required.
The .cxx name is a spelling convention: the letter x substitutes for + twice, producing an ASCII-safe alternative to .c++. It is the preferred extension in certain scientific and visualization codebases - notably VTK, ITK, and some CMake-heavy projects - and was common in early Unix C++ toolchains.
All major compilers recognize .cxx natively:
- GCC (
g++) and Clang treat it as C++ without extra flags - MSVC recognizes
.cxxas C++ source - CMake, GNU Make, and Meson detect it automatically
The file stores no version metadata; the target C++ standard (C++98 through C++23) is specified as a compiler flag such as --std=c++17. The compiled output is an object file (.o or .obj) linked into an executable or library.
Security & safety
RISK: LOWA .cxx file is plain text and cannot run on its own - opening in an editor is safe. Risk only arises when you COMPILE and RUN unknown C++ code: source from untrusted origins can do anything a program can once built. Read code before compiling it; build untrusted code in a sandbox/VM.
Format details
in a nutshellPrograms that open CXX files
Windows5 apps
Microsoft Visual Studio
Freemium Add the .cxx to a C++ project and press Build/Run; the free Community edition includes the MSVC compiler. 
Notepad
Open-source Open the .cxx to read/edit with C++ syntax highlighting (viewing/editing only - no compiler). 
Visual Studio Code
Free Open the .cxx for syntax-highlighted editing; add the C/C++ extension + a compiler (MSVC or MinGW g++) to build and debug. 
C++ Builder (Embarcadero)
Freemium Add the .cxx to a C++ Builder project and build. Accepts .cxx as C++ source. 
macOS2 apps
Apple Xcode (Apple Clang)
Free Add the .cxx to an Xcode project, or from Terminal: 'clang++ hello.cxx -o hello && ./hello'.
Visual Studio Code
Free Edit the .cxx with the C/C++ extension; compile with Clang from the Xcode command-line tools. 
Linux3 apps
GCC / g++ (GNU Compiler Collection)
Open-source Compile from a terminal: 'g++ hello.cxx -o hello && ./hello'. Pre-installed or one package away on every distro.
GNU Emacs / Vim
Open-source Open the .cxx in the terminal editor to read/edit with C++ highlighting; pair with g++/make/cmake to build.
Visual Studio Code
Free Cross-platform editor with C/C++ extension; edits, builds (via g++/clang++) and debugs .cxx files. Technical details
deep spec| File encoding | Plain text; ASCII or UTF-8 (optional UTF-8 BOM at offset 0) |
| Binary signature | None - identified by file extension and content, not magic bytes |
| MIME type | text/x-c++src (alt: text/x-c++, text/plain) |
| Typical file size | A few KB to tens of KB per source file |
| Target C++ standard | C++98 through C++23; specified at compile time via flag (e.g., --std=c++17) |
| Extension meaning | Alphanumeric spelling of C++: x substitutes for + twice, yielding an ASCII-safe alternative to .c++ |
| Compiled output | Object file (.o or .obj); linked into an executable or shared library |
| Compiler support | GCC (g++), Clang, and MSVC all recognize .cxx as C++ source natively without extra flags |
| Build system support | CMake, GNU Make, and Meson detect .cxx as C++ automatically without extra configuration |
| Typical file content | #include directives, class/struct definitions, function bodies, template specializations, main() entry point |
| Comment syntax | Line comments (//) and block comments (/* */) |
| Header counterpart | .hxx or .hpp files hold declarations; .cxx files hold the matching definitions |
| Related source extensions | .cpp (Windows/cross-platform standard), .cc (GNU/Google style), .c++ (rare), .C (historical Unix) |
| Released | C++ created 1979-1985 (Bjarne Stroustrup, Bell Labs); .cxx is a long-standing extension convention |
| Latest version | ISO/IEC 14882:2024 (C++23); C++26 in progress |
| Open standard | Yes · royalty-free |
| Specification | isocpp.org |
CXX conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about CXX files.
