.HH file extension
To open .HH files on Windows, right-click the .hh file → Open with → choose a code editor (for example, Visual Studio Code) to view/edit it as text.
To open a .hh file, use a code editor (for viewing/editing) or a C++ IDE (for editing with navigation and build integration). On Windows/macOS/Linux, apps like Visual Studio Code or other editors can open it as plain text.
Last updated: May 5, 2026 · Reviewed by Julian Stricker
Open on your device
Choose your operating system for a dedicated step-by-step opening guide.
How to open .HH files
Use these platform-specific instructions to open .HH files safely.
Windows
- Right-click the .hh file → Open with → choose a code editor (for example, Visual Studio Code) to view/edit it as text.
- If you have a C++ IDE installed, open it from the IDE (File → Open) to get code navigation and project context.
Mac
- Control-click the .hh file → Open With → choose a text/code editor to open it as plain text.
- If you use an IDE, open the file inside the IDE so it can interpret it as C++ header source.
Linux
- In your file manager, choose Open With → a text editor/IDE (many Linux desktops use shared-mime-info to decide the default).
- If the system opens it with the wrong app, set the default to a code editor for this file type.
iOS
- Open the file in Files and use a text/code editor app that can view plain text; if you need to compile or build, transfer it to a desktop C++ environment.
Android
- Open the file with a text editor app that can display plain text source; for development/build tasks, move it to a desktop IDE/toolchain.
Security notes
- .hh files are plain text source code, but they can still be risky if you compile or run code from an untrusted project—review the code and build scripts before executing anything.
- Treat unexpected .hh attachments with caution: a .hh file can be harmless text, but it may be part of a larger malicious codebase if combined with other files.
- If a server labels .hh with a generic or non-standard text MIME type, browsers and tools may handle it differently; avoid relying on automatic handling for security decisions.
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Can't open this file?
These are the most common causes and fixes when .HH files fail to open.
Common reasons
- It opens in the wrong application
- Garbled characters or missing line breaks
- Build errors after adding or editing the .hh file
Fix steps
- Use “Open with” and select a code editor/IDE to view it with proper syntax highlighting.
- Change the default app association for .hh files to your editor/IDE in your OS settings.
OS-specific troubleshooting
What is a .HH file?
.hh is a conventional filename extension for C++ header files that contain declarations and interfaces used by C++ source files. C/C++ toolchains generally do not require a specific header extension; .hh is often used by some projects to distinguish C++ headers from .h. The file contents are plain text C++ code.
Background
In many C++ codebases, header files contain declarations (such as function prototypes, class definitions, constants, and templates) that are included by implementation files during compilation. The .hh extension is one of several common conventions for C++ headers, alongside .h, .hpp, and others.
The C/C++ ecosystem does not mandate one extension for headers; compilers typically treat headers as text included by preprocessor directives, so naming is primarily a project or community convention. A frequently cited reason for .hh is to visually distinguish “C++ header” from “C header” in mixed-language projects.
On the web and in desktop MIME mapping databases, .hh may be associated with non-standard or environment-specific MIME types used for source code. This means browsers and servers may label it as a generic text type rather than a formally registered IANA media type for “C++ header.”
Common MIME types: text/x-c++hdr
Further reading
Authoritative resources for more details on the .HH format.
- HH - C++ Header File Format (FileFormat Docs)
- Stack Overflow: Reason why using ".hh" as extension for C++ header files
- IANA Media Types Registry (official list of standardized media types)
- MDN: Media types (MIME types) - HTTP
- Apache httpd mime.types mapping (shows common extension-to-type mappings, including .hh)
- Shared MIME-info Database specification (freedesktop.org standard used on Linux desktops)
Common .HH issues
It opens in the wrong application
Because .hh is plain text, the operating system may associate it with a generic text viewer or another program based on local MIME/extension mappings.
- Use “Open with” and select a code editor/IDE to view it with proper syntax highlighting.
- Change the default app association for .hh files to your editor/IDE in your OS settings.
Garbled characters or missing line breaks
The file may use an encoding your editor didn’t detect (for example, UTF-8 vs another encoding) or line-ending differences between platforms.
- In your editor, try changing the file encoding (commonly UTF-8) and line-ending mode (LF/CRLF).
- Re-download or re-export the file from the source repository to avoid copy/paste corruption.
Build errors after adding or editing the .hh file
Headers can cause compilation issues if include paths, include guards, or declarations don’t match the rest of the project.
- Ensure the header is referenced correctly by the project and that include paths are configured properly.
- Check for missing include guards or duplicate definitions and verify declarations match corresponding implementation files.
FAQ
Is .hh a “document” file?
Most commonly, no—.hh is used for C++ header source code (plain text). It’s typically opened with a code editor or IDE.
Is .hh different from .h or .hpp?
They’re all header-file conventions; C/C++ toolchains don’t require a particular extension. .hh is often used by some projects to signal “C++ header” vs “C header.”
What MIME type should .hh use?
There isn’t a single universally standardized IANA-registered MIME type specifically for .hh. Many systems use non-standard “x-” types for source files, and some common mime.types mappings associate .hh with text/x-c.
Can I convert a .hh file by renaming it to something else?
Renaming only changes the extension, not the content. If you need a different format, you must actually transform the content (for example, generate documentation) using appropriate tools.
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