Troubleshooting

One of the common problems is link errors in the end of the build.

Be sure to set up the relevant environment variables that will allow the linker to find the libraries it needs (see below).

You're getting runtime errors like:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { code: -215, message: "OpenCV(4.2.0) /build/opencv/src/opencv-4.2.0/modules/highgui/src/window.cpp:384: error: (-215:Assertion failed) size.width>0 && size.height>0 in function \'imshow\'\n" }', src/libcore/result.rs:1188:5

thread 'extraction::tests::test_contour_matching' panicked at 'called `Result::unwrap()` on an `Err` value: Error { code: -215, message: "OpenCV(4.1.1) /tmp/opencv-20190908-41416-17rm3ol/opencv-4.1.1/modules/core/src/matrix_wrap.cpp:79: error: (-215:Assertion failed) 0 <= i && i < (int)vv.size() in function \'getMat_\'\n" }', src/libcore/result.rs:1165:5

These errors (note the .cpp source file and Error return value) are coming from OpenCV itself, not from the crate. It means that you're using the OpenCV API incorrectly, e.g. passing incompatible or unexpected arguments. Please refer to the OpenCV documentation for details.

You're getting errors that methods don't exist or not implemented for specific structs, but you can see them in the documentation and in the crate source.

Be sure to import use opencv::prelude::*;. The crate contains a lot of traits that need to be imported first.
On Windows, you're getting the (exit code: 0xc0000135, STATUS_DLL_NOT_FOUND) error when running the compiled binary.

That often means that Windows can't find the OpenCV or Clang library dll. Be sure to set up PATH environment variable correctly or copy the dll next to the binary you're trying to run (e.g. "C:\tools\opencv\build\x64\vc16\bin" and "C:\Program Files\LLVM\bin"). Check that guide too.
On Windows with VCPKG you're getting a lot of linking errors in multiple files like in this issue.

Make sure to add missing linked libs to OPENCV_LINK_LIBS environment variable prepended by +, e.g.:
```
OPENCV_LINK_LIBS="+user32,gdi32,comdlg32"
```
Alternatively, switch to the dynamic linking mode by having environment variable VCPKGRS_DYNAMIC set to "1".
On Windows with OpenCV 4.6.0 you're getting linking errors related to img_hash module like in this issue.

Be sure to add opencv_img_hash460 to your OPENCV_LINK_LIBS environment variable because it's being built as a separate file.
On macOS you're getting the dyld: Library not loaded: @rpath/libclang.dylib error during the build process.

OS can't find libclang.dylib dynamic library because it resides in a non-standard path, set up the DYLD_FALLBACK_LIBRARY_PATH environment variable to point to the path where libclang.dylib can be found, e.g. for Command Line Tools:
```
export DYLD_FALLBACK_LIBRARY_PATH="$(xcode-select --print-path)/usr/lib/"
```
or XCode:
```
export DYLD_FALLBACK_LIBRARY_PATH="$(xcode-select --print-path)/Toolchains/XcodeDefault.xctoolchain/usr/lib/"
```
You might be running into the issue on the recent macOS versions where this environment variable remains empty after setting, please check this issue for some workarounds.
You're getting the a `libclang` shared library is not loaded on this thread error during crate build.

Enable the clang-runtime feature. The reason for the issue is that some clang-sys crate can either link to the corresponding dynamic library statically or load it at runtime based on whether its feature runtime is enabled. If enabled this crate feature applies to all crates that depend on clang-sys even if they didn't explicitly enable that feature themselves (at least with Rust edition before 2021 and Cargo resolver before 2).
You're getting 'limits' file not found error during crate build.

This error is caused by the missing/invalid installation of C++ standard library (e.g. libstdc++ for GCC). To fix this make sure that the toolchain you're using has the corresponding C++ standard library. The toolchain is used through libclang, so to get useful diagnostic info run:
```
clang -E -x c++ - -v
```
Look for Selected GCC installation and #include <...> search starts here to get the sense of what system toolchain is used by clang. Refer to this issue for more fixes and workarounds.
Using a language server IDE on macOS you're getting dyld: Library not loaded error from rust-analyzer

Check this issue for some ready-made configurations for VSCode and Zed.

Reporting issues

If you still have trouble using the crate after going through the Troubleshooting steps please fill free to report it to the bugtracker.

When reporting an issue please state:

Operating system
The way you installed OpenCV: package, official binary distribution, manual compilation, etc.
OpenCV version
Attach the full output of the following command from your project directory:
```
RUST_BACKTRACE=full cargo build -vv
```

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