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Update c_api install docs for CMake build system (#4702)

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Summary:
Updates the C API installation documentation to reflect the current CMake-based build system.

## Changes
- Replace outdated make-based instructions with clear CMake commands
- Add step-by-step build instructions for both CPU and GPU configurations
- Update library names and example paths to match current build output
- Improve overall documentation clarity

Fixes https://github.com/facebookresearch/faiss/issues/2421

## Testing
Documentation-only change, no code modifications.

Pull Request resolved: https://github.com/facebookresearch/faiss/pull/4702

Reviewed By: trang-nm-nguyen

Differential Revision: D88662666

Pulled By: mnorris11

fbshipit-source-id: f210c8f98f76972a1ad1aff86e3a2e10ab40e991
This commit is contained in:
Murat Aslan
2025-12-08 20:28:22 -08:00
committed by meta-codesync[bot]
parent abc294419a
commit ac2e3abe38
1 changed files with 29 additions and 16 deletions
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c_api/INSTALL.md
+29 -16
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@@ -6,17 +6,25 @@ Faiss provides a pure C interface, which can subsequently be used either in pure
Compilation instructions
------------------------
The full contents of the pure C API are in the ["c_api"](c_api/) folder.
Please be sure to follow the instructions on [building the main C++ library](../INSTALL.md#step-1-compiling-the-c-faiss) first.
Include `-DFAISS_ENABLE_C_API=ON` to the cmake command.
The C API is built as part of the main Faiss build using CMake. From the root of the Faiss repository:
`make -C build`
``` shell
# Configure with C API enabled
$ cmake -B build -DFAISS_ENABLE_C_API=ON .
# Build
$ make -C build -j faiss_c
```
This builds the dynamic library "faiss_c", containing the full implementation of Faiss and the necessary wrappers for the C interface. It does not depend on libfaiss.a or the C++ standard library.
This builds the dynamic library `libfaiss_c.so` (or `.dylib` on macOS), containing the full implementation of Faiss and the necessary wrappers for the C interface.
To build the example program, you should run `make -C build example_c` at the top level of
the faiss repo. The example program will be in `build/c_api/example_c` .
To build the example program:
``` shell
$ make -C build -j example_c
```
The example program will be located at `build/c_api/example_c`.
Using the API
-------------
@@ -61,20 +69,19 @@ if (c) {
}
```
An example is included, which is built automatically for the target `all`. It can also be built separately:
`make bin/example_c`
An example is included and can be built as shown in the compilation instructions above.
Building with GPU support
-------------------------
For GPU support, a separate dynamic library in the "c_api/gpu" directory needs to be built.
For GPU support, configure CMake with both GPU and C API enabled:
`make`
``` shell
$ cmake -B build -DFAISS_ENABLE_GPU=ON -DFAISS_ENABLE_C_API=ON .
$ make -C build -j gpufaiss_c
```
The "gpufaiss_c" dynamic library contains the GPU and CPU implementations of Faiss, which means that
it can be used in place of "faiss_c". The same library will dynamically link with the CUDA runtime
and cuBLAS.
The `libgpufaiss_c.so` dynamic library contains both GPU and CPU implementations of Faiss, which means it can be used in place of `libfaiss_c.so`. This library dynamically links with the CUDA runtime and cuBLAS.
Using the GPU with the C API
----------------------------
@@ -101,4 +108,10 @@ c = faiss_index_cpu_to_gpu(gpu_res, 0, cpu_index, &gpu_index);
if (c) { /* ... */ }
```
A more complete example is available by the name `bin/example_gpu_c`.
To build the GPU example:
``` shell
$ make -C build -j example_gpu_c
```
The example program will be located at `build/c_api/gpu/example_gpu_c`.