---
myst:
  html_meta:
    description: C10 core library API — fundamental types, device management, streams, and utilities used throughout PyTorch.
    keywords: PyTorch, C++, c10, core, Device, Stream, types
---

# C10: Core Utilities

C10 (Caffe2 + ATen = C10) is the core library that provides fundamental
utilities and data types used throughout PyTorch. It contains device
abstractions, memory management utilities, and common data structures.

**When to use C10:**

- When working with device-agnostic code (CPU, CUDA, XPU, etc.)
- When you need efficient array views without copying data
- When handling optional values or type-erased containers
- When writing code that needs to work across different PyTorch backends

**Basic usage:**

```cpp
#include <c10/core/Device.h>
#include <c10/util/ArrayRef.h>

// Device abstraction
c10::Device device(c10::kCUDA, 0);
if (device.is_cuda()) {
    std::cout << "Using CUDA device " << device.index() << std::endl;
}

// Efficient array views (no copy)
std::vector<int64_t> sizes = {3, 4, 5};
c10::ArrayRef<int64_t> sizes_ref(sizes);

// Optional values
c10::optional<int64_t> maybe_dim = 2;
int64_t dim = maybe_dim.value_or(-1);
```

## Header Files

- `c10/core/Device.h` - Device abstraction
- `c10/core/DeviceType.h` - Device type enumeration
- `c10/util/ArrayRef.h` - Non-owning array reference
- `c10/util/OptionalArrayRef.h` - Optional array reference
- `c10/util/Optional.h` - Optional value wrapper
- `c10/util/Half.h` - Half-precision float
- `c10/util/Exception.h` - Error checking macros (`TORCH_CHECK`, `TORCH_INTERNAL_ASSERT`, etc.)
- `c10/cuda/CUDAGuard.h` - CUDA device guards (see {doc}`../cuda/index`)
- `c10/cuda/CUDAStream.h` - CUDA stream management (see {doc}`../cuda/index`)
- `c10/xpu/XPUStream.h` - Intel XPU stream management
- `ATen/core/ivalue.h` - IValue for TorchScript interop

## C10 Categories

```{toctree}
:maxdepth: 1

device
guards
streams
types
utilities
```