Primitive types are small value types that are copied to the stack (or a CPU register) when you use them as function parameters or return values. You don’t need to pin or otherwise manage the lifespan of primitive types when calling unmanaged functions.
C# has different names for many primitive types compared to C and other languages. Refer to Platform invoke data types for a list of the unmanaged C language types that correspond to the managed C# types.
The following table shows the C type that each C# type marshals to by default. Default marshalling is a starting point, not a guarantee: it can vary by platform and by context (parameter, return value, or struct field). For example, System.Boolean marshals to a 4-byte value by default, and System.Char marshals according to the CharSet of the call. Use MarshalAsAttribute to control the exact representation when the default isn’t what you need.
Some examples include:
| C# base type | C# alias name | Unmanaged C type |
|---|---|---|
| System.Int32 | int | int32_t |
| System.Single | float | float |
| System.Char | char | char |
| System.Boolean | bool | int32_t |
| System.Byte | byte | unsigned char |
Note: Use fixed-width C types (such as int32_t from <stdint.h>) in your native code rather than int or long. The size of long in particular varies by platform: it’s 32-bit on Windows but 64-bit on most other desktop and mobile platforms. If the managed and unmanaged sides disagree about a type’s size, the data is corrupted.