Package org.graalvm.nativeimage.c.struct

Annotation Interface CStruct

@Retention(RUNTIME) @Target(TYPE) public @interface CStruct
Denotes Java interface that imports a C struct. The interface must extend PointerBase, i.e., it is a word type. There is never a Java class that implements the interface.

Field accesses are done via interface methods that are annotated with CField, CFieldAddress, or CFieldOffset. All calls of the interface methods are replaced with the appropriate memory or address arithmetic operations. Here is an example to define a complex number structure: 

 @CStruct
 interface ComplexValue extends PointerBase {
     @CField("re")
     double realPart();

     @CField("re")
     void realPart(double re);

     @CField("im")
     double imagineryPart();

     @CField("im")
     void imagineryPart(double im);
 }
The annotated interface, or an outer class that contains the interface, must be annotated with CContext. Allocate an instances of the struct either by StackValue.get(java.lang.Class) or by UnmanagedMemory.malloc(org.graalvm.word.UnsignedWord). To access an array of structs one can define a special addressOf method: 

 @CStruct("int_double")
 interface IntOrDouble extends PointerBase {
     // allows access to individual structs in an array
     IntOrDouble addressOf(int index);

     @CField
     int i();

     @CField
     void i(int i);

     @CField
     double d();

     @CField
     void d(double d);

 }
Implementation of such method then allows one to do array arithmetics - e.g. obtain pointer to the first element of the array and then access the others: 

 private static double acceptIntIntDouble(IntOrDouble arr) {
     IntOrDouble firstInt = arr.addressOf(0);
     IntOrDouble secondInt = arr.addressOf(1);
     IntOrDouble thirdDouble = arr.addressOf(2);
     return firstInt.i() + secondInt.i() + thirdDouble.d();
 }

Since:
19.0
See Also:

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    Description
    boolean
    addStructKeyword
    Add the C "struct" keyword to the name specified in value().
    boolean
    isIncomplete
    If marked as incomplete, we will not try to determine the size of the struct.
    String
    value
    Specifies the name of the imported C struct type.

  • Element Details

    • value

      String value
      Specifies the name of the imported C struct type. If no name is provided, the type name is used as the struct name.
      Since:
      19.0
      Default:
      ""

    • isIncomplete

      boolean isIncomplete
      If marked as incomplete, we will not try to determine the size of the struct.
      Since:
      19.0
      Default:
      false

    • addStructKeyword

      boolean addStructKeyword
      Add the C "struct" keyword to the name specified in value().
      Since:
      19.0
      Default:
      false