Structs, Enums, and Typedefs in FFI Declarations
When working with PHP's Foreign Function Interface (FFI), you often need to interact with complex C types such as structs, enums, and typedefs. Declaring these types in FFI::cdef() allows you to mirror C data structures and constants within PHP, enabling direct manipulation and function calls that expect such types.
To declare a struct in FFI::cdef(), use the standard C syntax. Structs are defined with the struct keyword, listing all fields and their types. Enums are declared using the enum keyword, and can be embedded within structs or used as standalone types. Typedefs allow you to create aliases for existing types, which can simplify declarations and improve code clarity.
Internally, PHP represents these types as FFI CData objects. Structs become objects with properties for each field, enums are treated as integer constants, and typedefs simply act as alternate names for the aliased types. When you access a struct field or assign an enum value in PHP, the underlying memory layout matches the C definition, ensuring compatibility with native libraries.
ffi_struct_enum_typedef.php
12345678910111213141516171819202122232425262728<?php $ffi = FFI::cdef(' typedef unsigned int uint32_t; enum Color { RED = 1, GREEN = 2, BLUE = 3 }; typedef enum Color Color_t; struct Pixel { uint32_t x; uint32_t y; Color_t color; }; '); // Create a new Pixel struct $pixel = $ffi->new("struct Pixel"); $pixel->x = 10; $pixel->y = 20; $pixel->color = $ffi->enum("Color", "GREEN"); // Access struct fields and enum values echo "Pixel at ({$pixel->x}, {$pixel->y}) with color {$pixel->color}\n"; ?>
Common mistakes when working with these declarations include mismatching enum values between C and PHP, such as referencing an undefined constant or assigning an integer outside the enum's range. Another frequent issue is incorrect usage of typedefs, like confusing the alias with the original type name or redeclaring a typedef that already exists. Always ensure your typedefs match the expected signatures and your enums use valid values as defined in the C declaration. Proper alignment between your C definitions and PHP usage is essential for reliable FFI integration.
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Can you show me an example of declaring a struct, enum, or typedef in FFI::cdef()?
What are some best practices for keeping C and PHP definitions in sync?
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When working with PHP's Foreign Function Interface (FFI), you often need to interact with complex C types such as structs, enums, and typedefs. Declaring these types in FFI::cdef() allows you to mirror C data structures and constants within PHP, enabling direct manipulation and function calls that expect such types.
To declare a struct in FFI::cdef(), use the standard C syntax. Structs are defined with the struct keyword, listing all fields and their types. Enums are declared using the enum keyword, and can be embedded within structs or used as standalone types. Typedefs allow you to create aliases for existing types, which can simplify declarations and improve code clarity.
Internally, PHP represents these types as FFI CData objects. Structs become objects with properties for each field, enums are treated as integer constants, and typedefs simply act as alternate names for the aliased types. When you access a struct field or assign an enum value in PHP, the underlying memory layout matches the C definition, ensuring compatibility with native libraries.
ffi_struct_enum_typedef.php
12345678910111213141516171819202122232425262728<?php $ffi = FFI::cdef(' typedef unsigned int uint32_t; enum Color { RED = 1, GREEN = 2, BLUE = 3 }; typedef enum Color Color_t; struct Pixel { uint32_t x; uint32_t y; Color_t color; }; '); // Create a new Pixel struct $pixel = $ffi->new("struct Pixel"); $pixel->x = 10; $pixel->y = 20; $pixel->color = $ffi->enum("Color", "GREEN"); // Access struct fields and enum values echo "Pixel at ({$pixel->x}, {$pixel->y}) with color {$pixel->color}\n"; ?>
Common mistakes when working with these declarations include mismatching enum values between C and PHP, such as referencing an undefined constant or assigning an integer outside the enum's range. Another frequent issue is incorrect usage of typedefs, like confusing the alias with the original type name or redeclaring a typedef that already exists. Always ensure your typedefs match the expected signatures and your enums use valid values as defined in the C declaration. Proper alignment between your C definitions and PHP usage is essential for reliable FFI integration.
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