I've been struggling with accessing C structs from ruby. The problem is: I expose a struct from my framework (definition below). However when accessing/allocating it from ruby it seems the offsets are off by 4 bytes (as if macruby think it's supposed to be a double) Definition: #ifndef __SCRIPTINGBRIDGE__ union _vec3_t { float f[3]; struct { float x; float y; float z; }; struct { float r; float g; float b; }; struct { vec2_t xy; float andY; }; }; typedef union _vec3_t vec3_t; #else typedef struct _vec3_t { float x; float y; float z; } vec3_t; // Bridgesupport freaks out when given the above union so I show it a struct with the same layout #endif Example output: irb(main):001:0> framework "./GLMath.framework" => true irb(main):002:0> v1 = vec3_create(1,2,3) => #<vec3_t x=1.0 y=3.0 z=NaN> irb(main):003:0> v2 = v1.class.new(4,5,6) => #<vec3_t x=4.0 y=5.0 z=6.0> irb(main):004:0> printVec3(v1) 0x676f1310 - 0x676f1314 - 0x676f1318 Vec3: [1.00, 0.00, 3.00] => nil irb(main):005:0> printVec3(v2) 0x676f1310 - 0x676f1314 - 0x676f1318 Vec3: [4.00, 0.00, 5.00] => nil in the above example, vec3_create & printVec3 are C functions, shared using the scripting bridge. So when the struct is allocated from the c side, ruby only sees the first & last items, and the last item is on the offset of the second. when I then pass it to printVec3, it gets the first and last items only (last item taken from the place of the second item, => offsets are double what they should be). then when I allocate it using FFI in ruby, it's correcly read from the ruby side, but when I pass it to a c function, it gets the first item in the correct place, then the second item in the place of the last. The type definitions in my bridge support file are: <struct name='vec3_t' type='{_vec3_t="x"f"y"f"z"f}'/> <function name='vec3_create' inline='true'> <arg type='f'/> <arg type='f'/> <arg type='f'/> <retval type='{_vec3_t=fff}'/> </function> <function name='printVec3'> <arg type='{_vec3_t=fff}'/> </function> Right now I'm working around this by wrapping everything in an object on the objective-c side, but that is very slow and bloated. Has anyone ever gotten structs to work properly or know what is causing this? Note: if I return a pointer to the struct, and then assign to it's address using a boxed struct created from ruby, that works fine it seems. It's only if I return a struct directly. (However, myPointer[0].x = foo; would not work. I'd have to do a=myPointer[0];a.x=foo;myPointer[0]=a) – Fjölnir