In short, the order in which they are declared is the order in which they are laid out in memory, though exact alignment and padding is implementation defined (but there won't be any padding before the first member). To be precise, it's guaranteed that SomeType x; ((void*) &x) == ((void*) &x.field1). Why there would be padding before a member!

The C++ standard guarantees that memory layouts of a C struct and a C++ class (or struct -- same thing) will be identical, provided that the C++ class / struct fits the criteria of being POD ("Plain Old Data"). So what does POD mean? A class or struct is POD if:

In C#, struct 's memory is laid out by the compiler by default. The compiler can re-order data fields or pad additional bits between fields implicitly. So, I had to specify some special attribute to override this behavior for exact layout. AFAIK, C does not reorder or align memory layout of a struct by default.

A struct is another way to create a collection of data types in C. Unlike arrays, structs enable different data types to be grouped together. C stores a struct like a single-dimension array, where the data elements (fields) are stored contiguously.

Accessing structs. A struct is much like an array. The structure stores multiple data so you need to reference a specific member within the struct rather than the entire structure. use the . operator as in student.firstName or p1.x and p1.y

In memory, this struct is identical to a three-element array of longs--if rdi points to the struct s, then s.ID is at QWORD [rdi], grade is at QWORD [rdi+8], and s.awesome is at QWORD [rdi+16].

Regarding the memory layout, however, you have to consider memory alignment and consequent padding. On a 32bit machine, for instance, the struct could be laid out this way: myStruct + 0: valA [4 bytes] myStruct + 4: valB [4 bytes] myStruct + 8: valC [1 byte] padding [3 bytes]

There are several ways to obtain memory for an instance of your struct in C: using a global, static-lifetime struct, stack-allocating a local struct with automatic lifetime, or heap-allocating dynamic-lifetime memory to hold the struct.

Jun 29, 2023 · Structures allow us to combine several variables to create a new data type. Some other languages support the same concept but call it “records”. If you come from object-oriented programming you can think about them as classes without methods.

Dec 18, 2021 · Struct elements are contiguous in memory, so you could theoretically add the size of the first element to the address of the first element and get the second element, but often times there is padding between elements so you have to account for that as well. There are two general rules when counting structs and padding.