The differences between a class and a struct in C++ is: struct members and base classes/structs are public by default. class members and base classes/struts are private by default. Both classes and structs can have a mixture of public, protected and private members, can use inheritance and can have member functions. I would recommend you: … Read more
In (ANSI) C99, you can use a designated initializer to initialize a structure: MY_TYPE a = { .flag = true, .value = 123, .stuff = 0.456 }; Other members are initialized as zero: “Omitted field members are implicitly initialized the same as objects that have static storage duration.” (https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html)
The source referenced by the OP has some credibility …but what about Microsoft – what is the stance on struct usage? I sought some extra learning from Microsoft, and here is what I found: Consider defining a structure instead of a class if instances of the type are small and commonly short-lived or are commonly … Read more
[*] The common idiom is using both: typedef struct S { int x; } S; They are different definitions. To make the discussion clearer I will split the sentence: struct S { int x; }; typedef struct S S; In the first line you are defining the identifier S within the struct name space (not … Read more
In C++, there is only a subtle difference. It’s a holdover from C, in which it makes a difference. The C language standard (C89 §3.1.2.3, C99 §6.2.3, and C11 §6.2.3) mandates separate namespaces for different categories of identifiers, including tag identifiers (for struct/union/enum) and ordinary identifiers (for typedef and other identifiers). If you just said: … Read more
You forget the tricky 2nd difference between classes and structs. Quoth the standard (§11.2.2 in C++98 through C++11): In absence of an access-specifier for a base class, public is assumed when the derived class is declared struct and private is assumed when the class is declared class. And just for completeness’ sake, the more widely … Read more
Padding aligns structure members to “natural” address boundaries – say, int members would have offsets, which are mod(4) == 0 on 32-bit platform. Padding is on by default. It inserts the following “gaps” into your first structure: struct mystruct_A { char a; char gap_0[3]; /* inserted by compiler: for alignment of b */ int b; … Read more
Structs are value types which means they are copied when they are passed around. So if you change a copy you are changing only that copy, not the original and not any other copies which might be around. If your struct is immutable then all automatic copies resulting from being passed by value will be … Read more
This is because of padding added to satisfy alignment constraints. Data structure alignment impacts both performance and correctness of programs: Mis-aligned access might be a hard error (often SIGBUS). Mis-aligned access might be a soft error. Either corrected in hardware, for a modest performance-degradation. Or corrected by emulation in software, for a severe performance-degradation. In … Read more