Initialize struct without an assignment?

Question

I could not find an answer to this on the Internet, so here is my question: Can I define a struct instance without assigning it to a local or global variable in C? E.g.:

Answer 1

Yes C99 provides compound literals for this (see it live):

return (struct A) {  42 } ;

which is covered in the draft C99 standard section 6.5.2.5 Compound literals and says:

A postfix expression that consists of a parenthesized type name followed by a brace enclosed list of initializers is a compound literal. It provides an unnamed object whose value is given by the initializer list.⁸⁴⁾

and:

The value of the compound literal is that of an unnamed object initialized by the initializer list. If the compound literal occurs outside the body of a function, the object has static storage duration; otherwise, it has automatic storage duration associated with the enclosing block.

and provides several examples including:

EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects created using compound literals can be passed to functions without depending on member order:

drawline((struct point){.x=1, .y=1}, (struct point){.x=3, .y=4});

gcc also has a nice document on this in it's extension section since it supports this feature outside of C99 as well as clang.