Q:

Initializing Malloc'ed structure

I am trying to initalize a structure using braces, but i am really trying to initalize the structure that is pointed to by a pointer returned from a malloc call.
typedef struct foo{
    int x;
    int y;
} foo;

foo bar = {5,6};

I understand how to do that, but i need to do it in this context.
foo * bar = malloc(sizeof(foo));
*bar = {3,4};

A:

(This was answered in comments, so making it a CW).
You need to cast the right-hand side of the assignment, like so:
*bar = (foo) {3,4};

As pointed out by @cremno in the comment, this isn't a cast but rather an assignment of a compound literal
The relevant section of the C99 standard is: 6.5.2.5 Compound literals which 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

