C++ Basic typedef syntax


A typedef declaration has the same syntax as a variable or function declaration, but it contains the word typedef. The presence of typedef causes the declaration to declare a type instead of a variable or function.

int T;         // T has type int
typedef int T; // T is an alias for int

int A[100];         // A has type "array of 100 ints"
typedef int A[100]; // A is an alias for the type "array of 100 ints"

Once a type alias has been defined, it can be used interchangeably with the original name of the type.

typedef int A[100];
// S is a struct containing an array of 100 ints
struct S {
    A data;

typedef never creates a distinct type. It only gives another way of referring to an existing type.

struct S {
    int f(int);
typedef int I;
// ok: defines int S::f(int)
I S::f(I x) { return x; }