Typedef - Using Typedef With Type Casts

Using Typedef With Type Casts

A typedef is created using type declaration syntax but can be used as if it were created using type cast syntax. (Type casting changes a data type.) For instance, in each line after the first line of:

typedef int (*funcptr)(double); // pointer to function of double returning int funcptr x = (funcptr) NULL; // C or C++ funcptr y = funcptr(NULL); // C or C++ funcptr z = static_cast(NULL); // C++ only

funcptr is used on the left-hand side to declare a variable and is used on the right-hand side to cast a value. Thus, typedefs can be used by programmers who do not wish to figure out how to convert declaration syntax to type cast syntax.

Note that, without the typedef, it is generally not possible to use declaration syntax and cast syntax interchangeably. For example:

void *p = NULL; int (*x)(double) = (int (*)(double)) p; // This is legal int (*)(double) y = (int (*)(double)) p; // Left-hand side is not legal int (*z)(double) = (int (*p)(double)); // Right-hand side is not legal

Famous quotes containing the words type and/or casts:

““... In truth I find it ridiculous that a man of his intelligence suffer over this type of person, who is not even interesting, for she is said to be foolish”, she added with all the wisdom of people who are not in love, who find that a sensible man should only be unhappy over a person who is worthwhile; it is almost tantamount to being surprised that anyone deign having cholera for having been infected with a creature as small as the vibrio bacilla.”
—Marcel Proust (1871–1922)

“Poets are the hierophants of an unapprehended inspiration; the mirrors of the gigantic shadows which futurity casts upon the present; the words which express what they understand not; the trumpets which sing to battle and feel not what they inspire; the influence which is moved not, but moves. Poets are the unacknowledged legislators of the world.”
—Percy Bysshe Shelley (1792–1822)