What is the difference between (type)value and type(value)?

Question

What is the difference between ``` (type)value ``` and ``` type(value) ``` in C++?

Accepted Answer

There is no difference; per the standard (§5.2.3):

A simple-type-specifier (7.1.5) followed by a parenthesized expression-list constructs a value of the specified type given the expression list. If the expression list is a single expression, the type conversion expression is equivalent (in definedness, and if defined in meaning) to the corresponding cast expression (5.4).

Since the question specified the difference between `type(value)` and `(type)value`, there is absolutely no difference.

If and only if you're dealing with a comma-separated list of values can there be a difference. In this case:

If the expression list specifies more than a single value, the type shall be a class with a suitably declared constructor (8.5, 12.1), and the expression T(x1, x2, ...) is equivalent in effect to the declaration T t(x1, x2, ...); for some invented temporary variable t, with the result being the value of t as an rvalue.

As Troubadour pointed out, there are a certain names of types for which the `type(value)` version simply won't compile. For example:

```
char *a = (char *)string;
```

will compile, but:

```
char *a = char *(string);
```

will not. The same type with a different name (e.g., created with a `typedef`) can work though:

```
typedef char *char_ptr;

char *a = char_ptr(string);
```

What is the difference between (type)value and type(value)?

Solution

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