I've seen these two different ways to cast an int to a double in C:
double double_var = (double) int_var;
double double_var = double(int_var);
What's the difference between these two methods? When should I use one over the other?
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Ben Lindsay
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4One is valid C, the other isn't. Neither is necessary, since `double double_var = int_var;` already has the desired behaviour. – Kerrek SB Feb 02 '16 at 01:38
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5The first is syntactically correct C. The second is syntactically invalid in C (but is correct in C++ and means the same as the first when written in C++ code). – Jonathan Leffler Feb 02 '16 at 01:38
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2.... Though, in C++ you try to avoid those vanilla casts and instead would rather write: ``static_cast
(int_var);`` – BitTickler Feb 02 '16 at 01:41
1 Answers
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As Jonathan Leffler stated, the first is from C and the second from C++:
The first one is a C-style cast; the second is the instantiation of a double by passing the constructor an int value.
So the second isn't really a cast but the creation of a new instance (So it is more C++ than C).
If you only do some C then using constructors isn't relevant (there is no Object Oriented Programming in C, that's a C++ feature).
If you're doing some C++ then you should avoid C-style casts (as @BitTickler stated) since problems can occure according the type of values you use it on. C++ provides several casts types for several cases.
See this answer for further informations.
