I came across a new use of the keyword typedef in C++.
What does this typedef statement mean ?
int typedef foo;
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5Wow that's a new one. Is that portable? – Blindy Sep 20 '11 at 19:36
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1Yes..It is. I have tried it.It works as @Sven says – vivek Sep 20 '11 at 19:38
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1Adding this to the things I didn't expect to learn today archive – AJG85 Sep 20 '11 at 20:16
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1Adding this to the things that depress me about C++ archive – Russell Borogove Sep 20 '11 at 21:21
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8Add this to the list of never do this. – Martin York Sep 20 '11 at 22:34
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2possible duplicate of [C++ crazy typedef : what is the point of allowing this syntax by the Standard?](http://stackoverflow.com/questions/4422816/c-crazy-typedef-what-is-the-point-of-allowing-this-syntax-by-the-standard) – Nawaz Sep 21 '11 at 13:06
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1Another one: `int friend main();` (inside any class definition). – Kerrek SB Sep 22 '11 at 22:18
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@KerrekSB sometimes that has its uses: `friend int32_t ::globalFunction();` will be invalid because the `::` will take `int32_t` as a scope specifier. Writing it as `int32_t friend ::globalFunction();` makes it well-formed. – Johannes Schaub - litb May 30 '13 at 15:26
2 Answers
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It's the same as
typedef int foo;
i.e. it defines foo to be the type int. While the grammar allows to swap typedef and int in this case, you usually would not do this because it impairs readability.
Sven Marnach
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10Yes, because `typedef` is a *decl-specifier*, it can go before or after the type, just like `const`. Never noticed that before. – Ben Voigt Sep 20 '11 at 19:39
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1@Lambdageek That's **awesome** (though I won't ever use it, because of the `define`thing, and because it would just confuse the reader... function declaration typedefs are confusing enough...). – paercebal Sep 21 '11 at 08:00
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typedef is a decl-specifier, so it has the same syntax rules as const or static. It can be moved about like that and will mean the same thing.
Jonathan Grynspan
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3No, `typedef` and *storage-class-specifier* are both kinds of *decl-specifier*, but `typedef` is not a *storage-class-specifier*. – Ben Voigt Sep 20 '11 at 19:40