auto data type

Can anyone explain me what is auto data type in C?

Thanks in advance

No.

There is no auto data type in C.

There is an auto keyword. It doesn't do anything, except perhaps explicitly state that you do not want the variable it applies to to be static.

From MSDN:

Quote:

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Originally Posted by http://msdn.microsoft.com/en-us/library/6k3ybftz(VS.80).aspx

auto Keyword

The auto storage-class specifier declares an automatic variable, a variable with a local lifetime. It is the default storage-class specifier for block-scoped variable declarations.

auto declarator ;

Remarks

An auto variable is visible only in the block in which it is declared. Declarations of auto variables can include initializers, as discussed in Initialization. Since variables with auto storage class are not initialized automatically, you should either explicitly initialize them when you declare them, or assign initial values to them in statements within the block. The values of uninitialized auto variables are undefined. (A local variable of auto or register storage class is initialized each time it comes in scope if an initializer is given.)

An internal static variable (a static variable with local or block scope) can be initialized with the address of any external or static item, but not with the address of another auto item, because the address of an auto item is not a constant.

Few programmers use the auto keyword in declarations because all block-scoped objects not explicitly declared with another storage class are implicitly automatic. Therefore, the following two declarations are equivalent:

Code:

---

// auto_keyword.cpp
int main()
{
  auto int i = 0;    // Explicitly declared as auto.
  int j = 0;    // Implicitly auto.
}

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I've often wondered why they even have an auto keyword? Are there ANY circumstances when you'd actually need to use it?

Well, C++ is going to use auto for variables whose type is automatically determined from the initialization:

Code:

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auto i = function_returning_enormously_complicated_templated_object();

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In C it probably wouldn't make much sense, since you won't have types which are mind-bogglingly complicated. So it's just a historic relict?

> So it's just a historic relict?
Or a futuristic relict :)

I once used a compiler that for whatever freaking reason did not automatically assume all locals are auto. So for all of the folks who wonder how come people are always spouting off about the standards for both C and C++, its little things like this that are where it all begins. I would hardly consider this a desireable behavior for a compiler to demonstrate.