Difference between Typedef and Define...in C ?

[ngpbalaji]

whats the Difference between Typedef and Define in C?
we can Use both for the case below...

#define INT32 int

typedef int INT32;

for both the case actually what will happen when compiling and running?

And is there any specific use for typedef .. If yes give me Examples ?

Thanks & Regards
-Balaji

[RedSon]

I don't think you can do

#typedef lengthof(exp) ((sizeof((exp)) )/sizeof((*(exp)) ))

typedef only allows you to redefine types where as #define will let you define anything.

[JosAH]

whats the Difference between Typedef and Define in C?
we can Use both for the case below...

#define INT32 int

typedef int INT32;

for both the case actually what will happen when compiling and running?

And is there any specific use for typedef .. If yes give me Examples ?

Thanks & Regards
-Balaji

A #define is just a macro, i.e. it will be processed/expanded by the preprocessor.
When the actual C compiler starts doing its work there will be no sign of any
INT32 anymore. The typedef language facility is handled by the C compiler
itself: it introduces another name for a type. It's an awful hack actually: when
the C compiler parses that name in the right context the name is supposed
the alias for the type, otherwise it's supposed to be an identifier name:

typedef int t;
t t(t x) { int t; ... }

kind regards,

Jos

[ngpbalaji]

I don't think you can do

#typedef lengthof(exp) ((sizeof((exp)) )/sizeof((*(exp)) ))

typedef only allows you to redefine types where as #define will let you define anything.

The define will replace all the Macros before compile..but typedef will redefine types after compilation ...
Is it correct?
can u explain me on this?

[JosAH]

The define will replace all the Macros before compile..but typedef will redefine types after compilation ...
Is it correct?
can u explain me on this?

Correct about the #define part. A typedef is just a new name for an already
existing type. defines are handled by the preprocessor while typedefs are
handled by the C compiler itself.

kind regards,

Jos

[ngpbalaji]

Correct about the #define part. A typedef is just a new name for an already
existing type. defines are handled by the preprocessor while typedefs are
handled by the C compiler itself.

kind regards,

Jos

Thanks for the kind Reply...
Regards
Balaji

[mkyadav206]

1.The typedef is limited to giving symbolic names to types only where as #define can be used to define alias for values as well, like you can define 1 as ONE etc.

2.#define should not be terminated with semicolon, but typedef should be terminated with semicolon.

3.he typedef interpretation is performed by the compiler where as #define statements are processed by the pre-processor.

4. #define will just copy-paste the definition values at the point of use, while typedef is actual definition of a new type

5.typedef follows the scope rule which mean if a new type is defined in a scope(inside a function), then the new type name will only be visible till the scope is there.

Here I got exact answer.. Typedef vs Define in c

[Sherin]

Typedef :

A typedef defines a new name for existing types and does not introduce a new type. It is the (partial storage-class specifier) compiler directive mainly use with user-defined data types (structure, union or enum) to reduce their complexity and increase code readability and portability.

Syntax:

typedef type NewTypeName;

example

int main()
{
UnsignedInt data1, data2;

data1 = 100;

data2 = 200;

printf("%d %d ",data1,dat a2);

return 0;
}

Output: 100 200



define

A #define is a preprocessor directive and it replaces the value before compiling the code. One of the major problems with the macro that there is no type checking. Generally, the macro is used to create the alias, in C language macro is also used as a file guard.

example

int main()
{
printf("%d ", Value);

return 0;
}

Output: 10