CODEWITHSUNDEEP
ctypedef
Alex
Alex

Reputation: 10126

How can be size of variable guaranteed

I have variable that must be 16 bit long. How should I define it to be exactly 16 bit independently on the platform?

I can define it as short, but depending on the platform it can be 16 bits or more.

Upvotes: 0

Views: 119

Answers (4)

wildplasser
wildplasser

Reputation: 44240

if <stdint.h> and int16_t are not available, a workaround could be a bitfield. Since a bitfield is only valid inside a struct or union, it has to be wrapped into one:

#include <stdio.h>

struct auw {
    int sixteen :16;
        };

int main(void)
{

struct auw one = {16*1024 }, two, result;

two = one; /* assigmment is easy*/

        /* but addition is a bit more painful */
result.sixteen = one.sixteen + two.sixteen -1;

printf("Result=%d\n", (int) result.sixteen );

return 0;
}

Upvotes: 0

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272487

Assuming you're using C99, then use uint16_t (or int16_t) from <stdint.h>. These are guaranteed to exist so long as the compiler has an underlying 16-bit type available.

Upvotes: 6

Nithin Bhaskar
Nithin Bhaskar

Reputation: 726

If you want a portable unsigned 16-bit integer, use uint16_t and for signed 16-bit integer, use int16_t.

inttypes.h and stdint.h are both introduced in C99. If you are using C89, you have to define your own type.

Upvotes: 0

Yu Hao
Yu Hao

Reputation: 122383

Use int16_t for signed integer or uint16_t for unsigned, The header inttypes.h and stdint.h are introduced in C99. If you are using C89, define your own type.

Note that they may not be provided in certain implementation, according to C11(ISO/IEC 9899:201x) §7.20 Integer types

For each type described herein that the implementation provides) shall declare that typedef name and define the associated macros. Conversely, for each type described herein that the implementation does not provide, shall not declare that typedef name nor shall it define the associated macros. An implementation shall provide those types described as ‘‘required’’, but need not provide any of the others (described as ‘optional’’).

Upvotes: 1

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