CODEWITHSUNDEEP
csizeintwidthbit
jayjay
jayjay

Reputation: 1047

finding the bit-width of an int in c; best-cross platform method

I need to know the width(size) of a native int in the system which my code is being run, in bits.

I can get the width in chars using "sizeof", however, it is my understanding that no-where in the C spec does a char have a specific number of bits assigned to it.

So what is the best cross platform method for finding the bit width of an int?

Upvotes: 2

Views: 960

Answers (3)

Fiddling Bits
Fiddling Bits

Reputation: 8861

Open up limits.h and you should see all the info you need about sizes on your particular platform's integer limits.

This is how you determine how many bits in an int:

#include <limits.h>
printf("Number of bits in an int: %zu\n", sizeof(int) * CHAR_BIT);

Open up float.h if you're interested in your particular platform's float and double limits.

Upvotes: 3

Martin R
Martin R

Reputation: 539765

CHAR_BIT (from <limits.h>) is the number of bits in a char, so 

sizeof(int) * CHAR_BIT

is what you are looking for.

CHAR_BIT is specified in "5.2.4.2.1 Sizes of integer types " of the C99 standard.

Added: It might be interesting that the Open Group specification

states:

The values for the limits {CHAR_BIT}, {SCHAR_MAX}, and {UCHAR_MAX} are now required to be 8, +127, and 255, respectively.

Upvotes: 8

0xFADE
0xFADE

Reputation: 832

I would be very amazed if anything didn't use 8 bits per character. You could fill a char with more then it should hold like 0xFFFF and see what it's value is.

Upvotes: 0

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