How would you set a variable to the largest number possible in C?

Question

How would you set a variable to equal infinity (or any guaranteed largest number value) in C?

Answer 1

By far the simplest method to get the largest value for an unsigned integer type is to cast (-1) to that type. The standard (§6.2.5/9) requires that unsigned math be carried out modulo a number one greater than the largest value that can be represented, so for any unsigned type T, the expression ((T)-1) will necessarily be the largest value possible in that type.

Answer 2

#include <limits.h>
int x = INT_MAX;

EDIT: answered before the questioner clarified, I was just guessing what type they wanted.

Answer 3

Since there's a C++ tag on this question, I'll suggest numeric_limits:

#include <limits>

unsigned x = std::numeric_limits<unsigned>::max();

Answer 4

Another portable way to get maximum value of integer:

Unsigned integer

unsigned int uMax = (unsigned int)~0;

Signed integer

signed int iMax = (unsigned int)~0 >> 1;

Explanation

• ~0 -> setting all bits to one
• >> 1 -> erasing sign bit, by shifting all bits to the right by one position
• (unsigned int) typecasting to unsigned int after bits inversion instead of using ~0U, because C doesn't have a suffix for short,char literals (everything smaller than int in general)

So for biggest possible char value - just change in formula typecasting to unsigned char and etc.

Bonus - minimum value of signed int

Simply just invert all bits once more in max signed int expression:

signed int iMin = ~((unsigned int)~0 >> 1);

That sets first sign bit to one and the rest bits - to zero