CODEWITHSUNDEEP
cmemory
Isaac Asante
Isaac Asante

Reputation: 465

Why does UINT_MAX return -1?

I've written the following program which seems to work well for what I need to do. However, I wonder why UINT_MAX is giving me -1 in the output (via printf()) and not 4294967295, as specified here: https://www.tutorialspoint.com/c_standard_library/limits_h.htm

#include <stdio.h>
#include <limits.h>

int main () {

printf("Below is the storage size for various data types.\n\n");

//char data type
printf("**char**\nStorage size: %d byte \t Minimum value: %d \t Maximum value: %d\n\n", sizeof(char), CHAR_MIN, CHAR_MAX);

//signed char data type
printf("**signed char**\nStorage size: %d byte \t Minimum value: %d \t Maximum value: %d\n\n", sizeof(signed char), SCHAR_MIN, SCHAR_MAX);

//unsigned char data type
printf("**unsigned char**\nStorage size: %d byte \t Maximum value: %d\n\n", sizeof(unsigned char), UCHAR_MAX);

//int data type
printf("**int**\nStorage size: %d bytes \t Minimum value: %d \t Maximum value: %d\n\n", sizeof(int), INT_MIN, INT_MAX);

//unsigned int data type
printf("**unsigned int**\nStorage size: %d bytes \t Maximum value: %d\n\n", sizeof(unsigned int), UINT_MAX);

}

Am I omitting a detail or misunderstanding something?

Upvotes: 0

Views: 3028

Answers (2)

J_S
J_S

Reputation: 3282

%d in the format string passed to printf means signed integer (for more information, see this link: http://www.cplusplus.com/reference/cstdio/printf/).

You're trying to format and print a maximum value of an unsigned integer as if it was a signed integer. Because signed integer cannot hold a maximum value of an unsigned integer (most significant bit is used for sign), it overflows and get start getting negative numbers.

If you modify your example to this:

printf("**unsigned int**\nStorage size: %zu bytes \t Maximum value: %u\n\n", sizeof(unsigned int), UINT_MAX);

it will give you the result you expect.

As also pointed out by others, %zu is the correct specifier for the result of sizeof.

Upvotes: 6

0___________
0___________

Reputation: 67709

Because you use %d which expects the signed int. use %u instead.

In Two's complement the -1 binary representation is the same as UINT_MAX

Upvotes: 2

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