9 <inttypes.h> More Integer Conversions

This header does conversions to maximum sized integers, division with maximum sized integers, and also provides format specifiers for printf() and scanf() for a variety of types defined in <stdint.h>.

The header <stdint.h> is included by this one.

9.1 Macros

These are to help with printf() and scanf() when you use a type such as int_least16_t… what format specifiers do you use?

Let’s start with printf()—all these macros start with PRI and then are followed by the format specifier you’d typically use for that type. Lastly, the number of bits is added on.

For example, the format specifier for a 64-bit integer is PRId64—the d is because you usually print integers with "%d".

An unsigned 16-bit integer could be printed with PRIu16.

These macros expand to string literals. We can take advantage of the fact that C automatically concatenates neighboring string literals and use these specifiers like this:

#include <stdio.h>     // for printf()
#include <inttypes.h>

int main(void)
{
    int16_t x = 32;

    printf("The value is %" PRId16 "!\n", x);
}

There’s nothing magical happening on line 8, above. Indeed, if I print out the value of the macro:

printf("%s\n", PRId16);

we get this on my system:

hd

which is a printf() format specifier meaning “short signed integer” .

So back to line 8, after string literal concatenation, it’s just as if I’d typed:

    printf("The value is %hd!\n", x);

Here’s a table of all the macros you can use for printf() format specifiers… substitute the number of bits for N, usually 8, 16, 32, or 64.

Note again how the lowercase center letter represents the usual format specifiers you’d pass to printf(): d, i, o, u, x, and X.

And we have a similar set of macros for scanf() for reading in these various types:

The rule is that for each type defined in <stdint.h> there will be corresponding printf() and scanf() macros defined here.

9.2 imaxabs()

Compute the absolute value of an intmax_t

Synopsis

#include <inttypes.h>

intmax_t imaxabs(intmax_t j);

Description

When you need the absolute value of the biggest integer type on the system, this is the function for you.

The spec notes that if the absolute value of the number cannot be represented, the behavior is undefined. This would happen if you tried to take the absolute value of the smallest possible negative number in a two’s-complement system.

Return Value

Returns the absolute value of the input, \(|j|\).

Example

#include <stdio.h>
#include <inttypes.h>

int main(void)
{
    intmax_t j = -3490;

    printf("%jd\n", imaxabs(j));    // 3490
}

See Also

fabs()

9.3 imaxdiv()

Compute the quotient and remainder of intmax_ts

Synopsis

#include <inttypes.h>

imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);

Description

When you want to do integer division and remainder in a single operation, this function will do it for you.

It computes numer/denom and numer%denom and returns the result in a structure of type imaxdiv_t.

This structure has two imaxdiv_t fields, quot and rem, that you use to retrieve the sought-after values.

Return Value

Returns an imaxdiv_t containing the quotient and remainder of the operation.

Example

#include <stdio.h>
#include <inttypes.h>

int main(void)
{
    intmax_t numer = INTMAX_C(3490);
    intmax_t denom = INTMAX_C(17);

    imaxdiv_t r = imaxdiv(numer, denom);

    printf("Quotient: %jd, remainder: %jd\n", r.quot, r.rem);
}

Output:

Quotient: 205, remainder: 5

See Also

remquo()

9.4 strtoimax() strtoumax()

Convert strings to types intmax_t and uintmax_t

Synopsis

#include <inttypes.h>

intmax_t strtoimax(const char * restrict nptr, char ** restrict endptr,
                   int base);

uintmax_t strtoumax(const char * restrict nptr, char ** restrict endptr,
                   int base);

Description

These work just like the strtol() family of functions, except they return an intmax_t or uintmax_t.

See the strtol() reference page for details.

Return Value

Returns the converted string as an intmax_t or uintmax_t.

If the result is out of range, the returned value will be INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX, as appropriate. And the errno variable will be set to ERANGE.

Example

The following example converts a base-10 number to an intmax_t. Then it attempts to convert an invalid base-2 number, catching the error.

#include <stdio.h>
#include <inttypes.h>

int main(void)
{
    intmax_t r;
    char *endptr;

    // Valid base-10 number
    r = strtoimax("123456789012345", &endptr, 10);

    if (*endptr != '\0')
        printf("Invalid digit: %c\n", *endptr);
    else
        printf("Value is %jd\n", r);
    
    // The following binary number contains an invalid digit
    r = strtoimax("0100102010101101", &endptr, 2);

    if (*endptr != '\0')
        printf("Invalid digit: %c\n", *endptr);
    else
        printf("Value is %jd\n", r);
}

Output:

Value is 123456789012345
Invalid digit: 2

See Also

strtol(), errno

9.5 wcstoimax() wcstoumax()

Convert wide strings to types intmax_t and uintmax_t

Synopsis

#include <stddef.h> // for wchar_t
#include <inttypes.h>

intmax_t wcstoimax(const wchar_t * restrict nptr,
                   wchar_t ** restrict endptr, int base);

uintmax_t wcstoumax(const wchar_t * restrict nptr,
                    wchar_t ** restrict endptr, int base);

Description

These work just like the wcstol() family of functions, except they return an intmax_t or uintmax_t.

See the wcstol() reference page for details.

Return Value

Returns the converted wide string as an intmax_t or uintmax_t.

If the result is out of range, the returned value will be INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX, as appropriate. And the errno variable will be set to ERANGE.

Example

The following example converts a base-10 number to an intmax_t. Then it attempts to convert an invalid base-2 number, catching the error.

#include <wchar.h>
#include <inttypes.h>

int main(void)
{
    intmax_t r;
    wchar_t *endptr;

    // Valid base-10 number
    r = wcstoimax(L"123456789012345", &endptr, 10);

    if (*endptr != '\0')
        wprintf(L"Invalid digit: %lc\n", *endptr);
    else
        wprintf(L"Value is %jd\n", r);
    
    // The following binary number contains an invalid digit
    r = wcstoimax(L"0100102010101101", &endptr, 2);

    if (*endptr != '\0')
        wprintf(L"Invalid digit: %lc\n", *endptr);
    else
        wprintf(L"Value is %jd\n", r);
}

Value is 123456789012345
Invalid digit: 2

See Also

wcstol(), errno