Question: Where is the difference between %i and %d that are used in e.g. printf(), fscanf() and so on ? When do I have to use %i instead of %d and vice versa?

Although I do have the C99 Language Standard I don't know what is meant in the description of %i and %d.

Thank you for your help.

%d Matches an optionally signed decimal integer, whose format is the same as

expected for the subject sequence of the strtol function with the value 10

for the base argument. The corresponding argument shall be a pointer to

signed integer.

%i Matches an optionally signed integer, whose format is the same as expected

for the subject sequence of the strtol function with the value 0 for the

base argument. The corresponding argument shall be a pointer to signed

integer.

7.20.1.4 The strtol, strtoll, strtoul, and strtoull functions

Synopsis

1 #include <stdlib.h>

long int strtol(

const char * restrict nptr,

char ** restrict endptr,

int base);

long long int strtoll(

const char * restrict nptr,

char ** restrict endptr,

int base);

unsigned long int strtoul(

const char * restrict nptr,

char ** restrict endptr,

int base);

unsigned long long int strtoull(

const char * restrict nptr,

char ** restrict endptr,

int base);

Description

2 The strtol, strtoll, strtoul, and strtoull functions convert the initial

portion of the string pointed to by nptr to long int, long long int, unsigned

long int, and unsigned long long int representation, respectively. First,

they decompose the input string into three parts: an initial, possibly empty, sequence of

white-space characters (as specified by the isspace function), a subject sequence

resembling an integer represented in some radix determined by the value of base, and a

251) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round

to the same internal floating value, but if not will round to adjacent values.

§7.20.1.4 Library 309

ISO/IEC 9899:1999 (E) ŠISO/IEC

final string of one or more unrecognized characters, including the terminating null

character of the input string. Then, they attempt to convert the subject sequence to an

integer, and return the result.

3 If the value of base is zero, the expected form of the subject sequence is that of an

integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but

not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the

expected form of the subject sequence is a sequence of letters and digits representing an

integer with the radix specified by base, optionally preceded by a plus or minus sign,

but not including an integer suffix. The letters from a (or A) through z (or Z) are

ascribed the values 10 through 35; only letters and digits whose ascribed values are less

than that of base are permitted. If the value of base is 16, the characters 0x or 0X may

optionally precede the sequence of letters and digits, following the sign if present.

4 The subject sequence is defined as the longest initial subsequence of the input string,

starting with the first non-white-space character, that is of the expected form. The subject

sequence contains no characters if the input string is empty or consists entirely of white

space, or if the first non-white-space character is other than a sign or a permissible letter

or digit.

5 If the subject sequence has the expected form and the value of base is zero, the sequence

of characters starting with the first digit is interpreted as an integer constant according to

the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base

is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value

as given above. If the subject sequence begins with a minus sign, the value resulting from

the conversion is negated (in the return type). A pointer to the final string is stored in the

object pointed to by endptr, provided that endptr is not a null pointer.

6 In other than the "C" locale, additional locale-specific subject sequence forms may be

accepted.

7 If the subject sequence is empty or does not have the expected form, no conversion is

performed; the value of nptr is stored in the object pointed to by endptr, provided

that endptr is not a null pointer.

Returns

8 The strtol, strtoll, strtoul, and strtoull functions return the converted

value, if any. If no conversion could be performed, zero is returned. If the correct value

is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,

LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type

and sign of the value, if any), and the value of the macro ERANGE is stored in errno.