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gmp_scanf
and friends accept format strings similar to the standard C
scanf
(see Formatted Input in The GNU C
Library Reference Manual). A format specification is of the form
% [flags] [width] [type] conv
GMP adds types ‘Z’, ‘Q’ and ‘F’ for mpz_t
, mpq_t
and mpf_t
respectively. ‘Z’ and ‘Q’ behave like integers.
‘Q’ will read a ‘/’ and a denominator, if present. ‘F’ behaves
like a float.
GMP variables don’t require an &
when passed to gmp_scanf
, since
they’re already “call-by-reference”. For example,
/* to read say "a(5) = 1234" */ int n; mpz_t z; gmp_scanf ("a(%d) = %Zd\n", &n, z); mpq_t q1, q2; gmp_sscanf ("0377 + 0x10/0x11", "%Qi + %Qi", q1, q2); /* to read say "topleft (1.55,-2.66)" */ mpf_t x, y; char buf[32]; gmp_scanf ("%31s (%Ff,%Ff)", buf, x, y);
All the standard C scanf
types behave the same as in the C library
scanf
, and can be freely intermixed with the GMP extensions. In the
current implementation the standard parts of the format string are simply
handed to scanf
and only the GMP extensions handled directly.
The flags accepted are as follows. ‘a’ and ‘'’ will depend on support from the C library, and ‘'’ cannot be used with GMP types.
*
read but don’t store a
allocate a buffer (string conversions) '
grouped digits, GLIBC style (not GMP types)
The standard types accepted are as follows. ‘h’ and ‘l’ are portable, the rest will depend on the compiler (or include files) for the type and the C library for the input.
h
short
hh
char
j
intmax_t
oruintmax_t
l
long int
,double
orwchar_t
ll
long long
L
long double
q
quad_t
oru_quad_t
t
ptrdiff_t
z
size_t
The GMP types are
F
mpf_t
, float conversionsQ
mpq_t
, integer conversionsZ
mpz_t
, integer conversions
The conversions accepted are as follows. ‘p’ and ‘[’ will depend on support from the C library, the rest are standard.
c
character or characters d
decimal integer e
E
f
g
G
float i
integer with base indicator n
characters read so far o
octal integer p
pointer s
string of non-whitespace characters u
decimal integer x
X
hex integer [
string of characters in a set
‘e’, ‘E’, ‘f’, ‘g’ and ‘G’ are identical, they all read either fixed point or scientific format, and either upper or lower case ‘e’ for the exponent in scientific format.
C99 style hex float format (printf %a
, see Formatted Output Strings) is always accepted for mpf_t
, but for the standard float
types it will depend on the C library.
‘x’ and ‘X’ are identical, both accept both upper and lower case hexadecimal.
‘o’, ‘u’, ‘x’ and ‘X’ all read positive or negative
values. For the standard C types these are described as “unsigned”
conversions, but that merely affects certain overflow handling, negatives are
still allowed (per strtoul
, see Parsing of
Integers in The GNU C Library Reference Manual). For GMP types there are
no overflows, so ‘d’ and ‘u’ are identical.
‘Q’ type reads the numerator and (optional) denominator as given. If the
value might not be in canonical form then mpq_canonicalize
must be
called before using it in any calculations (see Rational Number Functions).
‘Qi’ will read a base specification separately for the numerator and denominator. For example ‘0x10/11’ would be 16/11, whereas ‘0x10/0x11’ would be 16/17.
‘n’ can be used with any of the types above, even the GMP types. ‘*’ to suppress assignment is allowed, though in that case it would do nothing at all.
Other conversions or types that might be accepted by the C library
scanf
cannot be used through gmp_scanf
.
Whitespace is read and discarded before a field, except for ‘c’ and ‘[’ conversions.
For float conversions, the decimal point character (or string) expected is
taken from the current locale settings on systems which provide
localeconv
(see Locales and Internationalization in The GNU C Library Reference Manual). The C library will normally do the same
for standard float input.
The format string is only interpreted as plain char
s, multibyte
characters are not recognised. Perhaps this will change in the future.
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