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Conversion Specifier Options

If you define a meaning for %A, what if the template contains %+23A or %-#A? To implement a sensible meaning for these, the handler when called needs to be able to get the options specified in the template.

Both the handler-function and arginfo-function accept an argument that points to a struct printf_info, which contains information about the options appearing in an instance of the conversion specifier. This data type is declared in the header file printf.h.

struct printf_info Type
This structure is used to pass information about the options appearing in an instance of a conversion specifier in a printf template string to the handler and arginfo functions for that specifier. It contains the following members:
int prec
This is the precision specified. The value is -1 if no precision was specified. If the precision was given as *, the printf_info structure passed to the handler function contains the actual value retrieved from the argument list. But the structure passed to the arginfo function contains a value of INT_MIN, since the actual value is not known.
int width
This is the minimum field width specified. The value is 0 if no width was specified. If the field width was given as *, the printf_info structure passed to the handler function contains the actual value retrieved from the argument list. But the structure passed to the arginfo function contains a value of INT_MIN, since the actual value is not known.
wchar_t spec
This is the conversion specifier character specified. It's stored in the structure so that you can register the same handler function for multiple characters, but still have a way to tell them apart when the handler function is called.
unsigned int is_long_double
This is a boolean that is true if the L, ll, or q type modifier was specified. For integer conversions, this indicates long long int, as opposed to long double for floating point conversions.
unsigned int is_char
This is a boolean that is true if the hh type modifier was specified.
unsigned int is_short
This is a boolean that is true if the h type modifier was specified.
unsigned int is_long
This is a boolean that is true if the l type modifier was specified.
unsigned int alt
This is a boolean that is true if the # flag was specified.
unsigned int space
This is a boolean that is true if the flag was specified.
unsigned int left
This is a boolean that is true if the - flag was specified.
unsigned int showsign
This is a boolean that is true if the + flag was specified.
unsigned int group
This is a boolean that is true if the ' flag was specified.
unsigned int extra
This flag has a special meaning depending on the context. It could be used freely by the user-defined handlers but when called from the printf function this variable always contains the value 0.
unsigned int wide
This flag is set if the stream is wide oriented.
wchar_t pad
This is the character to use for padding the output to the minimum field width. The value is '0' if the 0 flag was specified, and ' ' otherwise.