Conversion Specifier Options

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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.

- Type: struct printf_info

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.