You can use the function parse_printf_format to obtain
information about the number and types of arguments that are expected by
a given template string. This function permits interpreters that
provide interfaces to printf to avoid passing along invalid
arguments from the user’s program, which could cause a crash.
All the symbols described in this section are declared in the header file printf.h.
size_t parse_printf_format (const char *template, size_t n, int *argtypes) ¶Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | See POSIX Safety Concepts.
This function returns information about the number and types of
arguments expected by the printf template string template.
The information is stored in the array argtypes; each element of
this array describes one argument. This information is encoded using
the various ‘PA_’ macros, listed below.
The argument n specifies the number of elements in the array
argtypes. This is the maximum number of elements that
parse_printf_format will try to write.
parse_printf_format returns the total number of arguments required
by template. If this number is greater than n, then the
information returned describes only the first n arguments. If you
want information about additional arguments, allocate a bigger
array and call parse_printf_format again.
The argument types are encoded as a combination of a basic type and modifier flag bits.
int PA_FLAG_MASK ¶This macro is a bitmask for the type modifier flag bits. You can write
the expression (argtypes[i] & PA_FLAG_MASK) to extract just the
flag bits for an argument, or (argtypes[i] & ~PA_FLAG_MASK) to
extract just the basic type code.
Here are symbolic constants that represent the basic types; they stand for integer values.
PA_INT ¶This specifies that the base type is int.
PA_CHAR ¶This specifies that the base type is int, cast to char.
PA_STRING ¶This specifies that the base type is char *, a null-terminated string.
PA_POINTER ¶This specifies that the base type is void *, an arbitrary pointer.
PA_FLOAT ¶This specifies that the base type is float.
PA_DOUBLE ¶This specifies that the base type is double.
PA_LAST ¶You can define additional base types for your own programs as offsets
from PA_LAST. For example, if you have data types ‘foo’
and ‘bar’ with their own specialized printf conversions,
you could define encodings for these types as:
#define PA_FOO PA_LAST #define PA_BAR (PA_LAST + 1)
Here are the flag bits that modify a basic type. They are combined with the code for the basic type using inclusive-or.
PA_FLAG_PTR ¶If this bit is set, it indicates that the encoded type is a pointer to the base type, rather than an immediate value. For example, ‘PA_INT|PA_FLAG_PTR’ represents the type ‘int *’.
PA_FLAG_SHORT ¶If this bit is set, it indicates that the base type is modified with
short. (This corresponds to the ‘h’ type modifier.)
PA_FLAG_LONG ¶If this bit is set, it indicates that the base type is modified with
long. (This corresponds to the ‘l’ type modifier.)
PA_FLAG_LONG_LONG ¶If this bit is set, it indicates that the base type is modified with
long long. (This corresponds to the ‘L’ type modifier.)
PA_FLAG_LONG_DOUBLE ¶This is a synonym for PA_FLAG_LONG_LONG, used by convention with
a base type of PA_DOUBLE to indicate a type of long double.