This sequence is followed by optional type information. For integers this is one of l (long), ll (long long) or z (size_t). For strings this is one of L (ISO Latin 1), U (UTF-8) or W (wchar_t*).

Finally we come to the format specifier. This is one of

%
Emit the % character itself.

c
Emit a Unicode code point.

p
Emit a pointer.

d

i
Emit a a signed integer as decimal. The l (long), ll (long long) or z (size_t) denote the size.

o

u

x

X
Emit a a unsigned integer as octal, decimal or hexadecimal.

f

e

E

g

G
Emit a double.

s
Emit a 0-terminated string.

As
Emit a string as a Prolog atom, i.e., surrounded by single quotes and using the character escape syntax if that is needed to read the text back, e.g., SfprintfX(s, "%UAs", "a b") emits ’a b’. The string is 0-terminated unless the precision is given, in which case it is the length of the string in char or, for W, wchar_t elements. Unlike the other specifiers this one writes to s directly, which implies the field width does not apply to it. It is intended for the write() function of a blob; see section section 12.4.10.

Unlike the POSIX fprintf(), this function, and the related functions (Svprintf(), etc.) returns the number of characters written. Due to multibyte encodings the number of bytes written can be more. On error, it returns a negative value; in some cases there is extra information (e.g., in errno) but it cannot be relied on.

Each call to Sfprintf() is atomic in the sense that another thread that calls Sfprintf() on the same stream will block. If you wish to do a series of print statements without any other thread interleaving, you should call PL_acquire_stream() and use its returned IOSTREAM* value, then call PL_release_stream() at the end of the print statements.