按：寻寻觅觅了许久，终于找到了一个比较详细的版本，来源是sun公司的文档，应该都比较权威。原文见http://docs.sun.com/app/docs/doc/806-7023/6jfu564ks?l=zh_TW&a=view

NAME

printf, sprintf, snprintf, printerr- print formatted output

SYNOPSIS

$(NUCLEUS_DIR)/lib/embedded/libebd.s.a
#include <stdio.h>

int printf(const char * format, ... /* args */);
int sprintf(char * s, const char * format, ... /* args */);
int snprintf(char * s, size_t size, const char * format, ... /* args */);
int printerr(const char * format, ... /* args */);

API RESTRICTIONS

The function or functions documented here may not be used safely in all application contexts with all APIs provided in the ChorusOS 5.0 product.

See API(5FEA) for details.

DESCRIPTION

The printf() function sends output to the standard output channel, which is system defined. The printerr() function sends output to the standard error channel, which is system-defined. The sprintf() function sends output, followed by the null character ( \\0 ), in consecutive bytes starting at * s ; it is the user's responsibility to ensure that enough storage is available. Each function returns the number of characters transmitted (not including the \\0 in the case of sprintf() ), or a negative value if an output error was encountered.

The snprintf() function writes at most size-1 of the characters printed to the output string (the size character then gets the terminating zero). If the return value is greater than or equal to the size argument, the string was too short and some of the printed characters have been discarded.

Each of these functions converts, formats, and prints its arg s under control of the format .

The format has the general form:

%[flags] [width] [.precision] [{h | l | ll | q | L }]conversion_code

This format is a character string that contains two types of objects: plain characters, which are simply copied to the output channel, and conversion specifications, each of which results in obtaining zero or more arg s. The results are undefined if there are insufficient arg s for the format. If the format is exhausted while arg s remain, the excess arg s are simply ignored.

Flags

The flag characters and their meanings are:

-

The result of the conversion will be left-justified within the field.

+

The result of a signed conversion will always begin with a sign ( + or - ).

blank

If the first character of a signed conversion is not a sign, a blank will be prefixed to the result. This implies that if the blank and + flags both appear, the blank flag will be ignored.

#

This flag specifies that the value is to be converted to an ``alternate form.'' For c , d , s , and u conversions, the flag has no effect. For o conversion, it increases the precision to force the first digit of the result to be a zero. For x or X conversion, a non-zero result will have 0x or 0X prefixed to it. For e , E , f , g , and G conversions, the result will always contain a decimal point, even if no digits follow the point (normally, a decimal point appears in the result of these conversions only if a digit follows it). For g and G conversions, trailing zeroes will not be removed from the result (which they normally are).

Width

The width field is an optional decimal digit string specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded on the left (or right, if the left-adjustment flag `-', described above, has been set) to the field width. If the field width for an s conversion is preceded by a 0 , the string is right adjusted with zero-padding on the left.

The width field may be indicated by an asterisk ( * ) instead of a digit string. In this case, an integer arg supplies the field width or precision. The arg that is actually converted is not fetched until the conversion letter is seen, so the arg s specifying field width or precision must appear before the arg (if any) to be converted.

Precision

The precision field is an optional field that gives the minimum number of digits to appear for the d , o , u , x , or X conversions, the number of digits to appear after the decimal point for the e and f conversions, the maximum number of significant digits for the g conversion, or the maximum number of characters to be printed from a string in an s conversion. The precision takes the form of a dot ( . ) followed by a decimal digit string. A null digit string is treated as zero.

As for the width field, the precision field may be indicated by an asterisk (*). The meaning is the same as in the width field above.

Argument Size

An optional h , l (ell), q , or ll (ell ell) specifies the expected size of the actual argument for the d , i , o , u , x or X conversion codes. Ignored if specified before any other conversion code.

Their meanings are:

h

The argument is a short integer.

l

The argument is a long integer.

q

The argument is a quad integer.

ll

The argument is a long long integer.

An optional l (ell), or L specifies the expected size of the actual argument for the e , f , or g conversion codes.

They are ignored if specified before any other conversion code.

Their meanings are:

l

The argument is a double.

L

The argument is a long double.

Conversion Codes

The conversion characters and their meanings are:

d , i , o , u , x , X

The integer arg is converted to signed decimal ( d or i ), unsigned octal ( o ), decimal ( u ), or hexadecimal notation ( x and X ), respectively. The letters abcdef are used for x conversion and the letters ABCDEF for X conversion. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeroes. (For compatibility with older versions, padding with leading zeroes may alternatively be specified by prepending a zero to the field width. This does not imply an octal value for the field width.) The default precision is 1. The result of converting a zero value with a precision of zero is a null string.

D,O,U

These notations are semantically equivalent to, respectively, ld , lo , lu .

n

The arg should be a pointer to an integer into which is written the number of bytes written to the standard output I/O stream so far by this call. No argument is converted.

p

The arg should be a pointer to void. The value of the pointer is converted to a set of sequences of printable characters.

f

The float or double arg is converted to decimal notation in the style ``[ - ]ddd . ddd,'' where the number of digits after the decimal point is equal to the precision specification. If the precision is not specified, six digits are output; if the precision is explicitly 0, no decimal point appears.

e , E

The float or double arg is converted in the style ``[ - ]d . ddd e+- dd,'' where there is one digit before the decimal point and the number of digits after it is equal to the precision. If the precision is not specified, six digits are produced; if the precision is explicitly 0, no decimal point appears. The E format code will produce a number with E instead of e introducing the exponent. The exponent always contains at least two digits.

g , G

The float or double arg is printed in style f or e (or in style E in the case of a G format code), with the precision specifying the number of significant digits. The style used depends on the value converted: style e will be used only if the exponent resulting from the conversion is less than -4 or greater than the precision. Trailing zeroes are removed from the result; a decimal point appears only if it is followed by a digit.

c

The character arg is printed.

s

The arg is taken to be a string (character pointer) and characters from the string are printed until a null character ( \\0 ) is encountered, or until the number of characters indicated by the precision specification is reached. If the precision is not specified, it is assumed to be infinite and all characters up to the first null character are printed. A NULL value for arg will yield undefined results.

%

Print a % ; no argument is converted.

A non-existent or small field width will never cause truncation of a field; if the result of a conversion is wider than the field width, the field is simply expanded to contain the conversion result. Characters generated by printf() are printed in the same way as if putchar (3STDC) had been called.

Each conversion specification is introduced by the character % . After the % , the following appear in sequence:

• Zero or more flags , which modify the meaning of the conversion specification.

• An optional decimal digit string specifying a minimum field width . If the converted value has fewer characters than the field width, it will be padded on the left (or right, if the left-adjustment flag ` &ndash ;', described below, has been set) to the field width. If the field width for an s conversion is preceded by a 0, the string is right-adjusted with zero-padding on the left.

• An optional l (ell) specifying that a following d , o , u , x , or X conversion character applies to a long integer arg . An l before any other conversion character is ignored.

• A character that indicates the type of conversion to be applied.

EXAMPLES

To print a date and time in the form ``Sunday, July 3, 10:02,'' where weekday and month are pointers to null-terminated strings:

printf("%s, %s %d, %d:%.2d", weekday, month, day, hour, min);

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Evolving