Development repo for 42cursus' ft_printf project
Man with references only to the used function (everything was deleted)
PRINTF(3)
PRINTF(3) BSD Library Functions Manual PRINTF(3)
NAME
printf -- formatted output conversion
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
int
printf(const char * restrict format, ...);
#include <stdarg.h>
DESCRIPTION
The printf() family of functions produces output according to a format as described below. The printf() and vprintf() functions
write output to stdout, the standard output stream; fprintf() and vfprintf() write output to the given output stream; dprintf() and
vdprintf() write output to the given file descriptor; sprintf(), snprintf(), vsprintf(), and vsnprintf() write to the character
string str; and asprintf() and vasprintf() dynamically allocate a new string with malloc(3).
Extended locale versions of these functions are documented in printf_l(3). See xlocale(3) for more information.
These functions write the output under the control of a format string that specifies how subsequent arguments (or arguments accessed
via the variable-length argument facilities of stdarg(3)) are converted for output.
The asprintf() and vasprintf() functions set *ret to be a pointer to a buffer sufficiently large to hold the formatted string. This
pointer should be passed to free(3) to release the allocated storage when it is no longer needed. If sufficient space cannot be
allocated, asprintf() and vasprintf() will return -1 and set ret to be a NULL pointer.
The snprintf() and vsnprintf() functions will write at most size-1 of the characters printed into the output string (the size'th
character then gets the terminating `\0'); if the return value is greater than or equal to the size argument, the string was too
short and some of the printed characters were discarded. The output is always null-terminated, unless size is 0.
The sprintf() and vsprintf() functions effectively assume a size of INT_MAX + 1.
For those routines that write to a user-provided character string, that string and the format strings should not overlap, as the
behavior is undefined.
The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged to the output
stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion speci-
fication is introduced by the % character. The arguments must correspond properly (after type promotion) with the conversion speci-
fier. After the %, the following appear in sequence:
o An optional field, consisting of a decimal digit string followed by a $, specifying the next argument to access. If this field
is not provided, the argument following the last argument accessed will be used. Arguments are numbered starting at 1. If
unaccessed arguments in the format string are interspersed with ones that are accessed the results will be indeterminate.
o Zero or more of the following flags:
`#' The value should be converted to an ``alternate form''. For c, d, i, n, p, s, and u conversions, this option has
no effect. For o conversions, the precision of the number is increased to force the first character of the output
string to a zero. For x and X conversions, a non-zero result has the string `0x' (or `0X' for X conversions)
prepended to it. For a, A, e, E, f, F, g, and G conversions, the result will always contain a decimal point, even
if no digits follow it (normally, a decimal point appears in the results of those conversions only if a digit fol-
lows). For g and G conversions, trailing zeros are not removed from the result as they would otherwise be.
`0' (zero) Zero padding. For all conversions except n, the converted value is padded on the left with zeros rather than
blanks. If a precision is given with a numeric conversion (d, i, o, u, i, x, and X), the 0 flag is ignored.
`-' A negative field width flag; the converted value is to be left adjusted on the field boundary. Except for n con-
versions, the converted value is padded on the right with blanks, rather than on the left with blanks or zeros. A
- overrides a 0 if both are given.
` ' (space) A blank should be left before a positive number produced by a signed conversion (a, A, d, e, E, f, F, g, G, or i).
`+' A sign must always be placed before a number produced by a signed conversion. A + overrides a space if both are
used.
`'' (apostrophe)
Decimal conversions (d, u, or i) or the integral portion of a floating point conversion (f or F) should be grouped
and separated by thousands using the non-monetary separator returned by localeconv(3).
o An optional separator character ( , | ; | : | _ ) used for separating multiple values when printing an AltiVec or SSE vector,
or other multi-value unit.
NOTE: This is an extension to the printf() specification. Behaviour of these values for printf() is only defined for operating
systems conforming to the AltiVec Technology Programming Interface Manual. (At time of writing this includes only Mac OS X 10.2
and later.)
o 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 with spaces on the left (or right, if the left-adjustment flag has been given) to fill out the field
width.
o An optional precision, in the form of a period . followed by an optional digit string. If the digit string is omitted, the pre-
cision is taken as zero. This gives the minimum number of digits to appear for d, i, o, u, x, and X conversions, the number of
digits to appear after the decimal-point for a, A, e, E, f, and F conversions, the maximum number of significant digits for g
and G conversions, or the maximum number of characters to be printed from a string for s conversions.
o An optional length modifier, that specifies the size of the argument. The following length modifiers are valid for the d, i, n,
o, u, x, or X conversion:
Modifier d, i o, u, x, X n
hh signed char unsigned char signed char *
h short unsigned short short *
l (ell) long unsigned long long *
ll (ell ell) long long unsigned long long long long *
j intmax_t uintmax_t intmax_t *
t ptrdiff_t (see note) ptrdiff_t *
z (see note) size_t (see note)
q (deprecated) quad_t u_quad_t quad_t *
Note: the t modifier, when applied to a o, u, x, or X conversion, indicates that the argument is of an unsigned type equivalent
in size to a ptrdiff_t. The z modifier, when applied to a d or i conversion, indicates that the argument is of a signed type
equivalent in size to a size_t. Similarly, when applied to an n conversion, it indicates that the argument is a pointer to a
signed type equivalent in size to a size_t.
The following length modifier is valid for the a, A, e, E, f, F, g, or G conversion:
Modifier a, A, e, E, f, F, g, G
l (ell) double (ignored, same behavior as without it)
L long double
The following length modifier is valid for the c or s conversion:
Modifier c s
l (ell) wint_t wchar_t *
The AltiVec Technology Programming Interface Manual also defines five additional length modifiers which can be used (in place of
the conventional length modifiers) for the printing of AltiVec or SSE vectors:
v Treat the argument as a vector value, unit length will be determined by the conversion specifier (default = 16 8-bit
units for all integer conversions, 4 32-bit units for floating point conversions).
vh, hv Treat the argument as a vector of 8 16-bit units.
vl, lv Treat the argument as a vector of 4 32-bit units.
NOTE: The vector length specifiers are extensions to the printf() specification. Behaviour of these values for printf() is only
defined for operating systems conforming to the AltiVec Technology Programming Interface Manual. (At time of writing this
includes only Mac OS X 10.2 and later.)
As a further extension, for SSE2 64-bit units:
vll, llv Treat the argument as a vector of 2 64-bit units.
o A character that specifies the type of conversion to be applied.
A field width or precision, or both, may be indicated by an asterisk `*' or an asterisk followed by one or more decimal digits and a
`$' instead of a digit string. In this case, an int argument supplies the field width or precision. A negative field width is
treated as a left adjustment flag followed by a positive field width; a negative precision is treated as though it were missing. If
a single format directive mixes positional (nn$) and non-positional arguments, the results are undefined.
The conversion specifiers and their meanings are:
diouxX The int (or appropriate variant) argument is converted to signed decimal (d and i), unsigned octal (o), unsigned decimal
(u), or unsigned hexadecimal (x and X) notation. The letters ``abcdef'' are used for x conversions; the letters ``ABCDEF''
are used for X conversions. The precision, if any, gives the minimum number of digits that must appear; if the converted
value requires fewer digits, it is padded on the left with zeros.
DOU The long int argument is converted to signed decimal, unsigned octal, or unsigned decimal, as if the format had been ld, lo,
or lu respectively. These conversion characters are deprecated, and will eventually disappear.
eE The double argument is rounded and converted in the style [-]d.ddde+-dd where there is one digit before the decimal-point
character and the number of digits after it is equal to the precision; if the precision is missing, it is taken as 6; if the
precision is zero, no decimal-point character appears. An E conversion uses the letter `E' (rather than `e') to introduce
the exponent. The exponent always contains at least two digits; if the value is zero, the exponent is 00.
For a, A, e, E, f, F, g, and G conversions, positive and negative infinity are represented as inf and -inf respectively when
using the lowercase conversion character, and INF and -INF respectively when using the uppercase conversion character. Sim-
ilarly, NaN is represented as nan when using the lowercase conversion, and NAN when using the uppercase conversion.
fF The double argument is rounded and converted to decimal notation in the style [-]ddd.ddd, where the number of digits after
the decimal-point character is equal to the precision specification. If the precision is missing, it is taken as 6; if the
precision is explicitly zero, no decimal-point character appears. If a decimal point appears, at least one digit appears
before it.
gG The double argument is converted in style f or e (or F or E for G conversions). The precision specifies the number of sig-
nificant digits. If the precision is missing, 6 digits are given; if the precision is zero, it is treated as 1. Style e is
used if the exponent from its conversion is less than -4 or greater than or equal to the precision. Trailing zeros are
removed from the fractional part of the result; a decimal point appears only if it is followed by at least one digit.
aA The double argument is rounded and converted to hexadecimal notation in the style [-]0xh.hhhp[+-]d, where the number of dig-
its after the hexadecimal-point character is equal to the precision specification. If the precision is missing, it is taken
as enough to represent the floating-point number exactly, and no rounding occurs. If the precision is zero, no hexadecimal-
point character appears. The p is a literal character `p', and the exponent consists of a positive or negative sign fol-
lowed by a decimal number representing an exponent of 2. The A conversion uses the prefix ``0X'' (rather than ``0x''), the
letters ``ABCDEF'' (rather than ``abcdef'') to represent the hex digits, and the letter `P' (rather than `p') to separate
the mantissa and exponent.
Note that there may be multiple valid ways to represent floating-point numbers in this hexadecimal format. For example,
0x1.92p+1, 0x3.24p+0, 0x6.48p-1, and 0xc.9p-2 are all equivalent. The format chosen depends on the internal representation
of the number, but the implementation guarantees that the length of the mantissa will be minimized. Zeroes are always rep-
resented with a mantissa of 0 (preceded by a `-' if appropriate) and an exponent of +0.
C Treated as c with the l (ell) modifier.
c The int argument is converted to an unsigned char, and the resulting character is written.
If the l (ell) modifier is used, the wint_t argument shall be converted to a wchar_t, and the (potentially multi-byte)
sequence representing the single wide character is written, including any shift sequences. If a shift sequence is used, the
shift state is also restored to the original state after the character.
S Treated as s with the l (ell) modifier.
s The char * argument is expected to be a pointer to an array of character type (pointer to a string). Characters from the
array are written up to (but not including) a terminating NUL character; if a precision is specified, no more than the num-
ber specified are written. If a precision is given, no null character need be present; if the precision is not specified,
or is greater than the size of the array, the array must contain a terminating NUL character.
If the l (ell) modifier is used, the wchar_t * argument is expected to be a pointer to an array of wide characters (pointer
to a wide string). For each wide character in the string, the (potentially multi-byte) sequence representing the wide char-
acter is written, including any shift sequences. If any shift sequence is used, the shift state is also restored to the
original state after the string. Wide characters from the array are written up to (but not including) a terminating wide
NUL character; if a precision is specified, no more than the number of bytes specified are written (including shift
sequences). Partial characters are never written. If a precision is given, no null character need be present; if the pre-
cision is not specified, or is greater than the number of bytes required to render the multibyte representation of the
string, the array must contain a terminating wide NUL character.
p The void * pointer argument is printed in hexadecimal (as if by `%#x' or `%#lx').
n The number of characters written so far is stored into the integer indicated by the int * (or variant) pointer argument. No
argument is converted. The format argument must be in write-protected memory if this specifier is used; see SECURITY
CONSIDERATIONS below.
% A `%' is written. No argument is converted. The complete conversion specification is `%%'.
The decimal point character is defined in the program's locale (category LC_NUMERIC).
In no case does a non-existent or small field width cause truncation of a numeric field; if the result of a conversion is wider than
the field width, the field is expanded to contain the conversion result.
RETURN VALUES
These functions return the number of characters printed (not including the trailing `\0' used to end output to strings), except for
snprintf() and vsnprintf(), which return the number of characters that would have been printed if the size were unlimited (again,
not including the final `\0'). These functions return a negative value if an error occurs.
EXAMPLES
To print a date and time in the form ``Sunday, July 3, 10:02'', where weekday and month are pointers to strings:
#include <stdio.h>
fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
To print pi to five decimal places:
#include <math.h>
#include <stdio.h>
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
To allocate a 128 byte string and print into it:
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
char *newfmt(const char *fmt, ...)
{
char *p;
va_list ap;
if ((p = malloc(128)) == NULL)
return (NULL);
va_start(ap, fmt);
(void) vsnprintf(p, 128, fmt, ap);
va_end(ap);
return (p);
}
COMPATIBILITY
The conversion formats %D, %O, and %U are not standard and are provided only for backward compatibility. The effect of padding the
%p format with zeros (either by the 0 flag or by specifying a precision), and the benign effect (i.e., none) of the # flag on %n and
%p conversions, as well as other nonsensical combinations such as %Ld, are not standard; such combinations should be avoided.
ERRORS
In addition to the errors documented for the write(2) system call, the printf() family of functions may fail if:
[EILSEQ] An invalid wide character code was encountered.
[ENOMEM] Insufficient storage space is available.
SEE ALSO
printf(1), printf_l(3), fmtcheck(3), scanf(3), setlocale(3), stdarg(3), wprintf(3)
STANDARDS
Subject to the caveats noted in the BUGS section below, the fprintf(), printf(), sprintf(), vprintf(), vfprintf(), and vsprintf()
functions conform to ANSI X3.159-1989 (``ANSI C89'') and ISO/IEC 9899:1999 (``ISO C99''). With the same reservation, the snprintf()
and vsnprintf() functions conform to ISO/IEC 9899:1999 (``ISO C99''), while dprintf() and vdprintf() conform to IEEE Std 1003.1-2008
(``POSIX.1'').
HISTORY
The functions asprintf() and vasprintf() first appeared in the GNU C library. These were implemented by Peter Wemm
<peter@FreeBSD.org> in FreeBSD 2.2, but were later replaced with a different implementation from OpenBSD 2.3 by Todd C. Miller
<Todd.Miller@courtesan.com>. The dprintf() and vdprintf() functions were added in FreeBSD 8.0.
BUGS
The printf family of functions do not correctly handle multibyte characters in the format argument.
SECURITY CONSIDERATIONS
The sprintf() and vsprintf() functions are easily misused in a manner which enables malicious users to arbitrarily change a running
program's functionality through a buffer overflow attack. Because sprintf() and vsprintf() assume an infinitely long string,
callers must be careful not to overflow the actual space; this is often hard to assure. For safety, programmers should use the
snprintf() interface instead. For example:
void
foo(const char *arbitrary_string, const char *and_another)
{
char onstack[8];
#ifdef BAD
/*
* This first sprintf is bad behavior. Do not use sprintf!
*/
sprintf(onstack, "%s, %s", arbitrary_string, and_another);
#else
/*
* The following two lines demonstrate better use of
* snprintf().
*/
snprintf(onstack, sizeof(onstack), "%s, %s", arbitrary_string,
and_another);
#endif
}
The printf() and sprintf() family of functions are also easily misused in a manner allowing malicious users to arbitrarily change a
running program's functionality by either causing the program to print potentially sensitive data ``left on the stack'', or causing
it to generate a memory fault or bus error by dereferencing an invalid pointer.
%n can be used to write arbitrary data to potentially carefully-selected addresses. Programmers are therefore strongly advised to
never pass untrusted strings as the format argument, as an attacker can put format specifiers in the string to mangle your stack,
leading to a possible security hole. This holds true even if the string was built using a function like snprintf(), as the result-
ing string may still contain user-supplied conversion specifiers for later interpolation by printf(). For this reason, a format
argument containing %n is assumed to be untrustworthy if located in writable memory (i.e. memory with protection PROT_WRITE; see
mprotect(2)) and any attempt to use such an argument is fatal. Practically, this means that %n is permitted in literal format
strings but disallowed in format strings located in normal stack- or heap-allocated memory.
Always use the proper secure idiom:
snprintf(buffer, sizeof(buffer), "%s", string);
BSD December 2, 2009 BSDSTDARG(3)
STDARG(3) BSD Library Functions Manual STDARG(3)
NAME
stdarg -- variable argument lists
SYNOPSIS
#include <stdarg.h>
void
va_start(va_list ap, last);
type
va_arg(va_list ap, type);
void
va_copy(va_list dest, va_list src);
void
va_end(va_list ap);
DESCRIPTION
A function may be called with a varying number of arguments of varying types. The include file <stdarg.h> declares a type (va_list)
and defines three macros for stepping through a list of arguments whose number and types are not known to the called function.
The called function must declare an object of type va_list which is used by the macros va_start(), va_arg(), va_copy(), and
va_end().
The va_start() macro must be called first, and it initializes ap, which can be passed to va_arg() for each argument to be processed.
Calling va_end() signals that there are no further arguments, and causes ap to be invalidated. Note that each call to va_start()
must be matched by a call to va_end(), from within the same function.
The parameter last is the name of the last parameter before the variable argument list, i.e., the last parameter of which the call-
ing function knows the type.
Because the address of this parameter is used in the va_start() macro, it should not be declared as a register variable, or as a
function or an array type.
The va_arg() macro expands to an expression that has the type and value of the next argument in the call. The parameter ap is the
va_list ap initialized by va_start(). Each call to va_arg() modifies ap so that the next call returns the next argument. The
parameter type is a type name specified so that the type of a pointer to an object that has the specified type can be obtained sim-
ply by adding a * to type.
If there is no next argument, or if type is not compatible with the type of the actual next argument (as promoted according to the
default argument promotions), random errors will occur.
The first use of the va_arg() macro after that of the va_start() macro returns the argument after last. Successive invocations
return the values of the remaining arguments.
The va_copy() macro copies the state of the variable argument list, src, previously initialized by va_start(), to the variable argu-
ment list, dest, which must not have been previously initialized by va_start(), without an intervening call to va_end(). The state
preserved in dest is equivalent to calling va_start() and va_arg() on dest in the same way as was used on src. The copied variable
argument list can subsequently be passed to va_arg(), and must finally be passed to va_end() when through with it.
After a variable argument list is invalidated by va_end(), it can be reinitialized with va_start() or made a copy of another vari-
able argument list with va_copy().
EXAMPLES
The function foo takes a string of format characters and prints out the argument associated with each format character based on the
type.
void foo(char *fmt, ...)
{
va_list ap, ap2;
int d;
char c, *s;
va_start(ap, fmt);
va_copy(ap2, ap);
while (*fmt)
switch(*fmt++) {
case 's': /* string */
s = va_arg(ap, char *);
printf("string %s\n", s);
break;
case 'd': /* int */
d = va_arg(ap, int);
printf("int %d\n", d);
break;
case 'c': /* char */
/* Note: char is promoted to int. */
c = va_arg(ap, int);
printf("char %c\n", c);
break;
}
va_end(ap);
...
/* use ap2 to iterate over the arguments again */
...
va_end(ap2);
}
COMPATIBILITY
These macros are not compatible with the historic macros they replace. A backward compatible version can be found in the include
file <varargs.h>.
STANDARDS
The va_start(), va_arg(), va_copy(), and va_end() macros conform to ISO/IEC 9899:1999 (``ISO C99'').
BUGS
Unlike the varargs macros, the stdarg macros do not permit programmers to code a function with no fixed arguments. This problem
generates work mainly when converting varargs code to stdarg code, but it also creates difficulties for variadic functions that wish
to pass all of their arguments on to a function that takes a va_list argument, such as vfprintf(3).
BSD October 25, 2002 BSD