printf(3) Library Functions Manual printf(3)
NAME
printf, fprintf, snprintf, sprintf - Print formatted output
LIBRARY
Standard C Library (libc.so, libc.a)
SYNOPSIS
#include <stdio.h>
int printf(
const char *format [,value]...);
int fprintf(
FILE *stream,
const char *format [,value]...);
int snprintf(
char *string, size_t n,
const char *format [,value]...);
int sprintf(
char *string,
const char *format [,value]...);
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
fprintf(), printf(), snprintf(), sprintf(): ISO C, XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies a character string combining literal characters with conversion specifications. Specifies the data to be converted according to
the format parameter. Points to a FILE structure specifying an open stream to which converted values will be written. Points to a charac-
ter array in which the converted values will be stored. Specifies the size of the buffer referred to by string.
DESCRIPTION
The format parameter is a character string that contains two types of objects: Literal characters, which are copied to the output stream.
Conversion specifications, each of which causes zero or more items to be fetched from the value parameter list.
If the value parameter list does not contain enough items to process all of the conversion specifications in the format parameter, the
results are unpredictable. If more value items remain after the entire format has been processed, they are ignored.
Function descriptions: Converts, formats, and writes its value parameters, under control of the format parameter, to the standard output
stream stdout. Converts, formats, and writes its value parameters, under control of the format parameter, to the output stream specified
by the stream parameter. Converts, formats, and stores its value parameters, under control of the format parameter, into consecutive bytes
starting at the address specified by the string parameter. The sprintf() function places a null character ( ) at the end. You must ensure
that enough storage space is available to contain the formatted string. Identical to sprintf() with the addition of the n argument, which
states the size of the buffer referred to by string.
Conversion Specifications
Each conversion specification in the format parameter has the following syntax: A % (percent sign).
The printf() functions can handle a format string that enables the system to process elements of the parameter list in variable
order. In such a case, the normal conversion character % (percent sign) is replaced by %digit$, where digit is a decimal number in
the range from 1 to NL_ARGMAX. Conversion is then applied to the specified argument instead of the next unused argument. This fea-
ture provides for the definition of format strings in an order appropriate to specific languages. When variable ordering is used,
the * (asterisk) specification for field width or precision is replaced by *digit$. If the variable ordering feature is used, it
must be specified for all conversions. Zero or more flags that modify the meaning of the conversion specification. The flag charac-
ters and their meanings are as follows: Format the integer portion of a decimal conversion (%i, %d, %u, %f, %g, %G) with the thou-
sands grouping character. The thousands grouping character used in the result is the one specified by the current locale for numeric
values, not the one specified for monetary values. The result of using the ' flag with conversions other than decimal is undefined.
Left align within the field the result of the conversion. If you do not specify this flag, the converted value is right aligned
within the field. Begin the result of a signed conversion with a sign (+ or -). If you do not specify this flag, the converted
value begins with a sign only when the value is negative. Prefix a space character to the result if the first character of a signed
conversion is not a sign or if a signed conversion results in no characters. If both the (space) and + flags appear, the (space)
flag is ignored. Convert the value to an alternative form. For o conversion, the function increases the precision to force the
first digit of the result to be a 0 (zero). For x and X conversions, a nonzero result has 0x or 0X prefixed to it. For e, E, f, g,
and G conversions, the result always contains a radix character, even if no digits follow it. For g and G conversions, trailing
zeros are not removed from the result. For c, C, d, i, s, S, and u conversions, the flag has no effect. Pad to field width using
leading zeros (following any indication of sign or base) for d, i, o, u, x, X, e, E, f, g, and G conversions; no space padding is
performed. If the 0 and - (dash) flags both appear, the 0 flag is ignored. The 0 flag is also ignored if a precision is specified
for d, i, o u, x, and X conversions. For other conversions, the behavior is undefined. An optional decimal digit string that spec-
ifies the minimum field width. If the converted value has fewer characters than the field width, the field is padded on the left to
the length specified by the field width. If the left-adjustment flag is specified, the field is padded on the right.
A field width can be indicated by an * (asterisk) instead of a digit string. In this case, an integer (int) *Vvalue parameter sup-
plies the field width. The value parameter converted for output is not fetched until the conversion letter is reached, so the
parameters specifying field width or precision must appear before the value (if any) to be converted. If the corresponding parame-
ter has a negative value, it is treated as a - left-alignment option followed by a positive field width. When variable ordering
with the %digit$ format is used, the * (asterisk) specification for field width or precision is replaced by *digit$. An optional
precision. The precision is a . (dot) followed by a decimal digit string. If no precision is given, the decimal digit string is
treated as 0 (zero). The precision specifies: The minimum number of digits to appear for the d, u, o, x, and X conversions. The
number of digits to appear after the radix character for the e, E, and f conversions. The maximum number of significant digits for
the g and G conversions. The maximum number of bytes to be printed from a string in the s and S conversions.
A field precision can be indicated by an * (asterisk) instead of a digit string. In this case, an integer (int) value parameter sup-
plies the field precision. The value parameter converted for output is not fetched until the conversion letter is reached, so the
parameters specifying field width or precision must appear before the value (if any) to be converted. If the value of the corre-
sponding parameter is negative, the value is treated as if the precision was not specified. When variable ordering with the %digit$
format is used, the * (asterisk) specification for field width or precision is replaced by *digit$. An optional h or l indicating
the size of the argument corresponding to the following integer or floating-point conversion specifier. An h followed by a d, i, o,
u, x, or X conversion specifier indicates that the argument will be treated as a short int or unsigned short int. An h followed by
an n indicates that the argument will be treated as a pointer to a short int. An l followed by a d, i, o, u, x, or X conversion
specifier indicates that the argument will be treated as a long int or unsigned long int. An l followed by an n indicates that the
argument will be treated as a pointer to a long int.
[ISO C] An l followed by a c conversion specifier applies to a wint_t argument. An l followed by an s conversion specifier applies
to a pointer to a wchar_t argument. An optional L indicating that the argument corresponding to the floating-point conversion spec-
ifier will be treated as a long double. One of the following characters that indicate the type of conversion to be applied: Accepts
a value of type int and converts it to signed decimal notation. The precision specifies the minimum number of digits to appear. If
the value being converted can be represented in fewer digits, it is expanded with leading zeros. The default precision is 1. The
result of converting a 0 (zero) value with a precision of 0 (zero) is a null string. Specifying a field width with a 0 (zero) as the
leading character causes the field width value to be padded with leading zeros. Accepts a value of type int and converts it to
unsigned decimal notation. The precision specifies the minimum number of digits to appear. If the value being converted can be rep-
resented in fewer digits, it is expanded with leading zeros. The default precision is 1. The result of converting a 0 (zero) value
with a precision of 0 (zero) is a null string. Specifying a field width with a 0 (zero) as the leading character causes the field
width value to be padded with leading zeros. Accepts a value of type int and converts it to unsigned octal notation. The precision
specifies the minimum number of digits to appear. If the value being converted can be represented in fewer digits, it is expanded
with leading zeros. The default precision is 1. The result of converting a 0 (zero) value with a precision of 0 (zero) is a null
string. Specifying a field width with a 0 (zero) as the leading character causes the field width value to be padded with leading
zeros. An octal value for field width is not implied. Accepts a value of type int and converts it to unsigned hexadecimal notation.
The letters abcdef are used for the x conversion and the letters ABCDEF are used for the X conversion. The precision specifies the
minimum number digits to appear. If the value being converted can be represented in fewer digits, it is expanded with leading zeros.
The default precision is 1. The result of converting a 0 (zero) value with a precision of 0 (zero) is a null string. Specifying a
field width with a 0 (zero) as the leading character causes the field width value to be padded with leading zeros. Accepts a value
of type float, double, or long double and converts it to decimal notation in the format [-]ddd.ddd. The number of digits after the
radix character is equal to the precision specification. If no precision is specified, six digits are output. If the precision is 0
(zero), no radix character appears (unless the # flag is specified). If a radix character is output, at least one digit is output
before it. The value is rounded to the appropriate number of digits. Accepts a value of type float, double, or long double and
converts it to the exponential form [-]d.ddde+/-dd. There is one digit before the radix character and the number of digits after
the radix character is equal to the precision specification. If no precision is specified, six digits are output. If the precision
is 0 (zero), no radix character appears (unless the # flag is specified). The E conversion character produces a number with E
instead of e before the exponent. The exponent always contains at least two digits. If the value is 0 (zero), the exponent is 0
(zero). Accepts a value of type float, double, or long double and converts it in the style of the e, E, or f conversion characters,
with the precision specifying the number of significant digits. If an explicit precision is zero, it is ignored (treated as 1).
Trailing zeros are removed from the result. A radix character appears only if it is followed by a digit (except the case in which
the radix character always appears if the # flag is specified). The style used depends on the value converted. Style e (E, if the G
flag is used) results only if the exponent resulting from the conversion is less than -4 or if the exponent is greater than or equal
to the precision. If the l qualifier is not present, accepts a value of type int, converts it to an unsigned char, and prints it.
[ISO C] If the l qualifier is present, treats the c argument as wint_t, converts it to a two-element wchar_t array (the first ele-
ment being the wint_t argument and the second being a null wide-character), and prints the converted value. Accepts a value of type
wchar_t, converts it to an array of bytes containing a multibyte character, and prints the character. If a minimum field width is
specified and the multibyte character occupies fewer bytes than the specified width, the multibyte character is padded with space
characters to the specified width. If the l qualifier is not present, accepts a pointer to an array of type char. Bytes from the
array are printed until a null character is encountered or the number of characters indicated by the precision is reached. If no
precision is specified, all characters up to the first null character are printed. If the precision is not specified or is greater
than the size of the array, the array must be terminated by a null byte. If the string pointer value has a value of 0 (zero) or
null, the results are undefined.
[ISO C] If the l qualifier is present, the s argument is treated as a pointer to an array of type wchar_t. Wide-characters from
the array are converted to multibyte characters. Conversion of each wide-character is done as if by a call to the wcrtomb() func-
tion (with the conversion state described by a mbstate_t object initialized to zero before the first wide-character is converted) up
to, but not including, the terminating null wide-character. The resulting bytes (including shift sequences) are written up to, but
not including, the terminating null byte. If no precision is specified, the wide-character array contains a null wide-character. If,
for a specified precision, the function would need to access one wide-character past the end of the array to equal the length of a
complete multibyte character sequence, the array also contains a null wide-character; in other words, the function does not output a
partial multibyte character sequence. Accepts a pointer to an array of type wchar_t. Wide-characters from the array are converted
to an array of bytes containing multibyte characters and the multibyte characters up to, but not including, the null character are
printed. If a precision is specified, no more than the number of bytes specified by the precision are printed. If the precision is
not specified or is greater than the size of the array of bytes, the array of wide-characters must be terminated by a null wide-
character. If a minimum field width is specified and the array of bytes occupy fewer bytes than the specified width, the array is
padded with space characters to the specified width. Accepts a pointer to void. The value of the pointer is converted to a sequence
of printable characters, the same as unsigned long hexadecimal (lx). Accepts a pointer to an integer into which is written the num-
ber of characters written to the output stream so far by this call. No argument is converted. Prints a % wide-character. No argu-
ment is converted. The complete conversion specification is %%.
If a conversion specification is invalid, results are undefined.
If any argument is, or points to, a union or an aggregate (except for an array of type char using %s conversion, an array of type wchar_t
using %s conversion, or a pointer using %p conversion), the function's behavior is undefined.
If the result of a conversion is wider than the field width, the field is expanded to contain the converted result. No truncation occurs.
However, a small precision can cause truncation on the right.
The e, E, f, and g formats represent the special floating-point values as follows: +NaNQ or -NaNQ +NaNS or -NaNS +INF or -INF +0 or -0
The representation of the + (plus sign) depends on whether the + or (space) formatting flag is specified.
All forms of the printf() functions allow for the insertion of a language-dependent radix character in the output string. The radix char-
acter is defined by langinfo data in the program's locale (category LC_NUMERIC). In the POSIX (C) locale or in a locale where the radix
character is not defined, the radix character defaults to a period (.).
The st_ctime and st_mtime fields of the file are marked for update between the successful execution of the printf() or fprintf() function
and the next successful completion of a call to one of the following: The fflush() or fclose() function on the same stream The exit() or
abort() function
RESTRICTIONS
Currently, the Tru64 UNIX product does not include locales that use shift-state encoding. Some sections of this reference page refer to the
mb_state object or describe behavior that is dependent on shift-state encoding. This information is included for your convenience in devel-
oping portable applications that run on multiple platforms, some of which may supply locales that do use shift-state encoding.
RETURN VALUES
Upon successful completion, each of these functions returns the number of bytes in the output string. Otherwise, a negative value is
returned.
The value returned by the snprintf() or sprintf() function does not include the final null character ( ).
ERRORS
The printf() or fprintf() functions fail if either stream is unbuffered or stream's buffer needed to be flushed and the function call
caused an underlying write() or lseek() function to be invoked. In addition, if the printf() or fprintf() function fails, errno is set to
one of the following values: The O_NONBLOCK flag is set for the file descriptor underlying stream and the process would be delayed in the
write operation. The file descriptor underlying stream is not a valid file descriptor open for writing. An attempt was made to write to a
file that exceeds the process's file size limit or the maximum file size. An invalid wide-character was detected. The read operation was
interrupted by a signal that was caught, and no data was transferred. The implementation supports job control; the process is a member of
a background process group and is attempting to write to its controlling terminal; TOSTOP is set; the process is neither ignoring nor
blocking SIGTTOU; and the process group of the process is orphaned. This error may also be returned under implementation-defined condi-
tions. No free space remained on the device containing the file. An attempt was made to write to a pipe or FIFO that is not open for
reading by any process. A SIGPIPE signal will also be sent to the process.
RELATED INFORMATION
Functions: conv(3), ecvt(3), putc(3), scanf(3), vprintf(3), vwprintf(3), wprintf(3), wscanf(3) delim off
printf(3)