PRINTF(3) | Library Functions Manual | PRINTF(3) |

`\0`

’); if the
return value is greater than or equal to the
`\0`

’ byte, or -1 on
error, will be returned.
- 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**. - Zero or more of the following flags:
- A hash ‘
**#**’ character specifying that the value should be converted to an “alternate form”. For**o**conversions, the precision of the number is increased to force the first character of the output string to a zero (except if a zero value is printed with an explicit precision of 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 follows). For**g**and**G**conversions, trailing zeros are not removed from the result as they would otherwise be. For all other formats, behaviour is undefined. - A zero ‘
**0**’ character specifying 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**,**x**, and**X**), the ‘**0**’ flag is ignored. - A negative field width flag
‘
**-**’ indicates the converted value is to be left adjusted on the field boundary. Except for**n**conversions, 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. - A space, specifying that a blank should be left before
a positive number produced by a signed conversion
(
**d**,**a**,**A**,**e**,**E**,**f**,**F**,**g**,**G**, or**i**). - A ‘
**+**’ character specifying that a sign always be placed before a number produced by a signed conversion. A ‘**+**’ overrides a space if both are used.

- A hash ‘
- 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.
- An optional precision, in the form of a period
‘
**.**’ followed by an optional digit string. If the digit string is omitted, the precision 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. - 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 * **t**modifier, when applied to an**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****e, E, f, F, g, G**l (ell) double (ignored: same behavior as without it) L long double **c**or**s**conversion:**Modifier****c****s**l (ell) wint_t wchar_t * - A character that specifies the type of conversion to be applied.

`*`

’ 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**.**ddd**e**±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. If the argument is infinity, it will be converted to [-]inf (**e**) or [-]INF (**E**), respectively. If the argument is not-a-number (NaN), it will be converted to [-]nan (**e**) or [-]NAN (**E**), respectively. **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. If the argument is infinity, it will be converted to [-]inf (**f**) or [-]INF (**F**), respectively. If the argument is not-a-number (NaN), it will be converted to [-]nan (**f**) or [-]NAN (**F**), respectively. **gG**- The
`double`

argument is converted in style**f**or**e**(or**E**for**G**conversions). The precision specifies the number of significant 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. If the argument is infinity, it will be converted to [-]inf (**g**) or [-]INF (**G**), respectively. If the argument is not-a-number (NaN), it will be converted to [-]nan (**g**) or [-]NAN (**G**), respectively. **aA**- The
`double`

argument is rounded and converted to hexadecimal notation in the style [-]0xh**.**hhh**p**[±]d where the number of digits 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 followed 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,`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 represented with a mantissa of 0 (preceded by a ‘`-`

’ if appropriate) and an exponent of`+0`

. If the argument is infinity, it will be converted to [-]inf (**a**) or [-]INF (**A**), respectively. If the argument is not-a-number (NaN), it will be converted to [-]nan (**a**) or [-]NAN (**A**), respectively. **c**- The
`int`

argument is converted to an`unsigned char`

, and the resulting character is written. **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 number specified are written. If a precision is given, no NUL 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. **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. **%**- A ‘
`%`

’ is written. No argument is converted. The complete conversion specification is ‘`%%`

’.

`\0`

’ used to end output to strings).
The `\0`

’.).
The `\0`

’). A pointer to the newly allocated
string is returned in #include <stdio.h> fprintf(stdout, "%s, %s %d, %.2d:%.2d\n", weekday, month, day, hour, min);

#include <math.h> #include <stdio.h> fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));

#include <stdarg.h> #include <stdio.h> #include <stdlib.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); }

- [
`EILSEQ`

] - An invalid wide character code was encountered.
- [
`ENOMEM`

] - Insufficient storage space is available.
- [
`EOVERFLOW`

] - The return value would be too large to be represented by an
`int`.

`%s`

’. An attacker can put
format specifiers in the string to mangle the stack, leading to a possible
security hole. This holds true even if the string has been built “by
hand” using a function like int ret = snprintf(buffer, sizeof(buffer), "%s", string); if (ret == -1 || ret >= sizeof(buffer)) goto toolong;

June 12, 2017 | OpenBSD 6.1 |