printf(), fprintf(), sprintf(), snprintf(), vprintf(), vfprintf(), vsprintf(), vsnprintf() - formatted output conversion
#include <stdio.h>
int printf (const char *format ...)
int fprintf (FILE *stream, const char *format ...)
int sprintf (char *str, const char *format ...)
int snprintf (char *str, size_t size, const char *format ...)
#include <stdarg.h>
int vprintf (const char *format, va_list ap)
int vfprintf (FILE *stream, const char *format, va_list ap)
int vsprintf (char *str, const char *format, va_list ap)
int vsnprintf (char *str, size_t size, const char *format, va_list ap)
The functions in the printf(3) family produce output according to a format, as described below. Printf(3) and vprintf(3) write output to stdout, the standard output stream; fprintf(3) and vfprintf(3) write output to the specified output stream; sprintf(3), snprintf(3), vsprintf(3), and vsnprintf(3) write to the character string str.
These functions return the number of characters printed (not
including the trailing \0 used to end output to
strings). Sprintf(3) and vsprintf(3) effectively assume
an infinite size.
Snprintf(3) and vsnprintf(3) write at most size-1 of the characters printed into the output string (the size'th character then get the terminating \0); if the return value is greater than or equal to the size, the string was too short and some of the printed characters were discarded. Sprintf(3) and vsprintf(3) effectively assume an infinite size.
The output is written according to the format string that specifies how subsequent arguments (or arguments accessed through the variable-length argument facilities of <stdarg.h>) are converted for output.
The format string contains zero or more directives; a directive
is either an ordinary character (any character but %),
which is copied unchanged to the output stream. The format string
is composed of zero or more directives: ordinary characters (not
%), which are copied unchanged to the output stream;
or a conversion specification. A conversion specification fetches
zero or more subsequent arguments. Each conversion specification is
introduced by the character %. The arguments must
correspond properly (after type promotion) with the conversion
specifier. The syntax of a conversion specifier is:
%[#][0][-][ ][+][width][.[precision]][h|l|L|q]type
Only the type is required.
In sequence, these flags are:
# character specifies that the value should be
converted to an "alternate form". This affects only o,
x, X, e, E,
f, g, and G conversions.
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).x and X conversions, a non-zero
result has the string 0x (or 0X for
X conversions) prepended to it.e, E, f,
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).g and G conversions, the result
will always contain a decimal point, even if no digits follow it,
and trailing zeros are not removed from the result as they would
otherwise be.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.- 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.(d
e, E, f, g,
G, or i).+ character specifies that a sign always be
placed before a number produced by a signed conversion. A
+ overrides a space if both are used.A field width may be indicated by an asterisk *
instead of a digit string. In this case, an int argument
supplies the field width. A negative field width is treated as a
left adjustment flag followed by a positive field width.
.
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 e, E, 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.
A precision may be indicated by an asterisk *
instead of a digit string. In this case, an int argument
supplies the precision. A negative precision is treated as though
it were missing.
h|l|L|qh, l
(ell), L, or q, depending on the
conversion type The values are:
d, i, o,
u, x, or X conversion
corresponds to a short int or unsigned short int
argument, or that a following n conversion corresponds
to a pointer to a short int argument.d, i,
o, u, x, or X
conversion applies to a pointer to a long int or unsigned
long int argument, or that a following n conversion corresponds
to a pointer to a long int argument.e, E, f,
g, or G conversion corresponds to a
long double argument.d, i, o,
u, x, or X conversion
applies to a pointer to a quad_t or u_quad_t
(unsigned long int) argument, or that a following n
conversion corresponds to a pointer to a quad_t argument.
The types quad_t (extended precisions) and u_quad_t
(unsigned extended precision) are defined in
<sys/types.h>. Two l (ell) conversion option
characters are equivalent to a single q.| Type | Argument | Conversion |
|---|---|---|
| % | Prints literal % character | |
| c | int | Prints a character |
| d | int | Signed decimal |
| D | long int | Signed decimal; equivalent to ld |
| e | double | Decimal in form
[-]d.ddde[mdd] |
| E | double | Decimal in form
[-]d.dddE[mdd] |
| f | double | Decimal in form
[-]ddd.ddd |
| g | double | The more compact of f or e format |
| i | int | Signed decimal |
| n | int * | Number of character printed so far stored in argument |
| o | int | Unsigned octal |
| O | long int | Unsigned octal; equivalent to lo |
| p | void * | Hexadecimal value of pointer, as for %#x or %#lx |
| s | char * | String |
| u | int | Unsigned decimal |
| U | long int | Unsigned decimal; equivalent to lu |
| X | int | Unsigned hexadecimal using letters ABCDEF |
| x | int | Unsigned hexadecimal using letters abcdef |
Note:
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.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 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.% is written. No argument is converted. The
complete conversion specification is %%.In no case does a nonexistent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.
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 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 *nefmt(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);
}
printf(1)
scanf(3)
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