GNU Info

(libc.info)Other Output Conversions

---

Next: Formatted Output Functions Prev: Floating-Point Conversions Up: Formatted Output

---

Enter node , (file) or (file)node

Other Output Conversions
------------------------

   This section describes miscellaneous conversions for `printf'.

   The `%c' conversion prints a single character.  In case there is no
`l' modifier the `int' argument is first converted to an `unsigned
char'.  Then, if used in a wide stream function, the character is
converted into the corresponding wide character.  The `-' flag can be
used to specify left-justification in the field, but no other flags are
defined, and no precision or type modifier can be given.  For example:

     printf ("%c%c%c%c%c", 'h', 'e', 'l', 'l', 'o');

prints `hello'.

   If there is a `l' modifier present the argument is expected to be of
type `wint_t'.  If used in a multibyte function the wide character is
converted into a multibyte character before being added to the output.
In this case more than one output byte can be produced.

   The `%s' conversion prints a string.  If no `l' modifier is present
the corresponding argument must be of type `char *' (or `const char
*').  If used in a wide stream function the string is first converted
in a wide character string.  A precision can be specified to indicate
the maximum number of characters to write; otherwise characters in the
string up to but not including the terminating null character are
written to the output stream.  The `-' flag can be used to specify
left-justification in the field, but no other flags or type modifiers
are defined for this conversion.  For example:

     printf ("%3s%-6s", "no", "where");

prints ` nowhere '.

   If there is a `l' modifier present the argument is expected to be of
type `wchar_t' (or `const wchar_t *').

   If you accidentally pass a null pointer as the argument for a `%s'
conversion, the GNU library prints it as `(null)'.  We think this is
more useful than crashing.  But it's not good practice to pass a null
argument intentionally.

   The `%m' conversion prints the string corresponding to the error
code in `errno'.  Note: Error Messages.  Thus:

     fprintf (stderr, "can't open `%s': %m\n", filename);

is equivalent to:

     fprintf (stderr, "can't open `%s': %s\n", filename, strerror (errno));

The `%m' conversion is a GNU C library extension.

   The `%p' conversion prints a pointer value.  The corresponding
argument must be of type `void *'.  In practice, you can use any type
of pointer.

   In the GNU system, non-null pointers are printed as unsigned
integers, as if a `%#x' conversion were used.  Null pointers print as
`(nil)'.  (Pointers might print differently in other systems.)

   For example:

     printf ("%p", "testing");

prints `0x' followed by a hexadecimal number--the address of the string
constant `"testing"'.  It does not print the word `testing'.

   You can supply the `-' flag with the `%p' conversion to specify
left-justification, but no other flags, precision, or type modifiers
are defined.

   The `%n' conversion is unlike any of the other output conversions.
It uses an argument which must be a pointer to an `int', but instead of
printing anything it stores the number of characters printed so far by
this call at that location.  The `h' and `l' type modifiers are
permitted to specify that the argument is of type `short int *' or
`long int *' instead of `int *', but no flags, field width, or
precision are permitted.

   For example,

     int nchar;
     printf ("%d %s%n\n", 3, "bears", &nchar);

prints:

     3 bears

and sets `nchar' to `7', because `3 bears' is seven characters.

   The `%%' conversion prints a literal `%' character.  This conversion
doesn't use an argument, and no flags, field width, precision, or type
modifiers are permitted.