int fprintf ( FILE * stream, const char * format, ... );
Write formatted data to stream
Writes the C string pointed by format to the stream. If format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers.

After the format parameter, the function expects at least as many additional arguments as specified by format.


Pointer to a FILE object that identifies an output stream.
C string that contains the text to be written to the stream.
It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested.

A format specifier follows this prototype:


Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument:
d or iSigned decimal integer392
uUnsigned decimal integer7235
oUnsigned octal610
xUnsigned hexadecimal integer7fa
XUnsigned hexadecimal integer (uppercase)7FA
fDecimal floating point, lowercase392.65
FDecimal floating point, uppercase392.65
eScientific notation (mantissa/exponent), lowercase3.9265e+2
EScientific notation (mantissa/exponent), uppercase3.9265E+2
gUse the shortest representation: %e or %f392.65
GUse the shortest representation: %E or %F392.65
aHexadecimal floating point, lowercase-0xc.90fep-2
AHexadecimal floating point, uppercase-0XC.90FEP-2
sString of characterssample
pPointer addressb8000000
nNothing printed.
The corresponding argument must be a pointer to a signed int.
The number of characters written so far is stored in the pointed location.
%A % followed by another % character will write a single % to the stream.%

The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are optional and follow these specifications:

-Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space)If no sign is going to be written, a blank space is inserted before the value.
#Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero.
Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).

(number)Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
*The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.

.numberFor integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0.
For a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6).
For g and G specifiers: This is the maximum number of significant digits to be printed.
For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered.
If the period is specified without an explicit value for precision, 0 is assumed.
.*The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.

The length sub-specifier modifies the length of the data type. This is a chart showing the types used to interpret the corresponding arguments with and without length specifier (if a different type is used, the proper type promotion or conversion is performed, if allowed):
lengthd iu o x Xf F e E g G a Acspn
(none)intunsigned intdoubleintchar*void*int*
hhsigned charunsigned charsigned char*
hshort intunsigned short intshort int*
llong intunsigned long intwint_twchar_t*long int*
lllong long intunsigned long long intlong long int*
Llong double
Note that the c specifier takes an int (or wint_t) as argument, but performs the proper conversion to a char value (or a wchar_t) before formatting it for output.

Note: Yellow rows indicate specifiers and sub-specifiers introduced by C99. See <cinttypes> for the specifiers for extended types.
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n).
There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function.

Return Value

On success, the total number of characters written is returned.

If a writing error occurs, the error indicator (ferror) is set and a negative number is returned.

If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.


/* fprintf example */
#include <stdio.h>

int main ()
   FILE * pFile;
   int n;
   char name [100];

   pFile = fopen ("myfile.txt","w");
   for (n=0 ; n<3 ; n++)
     puts ("please, enter a name: ");
     gets (name);
     fprintf (pFile, "Name %d [%-10.10s]\n",n+1,name);
   fclose (pFile);

   return 0;

This example prompts 3 times the user for a name and then writes them to myfile.txt each one in a line with a fixed length (a total of 19 characters + newline).
Two format tags are used:
%d : Signed decimal integer
%-10.10s : left-justified (-), minimum of ten characters (10), maximum of ten characters (.10), string (s).
Assuming that we have entered John, Jean-Francois and Yoko as the 3 names, myfile.txt would contain:

Name 1 [John      ] 
Name 2 [Jean-Franc] 
Name 3 [Yoko      ]

For more examples on formatting see printf.


Particular library implementations may support additional specifiers and sub-specifiers.
Those listed here are supported by the latest C and C++ standards (both published in 2011), but those in yellow were introduced in C99 (only required for C++ implementations since C++11), and may not be supported by libraries that comply with older standards.

See also