MATLAB Functions

Write formatted data to file

count = fprintf(fid,format,A,...)
fprintf(format,A,...)

Description

count = fprintf(fid,format,A,...)

formats the data in the real part of matrix A (and in any additional matrix arguments) under control of the specified format string, and writes it to the file associated with file identifier fid. fprintf returns a count of the number of bytes written.

Argument fid is an integer file identifier obtained from fopen. (It may also be 1 for standard output (the screen) or 2 for standard error. See fopen for more information.) Omitting fid from fprintf's argument list causes output to appear on the screen, and is the same as writing to standard output (fid = 1)

fprintf(format,A,...)

writes to standard output--the screen.

The format string specifies notation, alignment, significant digits, field width, and other aspects of output format. It can contain ordinary alphanumeric characters; along with escape characters, conversion specifiers, and other characters, organized as shown below:

For more information see "Tables" and "References".

Remarks

The fprintf function behaves like its ANSI C language fprintf() namesake with certain exceptions and extensions. These include:

The following non-standard subtype specifiers are supported for conversion specifiers %o, %u, %x, and %X.

t
The underlying C data type is a float rather than an unsigned integer.

b
The underlying C data type is a double rather than an unsigned integer.

For example, to print a double-precision value in hexadecimal, use a format like '%bx'.
The fprintf function is vectorized for the case when input matrix A is nonscalar. The format string is cycled through the elements of A (columnwise) until all the elements are used up. It is then cycled in a similar manner, without reinitializing, through any additional matrix arguments.

`t`	The underlying C data type is a float rather than an unsigned integer.
`b`	The underlying C data type is a double rather than an unsigned integer.

Tables

The following tables describe the non-alphanumeric characters found in format specification strings.

Escape Characters

Character Description
\n
New line

\t
Horizontal tab

\b
Backspace

\r
Carriage return

\f
Form feed

\\
Backslash

\'' or ''

Single quotation mark

%%
Percent character

`Character`	`Description`
`\n`	New line
`\t`	Horizontal tab
`\b`	Backspace
`\r`	Carriage return
`\f`	Form feed
`\\`	Backslash
\'' or ''	Single quotation mark
`%%`	Percent character

Conversion characters specify the notation of the output.

Conversion Specifiers

Specifier Description
%c
Single character

%d
Decimal notation (signed)

%e
Exponential notation (using a lowercase e as in 3.1415e+00)

%E
Exponential notation (using an uppercase E as in 3.1415E+00)

%f
Fixed-point notation

%g
The more compact of %e or %f, as defined in [2]. Insignificant zeros do not print.

%G
Same as %g, but using an uppercase E

%o
Octal notation (unsigned)

%s
String of characters

%u
Decimal notation (unsigned)

%x
Hexadecimal notation (using lowercase letters a-f)

%X
Hexadecimal notation (using uppercase letters A-F)

`Specifier`	`Description`
`%c`	Single character
`%d`	Decimal notation (signed)
`%e`	Exponential notation (using a lowercase `e` as in `3.1415e+00`)
`%E`	Exponential notation (using an uppercase `E` as in `3.1415E+00`)
`%f`	Fixed-point notation
`%g`	The more compact of `%e` or `%f`, as defined in [2]. Insignificant zeros do not print.
`%G`	Same as `%g`, but using an uppercase `E`
`%o`	Octal notation (unsigned)
`%s`	String of characters
`%u`	Decimal notation (unsigned)
`%x`	Hexadecimal notation (using lowercase letters `a`-`f`)
`%X`	Hexadecimal notation (using uppercase letters `A`-`F`)

Other characters can be inserted into the conversion specifier between the % and the conversion character.

Other Characters

Character Description Example
A minus sign (-)
Left-justifies the converted argument in its field.
%-5.2d

A plus sign (+)
Always prints a sign character (+ or -).
%+5.2d

Zero (0)
Pad with zeros rather than spaces.
%05.2d

Digits (field width)
A digit string specifying the minimum number of digits to be printed.
%6f

Digits (precision)
A digit string including a period (.) specifying the number of digits to be printed to the right of the decimal point.
%6.2f

`Character`	`Description`	`Example`
A minus sign (`-`)	Left-justifies the converted argument in its field.	`%-5.2d`
A plus sign (`+`)	Always prints a sign character (+ or -).	`%+5.2d`
Zero (`0`)	Pad with zeros rather than spaces.	`%05.2d`
Digits (field width)	A digit string specifying the minimum number of digits to be printed.	`%6f`
Digits (precision)	A digit string including a period (.) specifying the number of digits to be printed to the right of the decimal point.	`%6.2f`

For more information about format strings, refer to the printf() and fprintf() routines in the documents listed in "References".

Examples

The statements

x = 0:.1:1;
y = [x; exp(x)];
fid = fopen('exp.txt','w');
fprintf(fid,'%6.2f %12.8f\n',y);
fclose(fid)

create a text file called exp.txt containing a short table of the exponential function:

0.00    1.00000000
0.10    1.10517092
...
1.00    2.71828183

The command

fprintf('A unit circle has circumference %g.\n',2*pi)

displays a line on the screen:

A unit circle has circumference 6.283186.

To insert a single quotation mark in a string, use two single quotation marks together. For example,

fprint(1,'It''s Friday.\n')

displays on the screen:

It's Friday.

The commands

B = [8.8  7.7; 8800  7700]
fprintf(1,'X is %6.2f meters or %8.3f mm\n',9.9,9900,B)

display the lines:

X is 9.90 meters or 9900.000 mm
X is 8.80 meters or 8800.000 mm
X is 7.70 meters or 7700.000 mm

Explicitly convert MATLAB double-precision variables to integral values for use with an integral conversion specifier. For instance, to convert signed 32-bit data to hexadecimal format:

a = [6 10 14 44];
fprintf('%9X\n',a + (a<0)*2^32)
        6
        A
        E
       2C