Write data to text file - MATLAB fprintf
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fprintf
Write data to text file
Syntax
fprintf(fileID,formatSpec,A1,...,An)
fprintf(formatSpec,A1,...,An)
example
nbytes = fprintf( ___ )
example
example
Description
fprintf(fileID,formatSpec,A1,...,An) applies the formatSpec to all elements of arrays A1,...An in column order,
and writes the data to a text file. fprintf uses the encoding scheme specified in the call to fopen.
example
fprintf(formatSpec,A1,...,An) formats data and displays the results on the screen.
example
nbytes = fprintf( ___ ) returns the number of bytes that fprintf writes, using any of the input arguments in the
preceding syntaxes.
example
Examples
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Print Literal Text and Array Values
Print multiple numeric values and literal text to the screen.
A1 = [9.9, 9900];
A2 = [8.8, 7.7 ; ...
8800, 7700];
formatSpec = 'X is %4.2f meters or %8.3f mm\n';
fprintf(formatSpec,A1,A2)
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
%4.2f in the formatSpec input specifies that the first value in each line of output is a floating-point number with a field width of four digits,
including two digits after the decimal point. %8.3f in the formatSpec input specifies that the second value in each line of output is a floating-point
number with a field width of eight digits, including three digits after the decimal point. \n is a control character that starts a new line.
Print Double-Precision Values as Integers
Explicitly convert double-precision values with fractions to integer values.
a = [1.02, 3.04, 5.06];
fprintf('%d\n',round(a));
1
3
5
%d in the formatSpec input prints each value in the vector, round(a), as a signed integer. \n is a control character that starts a new line.
Write Table to Text File
Write a short table of the exponential function to a text file called exp.txt.
x = 0:.1:1;
A = [x; exp(x)];
fileID = fopen('exp.txt','w');
fprintf(fileID,'%6s %12s\n','x','exp(x)');
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Write data to text file - MATLAB fprintf
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fprintf(fileID,'%6.2f %12.8f\n',A);
fclose(fileID);
The first call to fprintf prints header text x and exp(x), and the second call prints the values from variable A.
If you plan to read the file with Microsoft® Notepad, use '\r\n' instead of '\n' to move to a new line. For example, replace the calls to fprintf
with the following:
fprintf(fileID,'%6s %12s\r\n','x','exp(x)');
fprintf(fileID,'%6.2f %12.8f\r\n',A);
MATLAB® import functions, all UNIX® applications, and Microsoft Word and WordPad recognize '\n' as a newline indicator.
View the contents of the file with the type command.
type exp.txt
x
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
exp(x)
1.00000000
1.10517092
1.22140276
1.34985881
1.49182470
1.64872127
1.82211880
2.01375271
2.22554093
2.45960311
2.71828183
Get Number of Bytes Written to File
Write data to a file and return the number of bytes written.
Write an array of data, A, to a file and get the number of bytes that fprintf writes.
A = magic(4);
fileID = fopen('myfile.txt','w');
nbytes = fprintf(fileID,'%5d %5d %5d %5d\n',A)
nbytes =
96
The fprintf function wrote 96 bytes to the file.
Close the file.
fclose(fileID);
View the contents of the file with the type command.
type('myfile.txt')
16
2
3
13
5
11
10
8
9
7
6
12
4
14
15
1
Display Hyperlinks in Command Window
Display a hyperlink (The MathWorks Web Site) on the screen.
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Write data to text file - MATLAB fprintf
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site = 'http://www.mathworks.com';
title = 'The MathWorks Web Site';
fprintf('<a href = "%s">%s</a>\n',site,title)
%s in the formatSpec input indicates that the values of the variables site and title, should be printed as strings.
■ Exporting a Cell Array to a Text File
■ Appending or Overwriting Existing Files
Input Arguments
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fileID — File identifier
1 (default) | 2 | scalar
File identifier, specified as one of the following:
■ A file identifier obtained from fopen.
■ 1 for standard output (the screen).
■ 2 for standard error.
Data Types: double
formatSpec — Format of the output fields
string
Format of the output fields, specified as a string.
The string can include a percent sign followed by a conversion character. The following table lists the available conversion characters and
subtypes.
Value Type
Conversion
Details
Integer, signed
%d or %i
Base 10
Integer, unsigned
%u
Base 10
%o
Base 8 (octal)
%x
Base 16 (hexadecimal), lowercase letters a–f
%X
Same as %x, uppercase letters A–F
%f
Fixed-point notation
%e
Exponential notation, such as 3.141593e+00
%E
Same as %e, but uppercase, such as 3.141593E+00
%g
The more compact of %e or %f, with no trailing zeros
%G
The more compact of %E or %f, with no trailing zeros
%bx or %bX
Double-precision hexadecimal, octal, or decimal value
Example: %bx prints pi as 400921fb54442d18
Floating-point number
%bo
%bu
%tx or %tX
%to
Single-precision hexadecimal, octal, or decimal value
Example: %tx prints pi as 40490fdb
%tu
Characters
%c
Single character
%s
String of characters
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The string can include optional operators, which appear in the following order (includes spaces for clarity):
Optional operators include:
■ Identifier
Order for processing inputs. Use the syntax n$, where n represents the position of the value in the input list.
For example, '%3$s %2$s %1$s %2$s' prints inputs 'A', 'B', 'C' as follows: C B A B.
■ Flags
'–'
Left-justify. Example: %-5.2f
'+'
Print sign character (+) for positive values. Example: %+5.2f
' '
Pad to field width with spaces before the value. Example: % 5.2f
'0'
Pad to field width with zeros. Example: %05.2f
'#'
Modify selected numeric conversions:
■ For %o, %x, or %X, print 0, 0x, or 0X prefix.
■ For %f, %e, or %E, print decimal point even when precision is 0.
■ For %g or %G, do not remove trailing zeros or decimal point.
Example: %#5.0f
■ Field width
Minimum number of characters to print. Can be a number, or an asterisk (*) to refer to an argument in the input list. For example, the input list
('%12d', intmax) is equivalent to ('%*d', 12, intmax).
■ Precision
For %f, %e, or %E:
Number of digits to the right of the decimal point.
Example: '%6.4f' prints pi as '3.1416'
For %g or %G
Number of significant digits.
Example: '%6.4g' prints pi as ' 3.142'
Can be a number, or an asterisk (*) to refer to an argument in the input list. For example, the input list ('%6.4f', pi) is equivalent to ('%
*.*f', 6, 4, pi).
The string can also include combinations of the following:
■ Literal text to print. To print a single quotation mark, include '' in formatSpec.
■ Control characters, including:
%%
Percent character
\\
Backslash
\a
Alarm
\b
Backspace
\f
Form feed
\n
New line
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Write data to text file - MATLAB fprintf
\r
Carriage return
\t
Horizontal tab
\v
Vertical tab
\xN
Character whose ASCII code is the hexadecimal number, N
\N
Character whose ASCII code is the octal number, N
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The following limitations apply to conversions:
■ Numeric conversions print only the real component of complex numbers.
■ If you specify a conversion that does not fit the data, such as a string conversion for a numeric value, MATLAB overrides the specified
conversion, and uses %e.
■ If you apply a string conversion (%s) to integer values, MATLAB converts values that correspond to valid character codes to characters. For
example, '%s' converts [65 66 67] to ABC.
A1,...,An — Numeric or character arrays
scalar | vector | matrix | multidimensional array
Numeric or character arrays, specified as a scalar, vector, matrix, or multidimensional array.
Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | char
Output Arguments
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nbytes — Number of bytes
scalar
Number of bytes that fprintf writes, returned as a scalar. When writing to a file, nbytes is determined by the character encoding. When printing
data to the screen, nbytes is the number of characters displayed on the screen.
More About
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Tips
■ Format specifiers for the reading functions sscanf and fscanf differ from the formats for the writing functions sprintf and fprintf. The
reading functions do not support a precision field. The width field specifies a minimum for writing but a maximum for reading.
■ Formatting Strings
References
[1] Kernighan, B. W., and D. M. Ritchie, The C Programming Language, Second Edition, Prentice-Hall, Inc., 1988.
[2] ANSI specification X3.159-1989: "Programming Language C," ANSI, 1430 Broadway, New York, NY 10018.
See Also
disp | fclose | ferror | fopen | fread | fscanf | fseek | ftell | fwrite | sprintf
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