14.2.4 Formatted Output

This section describes how to call printf and related functions.

The following functions are available for formatted output. They are modeled after the C language functions of the same name, but they interpret the format template differently in order to improve the performance of printing vector and matrix values.

Implementation Note: For compatibility with MATLAB, escape sequences in the template string (e.g., "\n" => newline) are expanded even when the template string is defined with single quotes.

: printf (template, …) ¶

: numbytes = printf (…) ¶

Print optional arguments under the control of the template string template to the stream stdout and return the number of characters printed.

See the Formatted Output section of the GNU Octave manual for a complete description of the syntax of the template string.

The optional output numbytes returns the number of bytes printed.

Implementation Note: For compatibility with MATLAB, escape sequences in the template string (e.g., "\n" => newline) are expanded even when the template string is defined with single quotes.

See also: fprintf, sprintf, scanf.

: fprintf (fid, template, …) ¶

: fprintf (template, …) ¶

: numbytes = fprintf (…) ¶

This function is equivalent to printf, except that the output is written to the file descriptor fid instead of stdout.

If fid is omitted, the output is written to stdout making the function exactly equivalent to printf.

The optional output numbytes returns the number of bytes written to the file.

Implementation Note: For compatibility with MATLAB, escape sequences in the template string (e.g., "\n" => newline) are expanded even when the template string is defined with single quotes.

See also: fputs, fdisp, fwrite, fscanf, printf, sprintf, fopen.

: str = sprintf (template, …) ¶

This is like printf, except that the output is returned as a string.

Unlike the C library function, which requires you to provide a suitably sized string as an argument, Octave’s sprintf function returns the string, automatically sized to hold all of the items converted.

Implementation Note: For compatibility with MATLAB, escape sequences in the template string (e.g., "\n" => newline) are expanded even when the template string is defined with single quotes.

See also: printf, fprintf, sscanf.

The printf function can be used to print any number of arguments. The template string argument you supply in a call provides information not only about the number of additional arguments, but also about their types and what style should be used for printing them.

Ordinary characters in the template string are simply written to the output stream as-is, while conversion specifications introduced by a ‘%’ character in the template cause subsequent arguments to be formatted and written to the output stream. For example,

pct = 37;
filename = "foo.txt";
printf ("Processed %d%% of '%s'.\nPlease be patient.\n",
        pct, filename);

produces output like

Processed 37% of 'foo.txt'.
Please be patient.

This example shows the use of the ‘%d’ conversion to specify that a scalar argument should be printed in decimal notation, the ‘%s’ conversion to specify printing of a string argument, and the ‘%%’ conversion to print a literal ‘%’ character.

There are also conversions for printing an integer argument as an unsigned value in octal, decimal, or hexadecimal radix (‘%o’, ‘%u’, or ‘%x’, respectively); or as a character value (‘%c’).

Floating-point numbers can be printed in normal, fixed-point notation using the ‘%f’ conversion or in exponential notation using the ‘%e’ conversion. The ‘%g’ conversion uses either ‘%e’ or ‘%f’ format, depending on what is more appropriate for the magnitude of the particular number.

You can control formatting more precisely by writing modifiers between the ‘%’ and the character that indicates which conversion to apply. These slightly alter the ordinary behavior of the conversion. For example, most conversion specifications permit you to specify a minimum field width and a flag indicating whether you want the result left- or right-justified within the field.

The specific flags and modifiers that are permitted and their interpretation vary depending on the particular conversion. They’re all described in more detail in the following sections.