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# Printf (Formatted Output)

`printf`()
  Name:
    printf, fprint, sprint --- formatted output
  Syntax:

    `printf(format, ...)`

    `fprint(format, ...)`

    `sprint(string, format, ...)`

  Description:

    `Printf` places output on the standard output. `fprint` places output on the file opened with the `wopen(filename)` command (standard output if no file is opened). `Sprint` places output in its string argument. These functions are subsets of their counterparts in the C standard library.

    Each of these functions converts, formats, and prints its arguments after the format string under control of the format string.

    The format string contains two types of objects: plain characters which are simply printed, and conversion specifications each of which causes conversion and printing of the next successive argument.

    Each conversion specification is introduced by the character '`%`' and ends with a conversion type specifier. The type specifiers supported are:

    f
      signed value of the form -dddd.ddddd
    e
      signed value of the form -d.dddddde-nn
    g
      signed value in either 'e' or 'f' form based on given value and precision. Trailing zeros and the decimal point are printed only if necessary.
    d
      signed value truncated and printed as integer.
    o
      printed as unsigned octal integer.
    x
      printed as unsigned hexadecimal integer
    c
      number treated as ascii code and printed as single character
    s
      string is printed, arg must be a string.

    Between `%` and the conversion type, optional flags, width, precision and size specifiers can be placed. The most useful flag is '-' which left justifies the result, otherwise the number is right justified in its field. Width and precision specifiers are of the form `width.precis`.

    Special characters of note are:

    `\n`
      newline
    `\t`
      tab
    `\r`
      carriage return without the line feed

    `printf` and `fprint` return the number of characters printed.

  Example:

  >     printf("\tpi=%-20.10g sin(pi)=%f\n", PI, sin(PI))
  >             pi=3.141592654          sin(pi)=0.000000
  >             42

  See also

  `File.ropen()`

  Warning

  Only a subset of the C standard library functions.

# Redirect Standard Out

`hoc_stdio`()
  Syntax:

    `hoc_stdout("filename")`

    `hoc_stdout()`

  Description:

    With a filename argument, switches the original standard out to filename. With no arguments. switches current standard out back to original filename.

    Only one level of switching allowed. Switching back to original causes future output to append to the stdout. Switching to "filename" writes stdout from the beginning of the file.

  Example:

  >     proc p() {
  >         print "one" // to original standard out
  >             hoc_stdout("temp.tmp")
  >             print "two" // to temp.tmp
  >         forall psection() // to temp.tmp
  >             hoc_stdout()
  >             print "three" // to original standard out
  >     }
  >     p()

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