cs534 - more printf stuff
Write the formatted arguments to the standard output under the control of the format
SYNTAX
printf format [arguments ...]
OPTIONS
| Symbol | Meaning/Usage |
|---|
| di | The argument is printed as a signed decimal (d or i), respectively |
|---|
| o | The argument is printed as an unsigned octal |
|---|
| u | The argument is printed as an unsigned decimal |
|---|
| oXx | The argument is printed as an unsigned hexadecimal |
|---|
| f | The argument is printed in the style [-]ddd.ddd where the
number of d's after the decimal point is equal to the preci-
sion specification for the argument. If the precision is
missing, 6 digits are given; if the precision is explicitly
0, no digits and no decimal point are printed. |
|---|
| eE | The argument is printed in the style [-]d.ddde+-dd where
there is one digit before the decimal point and the number
after is equal to the precision specification for the argu-
ment; when the precision is missing, 6 digits are produced.
An upper-case E is used for an `E' format. |
|---|
| gG | The argument is printed in style f or in style e (E)
whichever gives full precision in minimum space. |
|---|
| b | Characters from the string argument are printed with back- slash-escape sequences expanded. |
|---|
| c | The first character of argument is printed |
|---|
| s | Characters from the string argument are printed until the end
is reached or until the number of characters indicated by the
precision specification is reached; however if the precision
is 0 or missing, all characters in the string are printed |
|---|
| % | Print a `%'; no argument is used |
|---|
The format is a character string which contains three types of objects:
| character string | where it goes |
|---|
| plain characters | simply copied to standard output |
|---|
| character escape sequences | converted and copied to standard output |
|---|
| format specifications | causes printing of the next successive argument |
|---|
The arguments after the first are treated as strings if the corresponding
format is either b, c or s
Otherwise it is evaluated as a C constant, with the following extensions:
A leading plus or minus sign is allowed
If the leading character is a single or double quote, the value is the ASCII code of the next character
The format string is reused as often as necessary to satisfy the arguments
Any extra format specifications are evaluated with zero or the null string
Character escape sequences are in backslash notation as defined in ANSI X3.159-1989 (`ANSI C')
The characters and their meanings are as follows:
| escape sequence | what is does |
|---|
| \e | Write an <escape> character |
|---|
| \a | Write a <bell> character |
|---|
| \b | Write a <backspace> character |
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| \f | Write a <form-feed> character |
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| \n | Write a <new-line> character |
|---|
| \r | Write a <carriage return> character |
|---|
| \t | Write a <tab> character |
|---|
| \v | Write a <vertical tab> character |
|---|
| \' | Write a <single quote> character |
|---|
| \\ | Write a backslash character |
|---|
| \num | Write an 8-bit character whose ASCII value is the 1-, 2-, or 3-digit octal number num |
|---|
EXTREMELY IMPORTANT: Each format specification is introduced by the percent character (`%')
The remainder of the format specification includes zero or more of the following flags, in the following order:
| flag | what it does |
|---|
| # | Signifies that the value should be printed in an `alternative form' |
|---|
For c, d, and s,formats, this option has no effect
For the o formats the precision of the number is increased to force the first character of the output string to a zero
For the x (X) format, a non-zero result has the string 0x (0X) prepended to it
For e, E, f, g, and G, formats, the result will always contain a decimal point,
even if no digits follow the point (normally, a decimal point only appears in the results of those formats if a
digit follows the decimal point)
For g and G formats, trailing zeros are not removed from the result as they would otherwise be
Character escape sequences are converted and copied to standard output
Format specifications cause printing of the next successive argument
| - | A minus sign `-' which specifies left adjustment of the output in the indicated field |
|---|
| + | A `+' character specifying that there should always be a sign placed before the number when using signed formats |
|---|
| ` ' | A space specifying that a blank should be left before a positive number for a signed format. A `+' overrides a space if both are used |
|---|
.
| 0 | A zero `0' character indicating that zero-padding should be used rather than blank-padding. A `-' overrides a `0' if both are used |
|---|
;
Field Width
An optional digit string specifying a field width
if the output string has fewer characters than the field width it will be blank-padded on the left
(or right, if the left-adjustment indicator has been given) to make up the field width (note that a
leading zero is a flag, but an embedded zero is part of a field width);
Precision
An optional period, `.', followed by an optional digit string giving a precision which specifies
the number of digits to appear after the decimal point, for e and f formats, or the maximum
number of characters to be printed from a string
if the digit string is missing, the precision is treated as zero
Format
A character which indicates the type of format to use (one of d i o u x X f w E g G b c s)
A field width or precision may be `*' instead of a digit string
In this case an argument supplies the field width or precision
Examples
# Print a decimal number
$ printf "%d\n" 5
5
# Print as float (default 6 decimal places)
$ printf "%f\n" 5
5.000000
# Using \n to start a new line:
$ printf "Two separate\nlines\n"
Two separate
lines
# Print decimal numbers interspersed with text
$ printf "There are %d orders valued at over %d euros.\n" 64 1500
There are 64 orders valued at over 1500 euros.
# Convert a hex number to decimal
$ printf "%d\n " 0xF
15
# Convert a decimal number to Hex
$ printf "0x%X\n " 15
0xF
# Convert a decimal number to Octal
$ printf "0%o\n " 8
010
Notes
In no case does a non-existent or small field width cause truncation of a field
padding takes place only if the specified field width exceeds the actual width
Since the floating point numbers are translated from ASCII to floating- point and then back again,
floating-point precision may be lost
Parsing of arguments is also somewhat different between versions of printf( ),
where unknown arguments are simply printed instead of being flagged as errors
Exits 0 on success, and 1 on failure