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Printf with backreference in ruby
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PRINTF(3S) PRINTF(3S) NAME
printf, fprintf, sprintf, vfprintf, vsprintf - formatted output conversion SYNOPSIS
#include <stdio.h> char *printf(format [, arg ] ... ) char *format; char *fprintf(stream, format [, arg ] ... ) FILE *stream; char *format; int sprintf(s, format [, arg ] ... ) char *s, *format; #include <varargs.h> char *vprintf(format, args) char *format; va_list args; char *vfprintf(stream, format, args) FILE *stream; char *format; va_list args; int vsprintf(s, format, args) char *s, *format; va_list args; DESCRIPTION
Printf places output on the standard output stream stdout. Fprintf places output on the named output stream. Sprintf places `output' in the string s, followed by the character ` '. Alternate forms, in which the arguments have already been captured using the variable-length argument facilities of varargs(3), are available under the names vprintf, vfprintf, and vsprintf. Each of these functions converts, formats, and prints its arguments after the first under control of the first argument. The first argu- ment is a character string which contains two types of objects: plain characters, which are simply copied to the output stream, and conver- sion specifications, each of which causes conversion and printing of the next successive arg printf. Each conversion specification is introduced by the character %. The remainder of the conversion specification includes in the following order o a minus sign `-' which specifies left adjustment of the converted value in the indicated field; o an optional digit string specifying a field width; if the converted value 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; if the field width begins with a zero, zero-padding will be done instead of blank-padding; o 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-conversion, or the maximum number of characters to be printed from a string; o the character l specifying that a following d, o, x, or u corresponds to a long integer arg; o a character which indicates the type of conversion to be applied. A field width or precision may be `*' instead of a digit string. In this case an integer arg supplies the field width or precision. The conversion characters and their meanings are dox The integer arg is converted to signed decimal, unsigned octal, or unsigned hexadecimal notation respectively. f The float or double arg is converted to decimal notation in the style `[-]ddd.ddd' where the number of d's after the decimal point is equal to the precision 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. e The float or double arg is converted 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 argument; when the precision is missing, 6 digits are produced. g The float or double arg is printed in style d, in style f, or in style e, whichever gives full precision in minimum space. c The character arg is printed. s Arg is taken to be a string (character pointer) and characters from the string are printed until a null character or until the num- ber of characters indicated by the precision specification is reached; however if the precision is 0 or missing all characters up to a null are printed. u The unsigned integer arg is converted to decimal and printed (the result will be in the range 0 through MAXUINT, where MAXUINT equals 4294967295 on a VAX-11 and 65535 on a PDP-11). % Print a `%'; no argument is converted. 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. Characters generated by printf are printed as by putc(3S). RETURN VALUE
The functions all return the number of characters printed, or -1 if an error occurred. EXAMPLES
To print a date and time in the form `Sunday, July 3, 10:02', where weekday and month are pointers to null-terminated strings: printf("%s, %s %d, %02d:%02d", weekday, month, day, hour, min); To print pi to 5 decimals: printf("pi = %.5f", 4*atan(1.0)); SEE ALSO
putc(3S), scanf(3S) BUGS
Very wide fields (>300 characters) fail. Only sprintf and vsprintf return a count of characters transferred. The functions still supports %D, %O, %U and %X. Do not use these formats, as they will be disappearing real soon now. 7th Edition August 10, 1988 PRINTF(3S)
