bionic (3) strvis.3bsd.gz

NAME

     vis, strvis, strnvis, strvisx — visually encode characters

LIBRARY

     library “libbsd”

SYNOPSIS

     #include <stdlib.h>
     #include <vis.h>
     (See libbsd(7) for include usage.)

     char *
     vis(char *dst, int c, int flag, int nextc);

     int
     strvis(char *dst, const char *src, int flag);

     int
     strnvis(char *dst, const char *src, size_t size, int flag);

     int
     strvisx(char *dst, const char *src, size_t len, int flag);

DESCRIPTION

     The vis() function copies into dst a string which represents the character c.  If c needs no encoding, it
     is copied in unaltered.  The string is NUL terminated and a pointer to the end of the string is returned.
     The maximum length of any encoding is four characters (not including the trailing NUL); thus, when encoding
     a set of characters into a buffer, the size of the buffer should be four times the number of characters
     encoded, plus one for the trailing NUL.  The flag parameter is used for altering the default range of
     characters considered for encoding and for altering the visual representation.  The additional character,
     nextc, is only used when selecting the VIS_CSTYLE encoding format (explained below).

     The strvis(), strnvis() and strvisx() functions copy into dst a visual representation of the string src.
     The strvis() function encodes characters from src up to the first NUL.  The strnvis() function encodes
     characters from src up to the first NUL or the end of dst, as indicated by size.  The strvisx() function
     encodes exactly len characters from src (this is useful for encoding a block of data that may contain
     NULs).  All three forms NUL terminate dst, except for strnvis() when size is zero, in which case dst is not
     touched.  For strvis() and strvisx(), the size of dst must be four times the number of characters encoded
     from src (plus one for the NUL).  strvis() and strvisx() return the number of characters in dst (not
     including the trailing NUL).  strnvis() returns the length that dst would become if it were of unlimited
     size (similar to snprintf(3) or strlcpy(3bsd)).  This can be used to detect truncation but it also means
     that the return value of strnvis() must not be used without checking it against size.

     The encoding is a unique, invertible representation composed entirely of graphic characters; it can be
     decoded back into the original form using the unvis(3bsd) or strunvis(3bsd) functions.

     There are two parameters that can be controlled: the range of characters that are encoded, and the type of
     representation used.  By default, all non-graphic characters except space, tab, and newline are encoded
     (see isgraph(3)).  The following flags alter this:

     VIS_GLOB    Also encode magic characters recognized by glob(3) (‘*’, ‘?’, ‘[’) and ‘#’.

     VIS_SP      Also encode space.

     VIS_TAB     Also encode tab.

     VIS_NL      Also encode newline.

     VIS_WHITE   Synonym for VIS_SP | VIS_TAB | VIS_NL.

     VIS_SAFE    Only encode “unsafe” characters.  These are control characters which may cause common terminals
                 to perform unexpected functions.  Currently this form allows space, tab, newline, backspace,
                 bell, and return -- in addition to all graphic characters -- unencoded.

     There are three forms of encoding.  All forms use the backslash ‘\’ character to introduce a special
     sequence; two backslashes are used to represent a real backslash.  These are the visual formats:

     (default)   Use an ‘M’ to represent meta characters (characters with the 8th bit set), and use a caret ‘^’
                 to represent control characters (see iscntrl(3)).  The following formats are used:

                 \^C    Represents the control character ‘C’.  Spans characters ‘\000’ through ‘\037’, and
                        ‘\177’ (as ‘\^?’).

                 \M-C   Represents character ‘C’ with the 8th bit set.  Spans characters ‘\241’ through ‘\376’.

                 \M^C   Represents control character ‘C’ with the 8th bit set.  Spans characters ‘\200’ through
                        ‘\237’, and ‘\377’ (as ‘\M^?’).

                 \040   Represents ASCII space.

                 \240   Represents Meta-space.

     VIS_CSTYLE  Use C-style backslash sequences to represent standard non-printable characters.  The following
                 sequences are used to represent the indicated characters:

                       \a - BEL (007)
                       \b - BS (010)
                       \f - NP (014)
                       \n - NL (012)
                       \r - CR (015)
                       \s - SP (040)
                       \t - HT (011)
                       \v - VT (013)
                       \0 - NUL (000)

                 When using this format, the nextc parameter is looked at to determine if a NUL character can be
                 encoded as ‘\0’ instead of ‘\000’.  If nextc is an octal digit, the latter representation is
                 used to avoid ambiguity.

     VIS_OCTAL   Use a three digit octal sequence.  The form is ‘\ddd’ where d represents an octal digit.

     There is one additional flag, VIS_NOSLASH, which inhibits the doubling of backslashes and the backslash
     before the default format (that is, control characters are represented by ‘^C’ and meta characters as
     ‘M-C’).  With this flag set, the encoding is ambiguous and non-invertible.

SEE ALSO

     unvis(1), vis(1), snprintf(3), strlcpy(3bsd), unvis(3bsd)

HISTORY

     The vis(), strvis() and strvisx() functions first appeared in 4.4BSD.  The strnvis() function first
     appeared in OpenBSD 2.9.